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Encyclopaedia Britannica, 11th Edition, "Diameter" to "Dinarchus"

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Title: Encyclopaedia Britannica, 11th Edition, "Diameter" to "Dinarchus"

Author: Various


        
Release date: May 30, 2010 [eBook #32607]
                Most recently updated: January 6, 2021

Language: English

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Distributed Proofreading Team at https://www.pgdp.net









Transcriber's notes:

(1) Numbers following letters (without space) like C2 were originally
      printed in subscript. Letter subscripts are preceded by an
      underscore, like C_n.

(2) Characters following a carat (^) were printed in superscript.

(3) Side-notes were relocated to function as titles of their respective
      paragraphs.

(4) Letters topped by Macron are represented as [=x].

(5) dP stands for the partial-derivative symbol, or curled 'd'.

(6) [oo] stands for the infinity symbol, and [int] for the integral
       symbol.

(7) The following typographical errors have been corrected:

    Article DIAMOND: "If this be so the form of the diamond is really
      the tetrahedron (and the various figures derived symmetrically from
      it) and not the octahedron". 'octahedron' amended from
      'octadehron'.

    Article DIARY: "diaries began to be largely written in England,
      although in most cases without any idea of even eventual
      publication". 'largely' amended from 'largly'.

    Article DICOTYLEDONS: "The arrangement of the conducting tissue in
      the stem is characteristic; a transverse section of the very young
      stem shows a number of distinct conducting strands". 'number'
      amended from 'nunber'.

    Article DIEKIRCH: "It remained more or less fortified until the
      beginning of the 19th century when the French during their
      occupation levelled the old walls, and substituted the avenues of
      trees that now encircle the town". 'or' amended from 'for'.

    Article DIFFERENCES, CALCULUS OF: "as the second difference of u_n,
      and therefore as corresponding to the value x_n"; 'difference'
      amended from 'dfference'.

    Article DINAJPUR: "a town (with a population in 1901 of 13,430) and
     district of British India, in the Rajshahi division of Eastern
     Bengal and Assam". 'British' amended from 'Britsh'.




          ENCYCLOPAEDIA BRITANNICA

  A DICTIONARY OF ARTS, SCIENCES, LITERATURE
           AND GENERAL INFORMATION

              ELEVENTH EDITION


           VOLUME VIII, SLICE IV

           Diameter to Dinarchus




ARTICLES IN THIS SLICE:


  DIAMETER                             DIEDENHOFEN
  DIAMOND                              DIEKIRCH
  DIAMOND NECKLACE, THE AFFAIR OF THE  DIELECTRIC
  DIANA                                DIELMANN, FREDERICK
  DIANA MONKEY                         DIEMEN, ANTHONY VAN
  DIANE DE FRANCE                      DIEPENBECK, ABRAHAM VAN
  DIANE DE POITIERS                    DIEPPE
  DIAPASON                             DIERX, LÉON
  DIAPER                               DIES, CHRISTOPH ALBERT
  DIAPHORETICS                         DIEST
  DIAPHRAGM                            DIESTERWEG, FRIEDRICH ADOLF WILHELM
  DIARBEKR                             DIET
  DIARRHOEA                            DIETARY
  DIARY                                DIETETICS
  DIASPORE                             DIETRICH, CHRISTIAN WILHELM ERNST
  DIASTYLE                             DIETRICH OF BERN
  DIATOMACEAE                          DIEZ, FRIEDRICH CHRISTIAN
  DIAULOS                              DIEZ
  DIAVOLO, FRA                         DIFFERENCES, CALCULUS OF
  DIAZ, NARCISSE VIRGILIO              DIFFERENTIAL EQUATION
  DIAZ, PORFIRIO                       DIFFLUGIA
  DIAZ DE NOVAES, BARTHOLOMEU          DIFFRACTION OF LIGHT
  DIAZO COMPOUNDS                      DIFFUSION
  DIAZOMATA                            DIGBY, SIR EVERARD
  DIBDIN, CHARLES                      DIGBY, SIR KENELM
  DIBDIN, THOMAS FROGNALL              DIGBY, KENELM HENRY
  DIBDIN, THOMAS JOHN                  DIGENES ACRITAS, BASILIUS
  DIBRA                                DIGEST
  DIBRUGARH                            DIGESTIVE ORGANS
  DICAEARCHUS                          DIGGES, WEST
  DICE                                 DIGIT
  DICETO, RALPH DE                     DIGITALIS
  DICEY, EDWARD                        DIGNE
  DICHOTOMY                            DIGOIN
  DICK, ROBERT                         DIJON
  DICK, THOMAS                         DIKE
  DICKENS, CHARLES JOHN HUFFAM         DIKKA
  DICKINSON, ANNA ELIZABETH            DILAPIDATION
  DICKINSON, JOHN                      DILATATION
  DICKSON, SIR ALEXANDER               DILATORY
  DICKSON, SIR JAMES ROBERT            DILEMMA
  DICOTYLEDONS                         DILETTANTE
  DICTATOR                             DILIGENCE
  DICTIONARY                           DILKE, SIR CHARLES WENTWORTH
  DICTYOGENS                           DILL
  DICTYS CRETENSIS                     DILLEN, JOHANN JAKOB
  DICUIL                               DILLENBURG
  DIDACHE, THE                         DILLENS, JULIEN
  DIDACTIC POETRY                      DILLINGEN
  DIDEROT, DENIS                       DILLMANN, CHRISTIAN AUGUST
  DIDIUS SALVIUS JULIANUS, MARCUS      DILLON, ARTHUR RICHARD
  DIDO                                 DILLON, JOHN
  DIDON, HENRI                         DILUVIUM
  DIDOT                                DIME
  DIDRON, ADOLPHE NAPOLÉON             DIMENSION
  DIDYMI                               DIMITY
  DIDYMIUM                             DINAJPUR
  DIDYMUS                              DINAN
  DIDYMUS CHALCENTERUS                 DINANT
  DIE (town of France)                 DINAPUR
  DIE (datum)                          DINARCHUS
  DIEBITSCH, HANS KARL FRIEDRICH ANTON




DIAMETER (from the Gr. [Greek: dia], through, [Greek: metron],
measure), in geometry, a line passing through the centre of a circle or
conic section and terminated by the curve; the "principal diameters" of
the ellipse and hyperbola coincide with the "axes" and are at right
angles; "conjugate diameters" are such that each bisects chords parallel
to the other. The diameter of a quadric surface is a line at the
extremities of which the tangent planes are parallel. Newton defined the
diameter of a curve of any order as the locus of the centres of the mean
distances of the points of intersection of a system of parallel chords
with the curve; this locus may be shown to be a straight line. The word
is also used as a unit of linear measurement of the magnifying power of
a lens or microscope.

In architecture, the term is used to express the measure of the lower
part of the shaft of a column. It is employed by Vitruvius (iii. 2) to
determine the height of a column, which should vary from eight to ten
diameters according to the intercolumniation: and it is generally the
custom to fix the lower diameter of the shaft by the height required and
the Order employed. Thus the diameter of the Roman Doric should be about
one-eighth of the height, that of the Ionic one-ninth, and of the
Corinthian one-tenth (see ORDER).




DIAMOND, a mineral universally recognized as chief among precious
stones; it is the hardest, the most imperishable, and also the most
brilliant of minerals.[1] These qualities alone have made it supreme as
a jewel since early times, and yet the real brilliancy of the stone is
not displayed until it has been faceted by the art of the lapidary
(q.v.); and this was scarcely developed before the year 1746. The
consummate hardness of the diamond, in spite of its high price, has made
it most useful for purposes of grinding, polishing and drilling.
Numerous attempts have been made to manufacture the diamond by
artificial means, and these attempts have a high scientific interest on
account of the mystery which surrounds the natural origin of this
remarkable mineral. Its physical and chemical properties have been the
subject of much study, and have a special interest in view of the
extraordinary difference between the physical characters of the diamond
and those of graphite (blacklead) or charcoal, with which it is
chemically identical, and into which it can be converted by the action
of heat or electricity. Again, on account of the great value of the
diamond, much of the romance of precious stones has centred round this
mineral; and the history of some of the great diamonds of historic times
has been traced through many extraordinary vicissitudes.

The name [Greek: Adamas], "the invincible," was probably applied by the
Greeks to hard metals, and thence to corundum (emery) and other hard
stones. According to Charles William King, the first undoubted
application of the name to the diamond is found in Manilius (A.D.
16),--_Sic Adamas_, _punctum lapidis_, _pretiosior auro_,--and Pliny
(A.D. 100) speaks of the rarity of the stone, "the most valuable of
gems, known only to kings." Pliny described six varieties, among which
the Indian, having six pointed angles, and also resembling two pyramids
(_turbines_, whip-tops) placed base to base, may probably be identified
as the ordinary octahedral crystal (fig. 1). The "diamond" (_Yahalom_)
in the breastplate of the high priest (Ex. xxxix. 11) was certainly some
other stone, for it bore the name of a tribe, and methods of engraving
the true diamond cannot have been known so early. The stone can hardly
have become familiar to the Romans until introduced from India, where it
was probably mined at a very early period. But one or other of the
remaining varieties mentioned by Pliny (the Macedonian, the Arabian, the
Cyprian, &c.) may be the true diamond, which was in great request for
the tool of the gem-engraver. Later Roman authors mentioned various
rivers in India as yielding the _Adamas_ among their sands. The name
_Adamas_ became corrupted into the forms _adamant_, _diamaunt_,
_diamant_, _diamond_; but the same word, owing to a medieval
misinterpretation which derived it from _adamare_ (compare the French
word _aimant_), was also applied to the lodestone.

Like all the precious stones, the diamond was credited with many
marvellous virtues; among others the power of averting insanity, and of
rendering poison harmless; and in the middle ages it was known as the
"pietra della reconciliazione," as the peacemaker between husband and
wife.

_Scientific Characters._--The majority of minerals are found most
commonly in masses which can with difficulty be recognized as aggregates
of crystalline grains, and occur comparatively seldom as distinct
crystals; but the diamond is almost always found in single crystals,
which show no signs of previous attachment to any matrix; the stones
were, until the discovery of the South African mines, almost entirely
derived from sands or gravels, but owing to the hardness of the mineral
it is rarely, if ever, water-worn, and the crystals are often very
perfect. The crystals belong to the cubic system, generally assuming the
form of the octahedron (fig. 1), but they may, in accordance with the
principles of crystallography, also occur in other forms symmetrically
derived from the octahedron,--for example, the cube, the 12-faced figure
known as the rhombic dodecahedron (fig. 2), or the 48-faced figure known
as the hexakis-octahedron (fig. 3), or in combinations of these. The
octahedron faces are usually smooth; most of the other faces are rounded
(fig. 4). The cube faces are rough with protruding points. The cube is
sometimes found in Brazil, but is very rare among the S. African stones;
and the dodecahedron is perhaps more common in Brazil than elsewhere.
There is often a furrow running along the edges of the octahedron, or
across the edges of the cube, and this indicates that the apparently
simple crystal may really consist of eight individuals meeting at the
centre; or, what comes to the same thing, of two individuals
interpenetrating and projecting through each other. If this be so the
form of the diamond is really the tetrahedron (and the various figures
derived symmetrically from it) and not the octahedron. Fig. 5 shows how
the octahedron with furrowed edge may be constructed from two
interpenetrating tetrahedra (shown in dotted lines). If the grooves be
left out of account, the large faces which have replaced each
tetrahedron corner then make up a figure which has the aspect of a
simple octahedron. Such regular interpenetrations are known in
crystallography as "twins." There are also twins of diamond in which two
octahedra (fig. 6) are united by contact along a surface parallel to an
octahedron face without interpenetration. On account of their
resemblance to the twins of the mineral spinel (which crystallizes in
octahedra) these are known as "spinel twins." They are generally
flattened along the plane of union. The crystals often display
triangular markings, either elevations or pits, upon the octahedron
faces; the latter are particularly well defined and have the form of
equilateral triangles (fig. 7). They are similar to the "etched figures"
produced by moistening an octahedron of alum, and have probably been
produced, like them, by the action of some solvent. Similar, but
somewhat different markings are produced by the combustion of diamond in
oxygen, unaccompanied by any rounding of the edges.

[Illustration: FIG. 1.]

[Illustration: FIG. 2.]

[Illustration: FIG. 3.]

[Illustration: FIG. 4.]

[Illustration: FIG. 5.]

[Illustration: FIG. 6.]

[Illustration: FIG. 7.]

Diamond possesses a brilliant "adamantine" lustre, but this tends to be
greasy on the surface of the natural stones and gives the rounded
crystals somewhat the appearance of drops of gum. Absolutely colourless
stones are not so common as cloudy and faintly coloured specimens; the
usual tints are grey, brown, yellow or white; and as rarities, red,
green, blue and black stones have been found. The colour can sometimes
be removed or changed at a high temperature, but generally returns on
cooling. It is therefore more probably due to metallic oxides than to
hydrocarbons. Sir William Crookes has, however, changed a pale yellow
diamond to a bluish-green colour by keeping it embedded in radium
bromide for eleven weeks. The black coloration upon the surface produced
by this process, as also by the electric bombardment in a vacuum tube,
appears to be due to a conversion of the surface film into graphite.
Diamond may break with a conchoidal fracture, but the crystals always
cleave readily along planes parallel to the octahedron faces: of this
property the diamond cutters avail themselves when reducing the stone to
the most convenient form for cutting; a sawing process, has, however,
now been introduced, which is preferable to that of cleavage. It is the
hardest known substance (though tantalum, or an alloy of tantalum now
competes with it) and is chosen as 10 in the mineralogist's scale of
hardness; but the difference in hardness between diamond (10) and
corundum (9) is really greater than that between corundum (9) and talc
(1); there is a difference in the hardness of the different faces; the
Borneo stones are also said to be harder than those of Australia, and
the Australian harder than the African, but this is by no means certain.
The specific gravity ranges from 3.56 to 3.50, generally about 3.52. The
coefficient of expansion increases very rapidly above 750°, and
diminishes very rapidly at low temperatures; the maximum density is
attained about -42° C.

The very high refractive power (index = 2.417 for sodium light) gives
the stone its extraordinary brilliancy; for light incident within a
diamond at a greater angle than 24½° is reflected back into the stone
instead of passing through it; the corresponding angle for glass is
40½°. The very high dispersion (index for red light = 2.402, for blue
light = 2.460) gives it the wonderful "fire" or display of spectral
colours. Certain absorption bands at the blue end of the spectrum are
supposed to be due to rare elements such as samarium. Unlike other cubic
crystals, diamond experiences a diminution of refractive index with
increase of temperature. It is very transparent for Röntgen rays,
whereas paste imitations are opaque. It is a good conductor of heat, and
therefore feels colder to the touch than glass and imitation stones. The
diamond has also a somewhat greasy feel. The specific heat increases
rapidly with rising temperature up to 60° C., and then more slowly.
Crystals belonging to the cubic system should not be birefringent unless
strained; diamond often displays double refraction particularly in the
neighbourhood of inclusions, both liquid and solid; this is probably due
to strain, and the spontaneous explosion of diamonds has often been
observed. Diamond differs from graphite in being a bad conductor of
electricity: it becomes positively electrified by friction. The
electrical resistance is about that of ordinary glass, and is diminished
by one-half during exposure by Röntgen rays; the dielectric constant
(16) is greater than that which should correspond to the specific
gravity.

The phosphorescence produced by friction has been known since the time
of Robert Boyle (1663); the diamond becomes luminous in a dark room
after exposure to sunlight or in the presence of radium; and many stones
phosphoresce beautifully (generally with a pale green light) when
subjected to the electric discharge in a vacuum tube. Some diamonds are
more phosphorescent than others, and different faces of a crystal may
display different tints. The combustibility of the diamond was predicted
by Sir Isaac Newton on account of its high refractive power; it was
first established experimentally by the Florentine Academicians in 1694.
In oxygen or air diamond burns at about 850°, and only continues to do
so if maintained at a high temperature; but in the absence of oxidising
agents it may be raised to a much higher temperature. It is, however,
infusible at the temperature of the electric arc, but becomes converted
superficially into graphite. Experiments on the combustion of diamond
were made by Smithson Tennant (1797) and Sir Humphry Davy (1816), with
the object of proving that it is pure carbon; they showed that burnt in
oxygen it yields exactly the same amount of carbon dioxide as that
produced by burning the same weight of carbon. Still more convincing
experiments were made by A. Krause in 1890. Similarly Guyton de Morveau
showed that, like charcoal, diamond converts soft iron into steel.
Diamond is insoluble in acid and alkalis, but is oxidised on heating
with potassium bichromate and sulphuric acid.

Bort (or Boart) is the name given to impure crystals or fragments
useless for jewels; it is also applied to the rounded crystalline
aggregates, which generally have a grey colour, a rough surface, often a
radial structure, and are devoid of good cleavage. They are sometimes
spherical ("shot bort"). Carbonado or "black diamond," found in Bahia
(also recently in Minas Geraes), is a black material with a minutely
crystalline structure somewhat porous, opaque, resembling charcoal in
appearance, devoid of cleavage, rather harder than diamond, but of less
specific gravity; it sometimes displays a rude cubic crystalline form.
The largest specimen found (1895) weighed 3078 carats. Both bort and
carbonado seem to be really aggregates of crystallized diamond, but the
carbonado is so nearly structureless that it was till recently regarded
as an amorphous modification of carbon.

_Uses of the Diamond._--The use of the diamond for other purposes than
jewelry depends upon its extreme hardness: it has always been the only
material used for cutting or engraving the diamond itself. The
employment of powdered bort and the lapidary's wheel for faceting
diamonds was introduced by L. von Berquen of Bruges in 1476. Diamonds
are now employed not only for faceting precious stones, but also for
cutting and drilling glass, porcelain, &c,; for fine engraving such as
scales; in dentistry for drilling; as a turning tool for electric-light
carbons, hard rubber, &c.; and occasionally for finishing accurate
turning work such as the axle of a transit instrument. For these tools
the stone is actually shaped to the best form: it is now electroplated
before being set in its metal mount in order to secure a firm fastening.
It is also used for bearings in watches and electric meters. The best
glaziers' diamonds are chosen from crystals such that a natural curved
edge can be used. For rock drills, and revolving saws for stone cutting,
either diamond, bort or carbonado is employed, set in steel tubes, disks
or bands. Rock drilling is the most important industrial application;
and for this, owing to its freedom from cleavage, the carbonado is more
highly prized than diamond; it is broken into fragments about 3 carats
in weight; and in 1905 the value of carbonado was no less than from £10
to £14 a carat. It has been found that the "carbons" in drills can
safely be subjected to a pressure of over 60 kilograms per square
millimetre, and a speed of 25 metres per second. A recent application of
the diamond is for wire drawing; a hole tapering towards the centre is
drilled through a diamond, and the metal is drawn through this. No other
tool is so endurable, or gives such uniform thickness of wire.

_Distribution and Mining._--The most important localities for diamonds
have been: (1) India, where they were mined from the earliest times till
the close of the 19th century; (2) South America, where they have been
mined since the middle of the 18th century; and (3) South Africa, to
which almost the whole of the diamond-mining industry has been
transferred since 1870.

  _India._--The diamond is here found in ancient sandstones and
  conglomerates, and in the river gravels and sands derived from them.
  The sandstones and conglomerates belong to the Vindhyan formation and
  overlie the old crystalline rocks: the diamantiferous beds are well
  defined, often not more than 1 ft. in thickness, and contain pebbles
  of quartzite, jasper, sandstone, slate, &c. The mines fall into five
  groups situated on the eastern side of the Deccan plateau about the
  following places (beginning from the south), the first three being in
  Madras. (1) Chennur near Cuddapah on the river Pennar. (2) Kurnool
  near Baneganapalle between the rivers Pennar and Kistna. (3) Kollar
  near Bezwada on the river Kistna. (4) Sambalpur on the river Mahanadi
  in the Central Provinces. (5) Panna near Allahabad, in Bundelkhand.
  The mining has always been carried on by natives of low caste, and by
  primitive methods which do not differ much from those described by the
  French merchant Jean Baptiste Tavernier (1605-1689), who paid a
  prolonged visit to most of the mines between 1638 and 1665 as a
  dealer in precious stones. According to his description shallow pits
  were sunk, and the gravel excavated was gathered into a walled
  enclosure where it was crushed and water was poured over it, and it
  was finally sifted in baskets and sorted by hand. The buying and
  selling was at that period conducted by young children. In more modern
  times there has been the same excavation of shallow pits, and
  sluicing, sifting and sorting, by hand labour, the only machinery used
  being chain pumps made of earthen bowls to remove the water from the
  deeper pits.

  At some of the Indian localities spasmodic mining has been carried on
  at different periods for centuries, at some the work which had been
  long abandoned was revived in recent times, at others it has long been
  abandoned altogether. Many of the large stones of antiquity were
  probably found in the Kollar group, where Tavernier found 60,000
  workers in 1645 (?), the mines having, according to native accounts,
  been discovered about 100 years previously. Golconda was the fortress
  and the market for the diamond industry at this group of mines, and so
  gave its name to them. The old mines have now been completely
  abandoned, but in 1891 about 1000 carats were being raised annually in
  the neighbourhood of Hyderabad. The Sambalpur group appear to have
  been the most ancient mines of all, but they were not worked later
  than 1850. The Panna group were the most productive during the 19th
  century. India was no doubt the source of all the large stones of
  antiquity; a stone of 67-3/8 carats was found at Wajra Karur in the
  Chennur group in 1881, and one of 210½ carats at Hira Khund in 1809.
  Other Indian localities besides those mentioned above are Simla, in
  the N.W. Provinces, where a few stones have been found, and a district
  on the Gouel and the Sunk rivers in Bengal, which V. Ball has
  identified with the Soumelpour mentioned by Tavernier. The mines of
  Golconda and Kurnool were described as early as 1677 in the twelfth
  volume of the _Philosophical Transactions_ of the Royal Society. At
  the present time very few Indian diamonds find their way out of the
  country, and, so far as the world's supply is concerned, Indian mining
  of diamonds may be considered extinct. The first blow to this industry
  was the discovery of the Brazilian mines in Minas Geraes and Bahia.

  _Brazil._---Diamonds were found about 1725 at Tejuco (now Diamantina)
  in Minas Geraes, and the mining became important about 1740. The chief
  districts in Minas Geraes are (1) Bagagem on the W. side of the Serra
  da Mata da Corda; (2) Rio Abaete on the E. side of the same range;
  these two districts being among the head waters of the Rio de San
  Francisco and its tributaries; (3) Diamantina, on and about the
  watershed separating the Rio de San Francisco from the Rio
  Jequitinhonha; and (4) Grao Mogul, nearly 200 m. to the N.E. of
  Diamantina on the latter river.

  The Rio Abaete district was worked on a considerable scale between
  1785 and 1807, but is now abandoned. Diamantina is at present the most
  important district; it occupies a mountainous plateau, and the
  diamonds are found both on the plateau and in the river valleys below
  it. The mountains consist here of an ancient laminated micaceous
  quartzite, which is in parts a flexible sandstone known as
  itacolumite, and in parts a conglomerate; it is interbedded with
  clay-slate, mica-schist, hornblende-schist and haematite-schist, and
  intersected by veins of quartz. This series is overlain unconformably
  by a younger quartzite of similar character, and itself rests upon the
  crystalline schists. The diamond is found under three conditions: (1)
  in the gravels of the present rivers, embedded in a ferruginous
  clay-cemented conglomerate known as _cascalho_; (2) in terraces
  (gupiarras) in a similar conglomerate occupying higher levels in the
  present valleys; (3) in plateau deposits in a coarse surface
  conglomerate known as _gurgulho_, the diamond and other heavy minerals
  being embedded in the red clay which cements the larger blocks. Under
  all these three conditions the diamond is associated with fragments of
  the rocks of the country and the minerals derived from them,
  especially quartz, hornstone, jasper, the polymorphous oxide of
  titanium (rutile, anatase and brookite), oxides and hydrates of iron
  (magnetite, ilmenite, haematite, limonite), oxide of tin, iron
  pyrites, tourmaline, garnet, xenotime, monazite, kyanite, diaspore,
  sphene, topaz, and several phosphates, and also gold. Since the heavy
  minerals of the _cascalho_ in the river beds are more worn than those
  of the terraces, it is highly probable that they have been derived by
  the cutting down of the older river gravels represented by the
  terraces; and since in both deposits the heavy minerals are more
  abundant near the heads of the valleys in the plateau, it is also
  highly probable that both have really been derived from the plateau
  deposit. In the latter, especially at São João da Chapada, the
  minerals accompanying the diamond are scarcely worn at all; in the
  terraces and the river beds they are more worn and more abundant; the
  terraces, therefore, are to be regarded as a first concentration of
  the plateau material by the old rivers; and the _cascalho_ as a second
  concentration by the modern rivers. The mining is carried on by
  negroes under the supervision of overseers; the _cascalho_ is dug out
  in the dry season and removed to a higher level, and is afterwards
  washed out by hand in running water in shallow wooden basins
  (_bateas_). The terraces can be worked at all seasons, and the
  material is partly washed out by leading streams on to it. The washing
  of the plateau material is effected in reservoirs of rain water.

  It is difficult to obtain an estimate of the actual production of the
  Minas Geraes mines, for no official returns have been published, but
  in recent years it has certainly been rivalled by the yield in Bahia.
  The diamond here occurs in river gravels and sands associated with
  the same minerals as in Minas Geraes; since 1844 the richest mines
  have been worked in the Serra de Cincora, where the mountains are
  intersected by the river Paraguassu and its tributaries; it is said
  that there were as many as 20,000 miners working here in 1845, and it
  was estimated that 54,000 carats were produced in Bahia in 1858. The
  earlier workings were in the Serra de Chapada to the N.W. of the mines
  just mentioned. In 1901 there were about 5000 negroes employed in the
  Bahia mines; methods were still primitive; the _cascalho_ was dug out
  from the river beds or tunnelled out from the valley side, and washed
  once a week in sluices of running water, where it was turned over with
  the hoe, and finally washed in wooden basins and picked over by hand;
  sometimes also the diamantiferous material is scooped out of the bed
  of the shallow rivers by divers, and by men working under water in
  caissons. It is almost exclusively in the mines of Bahia, and in
  particular in the Cincora district, that the valuable carbonado is
  found. The carbonado and the diamond have been traced to an extensive
  hard conglomerate which occurs in the middle of the sandstone
  formation. Diamonds are also mined at Salobro on the river Pardo not
  far inland from the port of Canavieras in the S.E. corner of Bahia.
  The enormous development of the South African mines, which supplied in
  1906, about 90% of the world's produce, has thrown into the shade the
  Brazilian production; but the _Bulletin_ for Feb. 1909 of the
  International Bureau of American Republics gave a very confident
  account of its future, under improved methods.

  _South Africa._---The first discovery was made in 1867 by Dr W. G.
  Atherstone, who identified as diamond a pebble obtained from a child
  in a farm on the banks of the Orange river and brought by a trader to
  Grahamstown; it was bought for £500 and displayed in the Paris
  Exhibition of that year. In 1869 a stone weighing 83½ carats was found
  near the Orange river; this was purchased by the earl of Dudley for
  £25,000 and became famous as the "Star of South Africa." A rush of
  prospectors at once took place to the banks of the Orange and Vaal
  rivers, and resulted in considerable discoveries, so that in 1870
  there was a mining camp of no less than 10,000 persons on the "River
  Diggings." In the River Diggings the mining was carried on in the
  coarse river gravels, and by the methods of the Brazilian negroes and
  of gold placer-miners. A diggers' committee limited the size of claims
  to 30 ft. square, with free access to the river bank; the gravel and
  sand were washed in cradles provided with screens of perforated metal,
  and the concentrates were sorted by hand on tables by means of an iron
  scraper.

  But towards the close of 1870 stones were found at Jagersfontein and
  at Dutoitspan, far from the Vaal river, and led to a second great rush
  of prospectors, especially to Dutoitspan, and in 1871 to what is now
  the Kimberley mine in the neighbourhood of the latter. At each of
  these spots the diamantiferous area was a roughly circular patch of
  considerable size, and in some occupied the position of one of those
  depressions or "pans" so frequent in S. Africa. These "dry diggings"
  were therefore at first supposed to be alluvial in origin like the
  river gravels; but it was soon discovered that, below the red surface
  soil and the underlying calcareous deposit, diamonds were also found
  in a layer of yellowish clay about 50 ft. thick known as "yellow
  ground." Below this again was a hard bluish-green serpentinous rock
  which was at first supposed to be barren bed-rock; but this also
  contained the precious stone, and has become famous, under the name of
  "blue ground," as the matrix of the S. African diamonds. The yellow
  ground is merely decomposed blue ground. In the Kimberley district
  five of these round patches of blue ground were found within an area
  little more than 3 m. in diameter; that at Kimberley occupying 10
  acres, that at Dutoitspan 23 acres. There were soon 50,000 workers on
  this field, the canvas camp was replaced by a town of brick and iron
  surrounded by the wooden huts of the natives, and Kimberley became an
  important centre.

  It was soon found that each mine was in reality a huge vertical funnel
  or crater descending to an unknown depth, and filled with
  diamantiferous blue ground. At first each claim was an independent pit
  31 ft. square sunk into the blue ground; the diamantiferous rock was
  hoisted by bucket and windlass, and roadways were left across the pit
  to provide access to the claims. But the roadways soon fell in, and
  ultimately haulage from the claims could only be provided by means of
  a vast system of wire ropes extending from a triple staging of
  windlasses erected round the entire edge of the mine, which had by
  this time become a huge open pit; the ropes from the upper windlasses
  extended to the centre, and those from the lower tier to the sides of
  the pit; covering the whole mass like a gigantic cobweb. (See Plate
  II. fig. 12.) The buckets of blue ground were hauled up these ropes by
  means of horse whims, and in 1875 steam winding engines began to be
  employed. By this time also improved methods in the treatment of the
  blue ground were introduced. It was carried off in carts to open
  spaces, where an exposure of some weeks to the air was found to
  pulverize the hard rock far more efficiently than the old method of
  crushing with mallets. The placer-miner's cradle and rocking-trough
  were replaced by puddling troughs stirred by a revolving comb worked
  by horse power; reservoirs were constructed for the scanty
  water-supply, bucket elevators were introduced to carry away the
  tailings; and the natives were confined in compounds. For these
  improvements co-operation was necessary; the better claims, which in
  1872 had risen from £100 to more than £4000 in value, began to be
  consolidated, and a Mining Board was introduced.


  PLATE I.

  [Illustration: FIG. 9.--DE BEERS MINE, 1874.]

  [Illustration: FIG. 10.--KIMBERLEY MINE, 1874.]

  [Illustration: FIG. 11.--DE BEERS MINE, 1873. (From photographs by C.
  Evans.)]


  PLATE II.

  [Illustration: _Fig. 12._--KIMBERLEY MINE, 1874.]

  [Illustration: _Fig. 13._--KIMBERLEY MINE, 1902. (From Photographs by
  C. Evans.)]


  In a very few years, however, the open pit mining was rendered
  impossible by the mud rushes, by the falls of the masses of barren
  rock known as "reef," which were left standing in the mine, and by
  landslips from the sides, so that in 1883, when the pit had reached a
  depth of about 400 ft., mining in the Kimberley crater had become
  almost impossible. By 1889, in the whole group of mines, Kimberley,
  Dutoitspan, De Beers and Bultfontein, open pit working was practically
  abandoned. Meanwhile mining below the bottom of the pits by means of
  shafts and underground tunnels had been commenced; but the full
  development of modern methods dates from the year 1889 when Cecil
  Rhodes and Alfred Beit, who had already secured control of the De
  Beers mine, acquired also the control of the Kimberley mine, and
  shortly afterwards consolidated the entire group in the hands of the
  De Beers Company. (See KIMBERLEY.)

  The scene of native mining was now transferred from the open pit to
  underground tunnels; the vast network of wire ropes (Plate II. fig.
  12) with their ascending and descending buckets disappeared, and with
  it the cosmopolitan crowd of busy miners working like ants at the
  bottom of the pit. In place of all this, the visitor to Kimberley
  encounters at the edge of the town only a huge crater, silent and
  apparently deserted, with no visible sign of the great mining
  operations which are conducted nearly half a mile below the surface.
  The aspect of the Kimberley pit in 1906 is shown in fig. 13 of Plate
  II., which may be compared with the section of fig. 8.

  In fig. 13, Plate II., the sequence of the basalt, shale and melaphyre
  is clearly visible on the sides of the pit; and fig. 8 shows how the
  crater or "pipe" of blue ground has penetrated these rocks and also
  the underlying quartzite. The workings at De Beers had extended into
  the still more deeply seated granite in 1906. Figure 9, Plate I.,
  shows the top of the De Beers' crater with basalt overlying the shale.
  Figure 8 also explains the modern system of mining introduced by
  Gardner Williams. A vertical shaft is sunk in the vicinity of the
  mine, and from this horizontal tunnels are driven into the pipe at
  different levels separated by intervals of 40 ft. Through the blue
  ground itself on each level a series of parallel tunnels about 120 ft.
  apart are driven to the opposite side of the pipe, and at right angles
  to these, and 36 ft. apart, another series of tunnels. When the
  tunnels reach the side of the mine they are opened upwards and
  sideways so as to form a large chamber, and the overlying mass of blue
  ground and débris is allowed to settle down and fill up the gallery.
  On each level this process is carried somewhat farther back than on
  the level below (fig. 8); material is thus continually withdrawn from
  one side of the mine and extracted by means of the rock shaft on the
  opposite side, while the superincumbent débris is continually sinking,
  and is allowed to fall deeper on the side farthest from the shaft as
  the blue ground is withdrawn from beneath it. In 1905 the main shaft
  had been sunk to a depth of 2600 ft. at the Kimberley mine.

  For the extraction and treatment of the blue ground the De Beers
  Company in its great winding and washing plant employs labour-saving
  machinery on a gigantic scale. The ground is transferred in trucks to
  the shaft where it is automatically tipped into skips holding 96 cubic
  ft. (six truck loads); these are rapidly hoisted to the surface, where
  their contents are automatically dumped into side-tipping trucks, and
  these in turn are drawn away in a continual procession by an endless
  wire rope along the tram lines leading to the vast "distributing
  floors." These are open tracts upon which the blue ground is spread
  out and left exposed to sun and rain until it crumbles and
  disintegrates, the process being hastened by harrowing with steam
  ploughs; this may require a period of three or six months, or even a
  year. The stock of blue ground on the floors at one time in 1905 was
  nearly 4,500,000 loads. The disintegrated ground is then brought back
  in the trucks and fed through perforated cylinders into the washing
  pans; the hard blue which has resisted disintegration on the floors,
  and the lumps which are too big to pass the cylindrical sieves, are
  crushed before going to the pans. These are shallow cylindrical
  troughs containing muddy water in which the diamonds and other heavy
  minerals (concentrates) are swept to the rim by revolving toothed
  arms, while the lighter stuff escapes near the centre of the pan. The
  concentrates are then passed over sloping tables (pulsator) and shaken
  to and fro under a stream of water which effects a second
  concentration of the heaviest material.

  Until recently the final separation of the diamond from the
  concentrates was made by hand picking, but even this has now been
  replaced by machinery, owing to the remarkable discovery that a
  greased surface will hold a diamond while allowing the other heavy
  minerals to pass over it. The concentrates are washed down a sloping
  table of corrugated iron which is smeared with grease, and it is found
  that practically all the diamonds adhere to the table, and the other
  minerals are washed away. At the large and important Premier mine in
  the Transvaal the Elmore process, used in British Columbia and in
  Wales for the separation of metallic ores, has been also introduced.
  In the Elmore process oil is employed to float off the materials which
  adhere to it, while the other materials remain in the water, the oil
  being separated from the water by centrifugal action. The other
  minerals found in the concentrates are pebbles and fragments of
  pyrope, zircon, cyanite, chrome-diopside, enstatite, a green pyroxene,
  mica, ilmenite, magnetite, chromite, hornblende, olivine, barytes,
  calcite and pyrites.

  In all the S. African mines the diamonds are not only crystals of
  various weights from fractions of a carat to 150 carats, but also
  occur as microscopic crystals disseminated through the blue ground. In
  spite of this, however, the average yield in the profitable mines is
  only from 0.2 carat to 0.6 carat per load of 1600 lb., or on an average
  about 1½ grs. per ton. The annual output of diamonds from the De Beers
  mines was valued in 1906 at nearly £5,000,000; the value per carat
  ranging from about 35s. to 70s.

  [Illustration: SECTION OF KIMBERLEY MINE LOOKING EAST

  From Gardner Williams's _Diamond Mines of South Africa_. FIG. 8.]

  Pipes similar to those which surround Kimberley have been found in
  other parts of S. Africa. One of the best known is that of
  Jagersfontein, which was really the first of the dry diggings
  (discovered in 1870). This large mine is near Fauresmith and 80 m. to
  the south of Kimberley. In 1905 the year's production from the Orange
  River Colony mines was more than 320,000 carats, valued at £938,000.
  But by far the largest of all the pipes hitherto discovered is the
  Premier mine in the Transvaal, about 300 m. to the east of Kimberley.
  This was discovered in 1902 and occupies an area of about 75 acres. In
  1906 it was being worked as a shallow open mine; but the description
  of the Kimberley methods given above is applicable to the washing
  plant at that time being introduced into the Premier mine upon a very
  large scale. Comparatively few of the pipes which have been discovered
  are at all rich in diamonds, and many are quite barren; some are
  filled with "hard blue" which even if diamantiferous may be too
  expensive to work.

  The most competent S. African geologists believe all these remarkable
  pipes to be connected with volcanic outbursts which occurred over the
  whole of S. Africa during the Cretaceous period (after the deposition
  of the Stormberg beds), and drilled these enormous craters through all
  the later formations. With the true pipes are associated dykes and
  fissures also filled with diamantiferous blue ground. It is only in
  the more northerly part of the country that the pipes are filled with
  blue ground (or "kimberlite"), and that they are diamantiferous; but
  over a great part of Cape Colony have been discovered what are
  probably similar pipes filled with agglomerates, breccias and tuffs,
  and some with basic lavas; one, in particular, in the Riversdale
  Division near the southern coast, being occupied by a melilite-basalt.
  It is quite clear that the occurrence of the diamond in the S. African
  pipes is quite different from the occurrences in alluvial deposits
  which have been described above. The question of the origin of the
  diamond in S. Africa and elsewhere is discussed below.

  The River Diggings on the Vaal river are still worked upon a small
  scale, but the production from this source is so limited that they are
  of little account in comparison with the mines in the blue ground. The
  stones, however, are good; since they differ somewhat from the
  Kimberley crystals it is probable that they were not derived from the
  present pipes. Another S. African locality must be mentioned;
  considerable finds were reported in 1905 and 1906 from gravels at
  Somabula near Gwelo in Rhodesia where the diamond is associated with
  chrysoberyl, corundum (both sapphire and ruby), topaz, garnet,
  ilmenite, staurolite, rutile, with pebbles of quartz, granite,
  chlorite-schist, &c. Diamond has also been reported from kimberlite
  "pipes" in Rhodesia.

  _Other Localities._--In addition to the South American localities
  mentioned above, small diamonds have also been mined since their
  discovery in 1890 on the river Mazaruni in British Guiana, and finds
  have been reported in the gold washings of Dutch Guiana. Borneo has
  possessed a diamond industry since the island was first settled by the
  Malays; the references in the works of Garcia de Orta, Linschoten, De
  Boot, De Laet and others, to Malacca as a locality relate to Borneo.
  The large Borneo stone, over 360 carats in weight, known as the Matan,
  is in all probability not a diamond. The chief mines are situated on
  the river Kapuas in the west and near Bandjarmassin in the south-east
  of the island, and the alluvial deposits in which they occur are
  worked by a small number of Chinese and Malays. Australia has yielded
  diamonds in alluvial deposits near Bathurst (where the first discovery
  was made in 1851) and Mudgee in New South Wales, and also near Bingara
  and Inverell in the north of the colony. At Mount Werong a stone
  weighing 29 carats was found in 1905. At Ruby Hill near Bingara they
  were found in a breccia filling a volcanic pipe. At Ballina, in New
  England, diamonds have been found in the sea sand. Other Australian
  localities are Echunga in South Australia; Beechworth, Arena and
  Melbourne in Victoria; Freemantle and Nullagine in Western Australia;
  the Palmer and Gilbert rivers in Queensland. These have been for the
  most part discoveries in alluvial deposits of the goldfields, and the
  stones were small. In Tasmania also diamonds have been found in the
  Corinna goldfields. Europe has produced few diamonds. Humboldt
  searched for them in the Urals on account of the similarity of the
  gold and platinum deposits to those of Brazil, and small diamonds were
  ultimately found (1829) in the gold washings of Bissersk, and later at
  Ekaterinburg and other spots in the Urals. In Lapland they have been
  found in the sands of the Pasevig river. Siberia has yielded isolated
  diamonds from the gold washings of Yenisei. In North America a few
  small stones have been found in alluvial deposits, mostly auriferous,
  in Georgia, N. and S. Carolina, Kentucky, Virginia, Tennessee,
  Wisconsin, California, Oregon and Indiana. A crystal weighing 23¾
  carats was found in Virginia in 1855, and one of 21¼ carats in
  Wisconsin in 1886. In 1906 a number of small diamonds were discovered
  in an altered peridotite somewhat resembling the S. African blue
  ground, at Murfreesboro, Pike county, Arkansas. Considerable interest
  attaches to the diamonds found in Wisconsin, Michigan and Ohio near
  the Great Lakes, for they are here found in the terminal moraines of
  the great glacial sheet which is supposed to have spread southwards
  from the region of Hudson Bay; several of the drift minerals of the
  diamantiferous region of Indiana have been identified as probably of
  Canadian origin; no diamonds have however yet been found in the
  intervening country of Ontario. A rock similar to the blue ground of
  Kimberley has been found in the states of Kentucky and New York. The
  occurrence of diamond in meteorites is described below.

  _Origin of the Diamond in Nature._--It appears from the foregoing
  account that at most localities the diamond is found in alluvial
  deposits probably far from the place where it originated. The minerals
  associated with it do not afford much clue to the original conditions;
  they are mostly heavy minerals derived from the neighbouring rocks, in
  which the diamond itself has not been observed. Among the commonest
  associates of the diamond are quartz, topaz, tourmaline, rutile,
  zircon, magnetite, garnet, spinel and other minerals which are common
  accessory constituents of granite, gneiss and the crystalline schists.
  Gold (also platinum) is a not infrequent associate, but this may only
  mean that the sands in which the diamond is found have been searched
  because they were known to be auriferous; also that both gold and
  diamond are among the most durable of minerals and may have survived
  from ancient rocks of which other traces have been lost.

  The localities at which the diamond has been supposed to occur in its
  original matrix are the following:--at Wajra Karur, in the Cuddapah
  district, India, M. Chaper found diamond with corundum in a decomposed
  red pegmatite vein in gneiss. At S[=a]o João da Chapada, in Minas
  Geraes, diamonds occur in a clay interstratified with the itacolumite,
  and are accompanied by sharp crystals of rutile and haematite in the
  neighbourhood of decomposed quartz veins which intersect the
  itacolumite. It has been suggested that these three minerals were
  originally formed in the quartz veins. In both these occurrences the
  evidence is certainly not sufficient to establish the presence of an
  original matrix. At Inverell in New South Wales a diamond (1906) has
  been found embedded in a hornblende diabase which is described as a
  dyke intersecting the granite. Finally there is the remarkable
  occurrence in the blue ground of the African pipes.

  There has been much controversy concerning the nature and origin of
  the blue ground itself; and even granted that (as is generally
  believed) the blue ground is a much serpentinized volcanic breccia
  consisting originally of an olivine-bronzite-biotite rock (the
  so-called kimberlite), it contains so many rounded and angular
  fragments of various rocks and minerals that it is difficult to say
  which of them may have belonged to the original rock, and whether any
  were formed _in situ_, or were brought up from below as inclusions.
  Carvill Lewis believed the blue ground to be true eruptive rock, and
  the carbon to have been derived from the bituminous shales of which it
  contains fragments. The Kimberley shales, which are penetrated by the
  De Beers group of pipes, were, however, certainly not the source of
  the carbon at the Premier (Transvaal) mine, for at this locality the
  shales do not exist. The view that the diamond may have crystallized
  out from solution in its present matrix receives some support from the
  experiments of W. Luzi, who found that it can be corroded by the
  solvent action of fused blue ground; from the experiments of J.
  Friedländer, who obtained diamond by dissolving graphite in fused
  olivine; and still more from the experiments of R. von Hasslinger and
  J. Wolff, who have obtained it by dissolving graphite in a fused
  mixture of silicates having approximately the composition of the blue
  ground. E. Cohen, who regarded the pipes as of the nature of a mud
  volcano, and the blue ground as a kimberlite breccia altered by
  hydrothermal action, thought that the diamond and accompanying
  minerals had been brought up from deep-seated crystalline schists.
  Other authors have sought the origin of the diamond in the action of
  the hydrated magnesian silicates on hydrocarbons derived from
  bituminous schists, or in the decomposition of metallic carbides.

  Of great scientific interest in this connexion is the discovery of
  small diamonds in certain meteorites, both stones and irons; for
  example, in the stone which fell at Novo-Urei in Penza, Russia, in
  1886, in a stone found at Carcote in Chile, and in the iron found at
  Cañon Diablo in Arizona. Graphitic carbon in cubic form (cliftonite)
  has also been found in certain meteoric "irons," for example in those
  from Magura in Szepes county, Hungary, and Youndegin near York in
  Western Australia. The latter is now generally believed to be altered
  diamond. The fact that H. Moissan has produced the diamond
  artificially, by allowing dissolved carbon to crystallize out at a
  high temperature and pressure from molten iron, coupled with the
  occurrence in meteoric iron, has led Sir William Crookes and others to
  conclude that the mineral may have been derived from deep-seated iron
  containing carbon in solution (see the article GEM, ARTIFICIAL). Adolf
  Knop suggested that this may have first yielded hydrocarbons by
  contact with water, and that from these the crystalline diamond has
  been formed. The meteoric occurrence has even suggested the fanciful
  notion that all diamonds were originally derived from meteorites. The
  meteoric iron of Arizona, some of which contains diamond, is actually
  found in and about a huge crater which is supposed by some to have
  been formed by an immense meteorite penetrating the earth's crust.

  It is, at any rate, established that carbon can crystallize as diamond
  from solution in iron, and other metals; and it seems that high
  temperature and pressure and the absence of oxidizing agents are
  necessary conditions. The presence of sulphur, nickel, &c., in the
  iron appears to favour the production of the diamond. On the other
  hand, the occurrence in meteoric stones, and the experiments mentioned
  above, show that the diamond may also crystallize from a basic magma,
  capable of yielding some of the metallic oxides and ferro-magnesian
  silicates; a magma, therefore, which is not devoid of oxygen. This is
  still more forcibly suggested by the remarkable eclogite boulder found
  in the blue ground of the Newlands mine, not far from the Vaal river,
  and described by T. G. Bonney. The boulder is a crystalline rock
  consisting of pyroxene (chrome-diopside), garnet, and a little
  olivine, and is studded with diamond crystals; a portion of it is
  preserved in the British Museum (Natural History). In another eclogite
  boulder, diamond was found partly embedded in pyrope. Similar boulders
  have also been found in the blue ground elsewhere. Specimens of pyrope
  with attached or embedded diamond had previously been found in the
  blue ground of the De Beers mines. In the Newlands boulder the
  diamonds have the appearance of being an original constituent of the
  eclogite. It seems therefore that a holocrystalline pyroxene-garnet
  rock may be one source of the diamond found in blue ground. On the
  other hand many tons of the somewhat similar eclogite in the De Beers
  mine have been crushed and have not yielded diamond. Further, the
  ilmenite, which is the most characteristic associate of the diamond in
  blue ground, and other of the accompanying minerals, may have come
  from basic rocks of a different nature.

  The Inverell occurrence may prove to be another example of diamond
  crystallized from a basic rock.

  In both occurrences, however, there is still the possibility that the
  eclogite or the basalt is not the original matrix, but may have caught
  up the already formed diamond from some other matrix. Some regard the
  eclogite boulders as derived from deep-seated crystalline rocks,
  others as concretions in the blue ground.

  None of the inclusions in the diamond gives any clue to its origin;
  diamond itself has been found as an inclusion, as have also black
  specks of some carbonaceous materials. Other black specks have been
  identified as haematite and ilmenite; gold has also been found; other
  included minerals recorded are rutile, topaz, quartz, pyrites,
  apophyllite, and green scales of chlorite (?). Some of these are of
  very doubtful identification; others (e.g. apophyllite and chlorite)
  may have been introduced along cracks. Some of the fibrous inclusions
  were identified by H. R. Göppert as vegetable structures and were
  supposed to point to an organic origin, but this view is no longer
  held. Liquid inclusions, some of which are certainly carbon dioxide,
  have also been observed.

  Finally, then, both experiment and the natural occurrence in rocks and
  meteorites suggest that diamond may crystallize not only from iron but
  also from a basic silicate magma, possibly from various rocks
  consisting of basic silicates. The blue ground of S. Africa may be
  the result of the serpentinization of several such rocks, and
  although now both brecciated and serpentinized some of these may have
  been the original matrix. A circumstance often mentioned in support of
  this view is the fact that the diamonds in one pipe generally differ
  somewhat in character from those of another, even though they be near
  neighbours.

_History._--All the famous diamonds of antiquity must have been Indian
stones. The first author who described the Indian mines at all fully was
the Portuguese, Garcia de Orta (1565), who was physician to the viceroy
of Goa. Before that time there were only legendary accounts like that of
Sindbad's "Valley of the Diamonds," or the tale of the stones found in
the brains of serpents. V. Ball thinks that the former legend originated
in the Indian practice of sacrificing cattle to the evil spirits when a
new mine is opened; birds of prey would naturally carry off the flesh,
and might give rise to the tale of the eagles carrying diamonds adhering
to the meat.

The following are some of the most famous diamonds of the world:--

A large stone found in the Golconda mines and said to have weighed 787
carats in the rough, before being cut by a Venetian lapidary, was seen
in the treasury of Aurangzeb in 1665 by Tavernier, who estimated its
weight after cutting as 280 (?) carats, and described it as a rounded
rose-cut-stone, tall on one side. The name _Great Mogul_ has been
frequently applied to this stone. Tavernier states that it was the
famous stone given to Shah Jahan by the emir Jumla. The _Orloff_, stolen
by a French soldier from the eye of an idol in a Brahmin temple, stolen
again from him by a ship's captain, was bought by Prince Orloff for
£90,000, and given to the empress Catharine II. It weighs 194¾ carats,
is of a somewhat yellow tinge, and is among the Russian crown jewels.
The _Koh-i-nor_, which was in 1739 in the possession of Nadir Shah, the
Persian conqueror, and in 1813 in that of the raja of Lahore, passed
into the hands of the East India Company and was by them presented to
Queen Victoria in 1850. It then weighed 186-1/16 carats, but was recut in
London by Amsterdam workmen, and now weighs 106-1/16 carats. There has
been much discussion concerning the possibility of this stone and the
Orloff being both fragments of the Great Mogul. The Mogul Baber in his
memoirs (1526) relates how in his conquest of India he captured at Agra
the great stone weighing 8 mishkals, or 320 ratis, which may be
equivalent to about 187 carats. The Koh-i-nor has been identified by
some authors with this stone and by others with the stone seen by
Tavernier. Tavernier, however, subsequently described and sketched the
diamond which he saw as shaped like a bisected egg, quite different
therefore from the Koh-i-nor. Nevil Story Maskelyne has shown reason for
believing that the stone which Tavernier saw was really the Koh-i-nor
and that it is identical with the great diamond of Baber; and that the
280 carats of Tavernier is a misinterpretation on his part of the Indian
weights. He suggests that the other and larger diamond of antiquity
which was given to Shah Jahan may be one which is now in the treasury of
Teheran, and that this is the true Great Mogul which was confused by
Tavernier with the one he saw. (See Ball, Appendix I. to Tavernier's
_Travels_ (1889); and Maskelyne, _Nature_, 1891, 44, p. 555.).

The _Regent_ or _Pitt_ diamond is a magnificent stone found in either
India or Borneo; it weighed 410 carats and was bought for £20,400 by
Pitt, the governor of Madras; it was subsequently, in 1717, bought for
£80,000 (or, according to some authorities, £135,000) by the duke of
Orleans, regent of France; it was reduced by cutting to 1361-4/16 carats;
was stolen with the other crown jewels during the Revolution, but was
recovered and is still in France. The _Akbar Shah_ was originally a
stone of 116 carats with Arabic inscriptions engraved upon it; after
being cut down to 71 carats it was bought by the gaikwar of Baroda for
£35,000. The _Nizam_, now in the possession of the nizam of Hyderabad,
is supposed to weigh 277 carats; but it is only a portion of a stone
which is said to have weighed 440 carats before it was broken. The
_Great Table_, a rectangular stone seen by Tavernier in 1642 at
Golconda, was found by him to weigh 242-3/16 carats; Maskelyne regards it
as identical with the _Darya-i-nur_, which is also a rectangular stone
weighing about 186 carats in the possession of the shah of Persia.
Another stone, the _Taj-e-mah_, belonging to the shah, is a pale rose
pear-shaped stone and is said to weigh 146 carats.

Other famous Indian diamonds are the following:--The _Sancy_, weighing
531-2/16 carats, which is said to have been successively the property of
Charles the Bold, de Sancy, Queen Elizabeth, Henrietta Maria, Cardinal
Mazarin, Louis XIV.; to have been stolen with the Pitt during the French
Revolution; and subsequently to have been the property of the king of
Spain, Prince Demidoff and an Indian prince. The _Nassak_, 78-5/8 carats,
the property of the duke of Westminster. The _Empress Eugénie_, 51
carats, the property of the gaikwar of Baroda. The _Pigott_, 49
carats(?), which cannot now be traced. The _Pasha_, 40 carats. The
_White Saxon_, 48¾ carats. The _Star of Este_, 251-3/32 carats.

Coloured Indian diamonds of large size are rare; the most famous are:--a
beautiful blue brilliant, 67-2/16 carats, cut from a stone weighing
112-3/16 carats brought to Europe by Tavernier. It was stolen from the
French crown jewels with the Regent and was never recovered. The _Hope_,
44¼ carats, has the same colour and is probably a portion of the missing
stone: it was so-called as forming part of the collection of H. T. Hope
(bought for £18,000), and was sold again in 1906 (resold 1909). Two
other blue diamonds are known, weighing 13¾ and 1¾ carats, which may
also be portions of the French diamond. The _Dresden Green_, one of the
Saxon crown jewels, 40 carats, has a fine apple-green colour. The
_Florentine_, 133-1/5 carats, one of the Austrian crown jewels, is a very
pale yellow.

The most famous Brazilian stones are:--The _Star of the South_, found in
1853, when it weighed 254½ carats and was sold for £40,000; when cut it
weighed 125 carats and was bought by the gaikwar of Baroda for £80,000.
Also a diamond belonging to Mr Dresden, 119 carats before, and 76½
carats after cutting.

Many large stones have been found in South Africa; some are yellow but
some are as colourless as the best Indian or Brazilian stones. The most
famous are the following:--the _Star of South Africa_, or _Dudley_,
mentioned above, 83½ carats rough, 46½ carats cut. The _Stewart_, 288-3/8
carats rough, 120 carats cut. Both these were found in the river
diggings. The _Porter Rhodes_ from Kimberley, of the finest water,
weighed about 150 carats. The _Victoria_, 180 carats, was cut from an
octahedron weighing 457½ carats, and was sold to the nizam of Hyderabad
for £400,000. The _Tiffany_, a magnificent orange-yellow stone, weighs
125½ carats cut. A yellowish octahedron found at De Beers weighed 428½
carats, and yielded a brilliant of 288½ carats. Some of the finest and
largest stones have come from the Jagersfontein mine; one, the
_Jubilee_, found in 1895, weighed 640 carats in the rough and 239 carats
when cut. Until 1905 the largest known diamond in the world was the
_Excelsior_, found in 1893 at Jagersfontein by a native while loading a
truck. It weighed 971 carats, and was ultimately cut into ten stones
weighing from 68 to 13 carats. But all previous records were surpassed
in 1905 by a magnificent stone more than three times the size of any
known diamond, which was found in the yellow ground at the newly
discovered Premier mine in the Transvaal. This extraordinary diamond
weighed 3025¾ carats (11/3 lb.) and was clear and water white; the
largest of its surfaces appeared to be a cleavage plane, so that it
might be only a portion of a much larger stone. It was known as the
_Cullinan Diamond_. This stone was purchased by the Transvaal government
in 1907 and presented to King Edward VII. It was sent to Amsterdam to be
cut, and in 1908 was divided into nine large stones and a number of
small brilliants. The four largest stones weigh 516½ carats, 309-3/16
carats, 92 carats and 62 carats respectively. Of these the first and
second are the largest brilliants in existence. All the stones are
flawless and of the finest quality.

  BIBLIOGRAPHY.--Boetius de Boot, _Gemmarum et lapidum historia_ (1609);
  D. Jeffries, _A Treatise on Diamonds and Pearls_ (1757); J. Mawe,
  _Travels in the Interior of Brazil_ (1812); _Treatise on Diamonds and
  Precious Stones_ (1813): Pinder, _De adamante_ (1829); Murray, _Memoir
  on the Nature of the Diamond_ (1831); C. Zerenner, _De adamante
  dissertatio_ (1850); H. Emanuel, _Diamonds and Precious Stones_
  (1865); A. Schrauf, _Edelsteinkunde_ (1869); N. Jacobs and N.
  Chatrian, _Monographie du diamant_ (1880); V. Ball, _Geology of India_
  (1881); C. W. King, _The Natural History of Precious Stones_ _and
  Precious Metals_ (1883); M. E. Boutan, _Le Diamant_ (1886); S. M.
  Burnham, _Precious Stones in Nature, Art and Literature_ (1887); P.
  Groth, _Grundriss der Edelsteinkunde_ (1887); A. Liversidge, _The
  Minerals of New South Wales_ (1888); _Tavernier's Travels in India_,
  translated by V. Ball (1889); E. W. Streeter, _The Great Diamonds of
  the World_ (1896); H. C. Lewis, _The Genesis and Matrix of the
  Diamond_ (1897); L. de Launay, _Les Diamants du Cap_ (1897); C.
  Hintze, _Handbuch der Mineralogie_ (1898); E. W. Streeter, _Precious
  Stones and Gems_ (6th ed., 1898); Dana, _System of Mineralogy_ (1899);
  Kunz and others, _The Production of Precious Stones_ (in annual,
  _Mineral Resources of the United States_); M. Bauer, _Precious Stones_
  (trans. L. J. Spencer, 1904); A. W. Rogers, _An Introduction to the
  Geology of Cape Colony_ (1905); Gardner F. Williams, _The Diamond
  Mines of South Africa_ (revised edition, 1906); George F. Kunz,
  "Diamonds, a study of their occurrence in the United States, with
  descriptions and comparisons of those from all known localities" (U.S.
  Geol. Survey, 1909); P. A. Wagner, _Die Diamantführenden Gesteine
  Südafrikas_ (1909).

  Among papers in scientific periodicals may be mentioned articles by
  Adler, Ball, Baumhauer, Beck, Bonney, Brewster, Chaper, Cohen,
  Crookes, Daubrée, Derby, Des Cloizeaux, Doelter, Dunn, Flight,
  Friedel, Gorceix, Gürich, Goeppert, Harger, Hudleston, Hussak,
  Jannettaz, Jeremejew, de Launay, Lewis, Maskelyne, Meunier, Moissan,
  Molengraaff, Moulle, Rose, Sadebeck, Scheibe, Stelzner, Stow. See
  generally Hintze's _Handbuch der Mineralogie_. (H. A. MI.)


FOOTNOTE:

  [1] Diamonds are invariably weighed in carats and in ½, ¼, 1/8, 1/16,
    1/32, 1/64 of a carat. One (English) carat = 3.17 grains = .2054
    gram. One ounce = 151½ carats. (See CARAT.)




DIAMOND NECKLACE, THE AFFAIR OF THE, a mysterious incident at the court
of Louis XVI. of France, which involved the queen Marie Antoinette. The
Parisian jewellers Boehmer and Bassenge had spent some years collecting
stones for a necklace which they hoped to sell to Madame Du Barry, the
favourite of Louis XV., and after his death to Marie Antoinette. In 1778
Louis XVI. proposed to the queen to make her a present of the necklace,
which cost 1,600,000 livres. But the queen is said to have refused it,
saying that the money would be better spent equipping a man-of-war.
According to others, Louis XVI. himself changed his mind. After having
vainly tried to place the necklace outside of France, the jewellers
attempted again in 1781 to sell it to Marie Antoinette after the birth
of the dauphin. It was again refused, but it was evident that the queen
regretted not being able to acquire it.

At that time there was a personage at the court whom Marie Antoinette
particularly detested. It was the cardinal Louis de Rohan, formerly
ambassador at Vienna, whence he had been recalled in 1774, having
incurred the queen's displeasure by revealing to the empress Maria
Theresa the frivolous actions of her daughter, a disclosure which
brought a maternal reprimand, and for having spoken lightly of Maria
Theresa in a letter of which Marie Antoinette learned the contents.
After his return to France the cardinal was anxious to regain the favour
of the queen in order to obtain the position of prime minister. In March
1784 he entered into relations with a certain Jeanne de St Remy de
Valois, a descendant of a bastard of Henry II., who after many
adventures had married a _soi-disant_ comte de Lamotte, and lived on a
small pension which the king granted her. This adventuress soon gained
the greatest ascendancy over the cardinal, with whom she had intimate
relations. She persuaded him that she had been received by the queen and
enjoyed her favour; and Rohan resolved to use her to regain the queen's
good will. The comtesse de Lamotte assured the cardinal that she was
making efforts on his behalf, and soon announced to him that he might
send his justification to Marie Antoinette. This was the beginning of a
pretended correspondence between Rohan and the queen, the adventuress
duly returning replies to Rohan's notes, which she affirmed to come from
the queen. The tone of the letters became very warm, and the cardinal,
convinced that Marie Antoinette was in love with him, became ardently
enamoured of her. He begged the countess to obtain a secret interview
for him with the queen, and a meeting took place in August 1784 in a
grove in the garden at Versailles between him and a lady whom the
cardinal believed to be the queen herself. Rohan offered her a rose, and
she promised him that she would forget the past. Later a certain Marie
Lejay (renamed by the comtesse "Baronne Gay d'Oliva," the last word
being apparently an anagram of Valoi), who resembled Marie Antoinette,
stated that she had been engaged to play the role of queen in this
comedy. In any case the countess profited by the cardinal's conviction
to borrow from him sums of money destined ostensibly for the queen's
works of charity. Enriched by these, the countess was able to take an
honourable place in society, and many persons believed her relations
with Marie Antoinette, of which she boasted openly and unreservedly, to
be genuine. It is still an unsettled question whether she simply
mystified people, or whether she was really employed by the queen for
some unknown purpose, perhaps to ruin the cardinal. In any case the
jewellers believed in the relations of the countess with the queen, and
they resolved to use her to sell their necklace. She at first refused
their commission, then accepted it. On the 21st of January 1785 she
announced that the queen would buy the necklace, but that not wishing to
treat directly, she left the affair to a high personage. A little while
later Rohan came to negotiate the purchase of the famous necklace for
the 1,600,000 livres, payable in instalments. He said that he was
authorized by the queen, and showed the jewellers the conditions of the
bargain approved in the handwriting of Marie Antoinette. The necklace
was given up. Rohan took it to the countess's house, where a man, in
whom Rohan believed he recognized a valet of the queen, came to fetch
it. Madame de Lamotte had told the cardinal that Marie Antoinette would
make him a sign to indicate her thanks, and Rohan believed that she did
make him a sign. Whether it was so, or merely chance or illusion, no one
knows. But it is certain that the cardinal, convinced that he was acting
for the queen, had engaged the jewellers to thank her; that Boehmer and
Bassenge, before the sale, in order to be doubly sure, had sent word to
the queen of the negotiations in her name; that Marie Antoinette had
allowed the bargain to be concluded, and that after she had received a
letter of thanks from Boehmer, she had burned it. Meanwhile the "comte
de Lamotte" appears to have started at once for London, it is said with
the necklace, which he broke up in order to sell the stones.

When the time came to pay, the comtesse de Lamotte presented the
cardinal's notes; but these were insufficient, and Boehmer complained to
the queen, who told him that she had received no necklace and had never
ordered it. She had the story of the negotiations repeated for her. Then
followed a _coup de théâtre_. On the 15th of August 1785, Assumption
day, when the whole court was awaiting the king and queen in order to go
to the chapel, the cardinal de Rohan, who was preparing to officiate,
was arrested and taken to the Bastille. He was able, however, to destroy
the correspondence exchanged, as he thought, with the queen, and it is
not known whether there was any connivance of the officials, who did not
prevent this, or not. The comtesse de Lamotte was not arrested until the
18th of August, after having destroyed her papers. The police set to
work to find all her accomplices, and arrested the girl Oliva and a
certain Reteaux de Villette, a friend of the countess, who confessed
that he had written the letters given to Rohan in the queen's name, and
had imitated her signature on the conditions of the bargain. The famous
charlatan Cagliostro was also arrested, but it was recognized that he
had taken no part in the affair. The cardinal de Rohan accepted the
parlement of Paris as judges. A sensational trial resulted (May 31,
1786) in the acquittal of the cardinal, of the girl Oliva and of
Cagliostro. The comtesse de Lamotte was condemned to be whipped, branded
and shut up in the Salpetrière. Her husband was condemned, in his
absence, to the galleys for life. Villette was banished.

Public opinion was much excited by this trial. It is generally believed
that Marie Antoinette was stainless in the matter, that Rohan was an
innocent dupe, and that the Lamottes deceived both for their own ends.
People, however, persisted in the belief that the queen had used the
countess as an instrument to satisfy her hatred of the cardinal de
Rohan. Various circumstances fortified this belief, which contributed to
render Marie Antoinette very unpopular--her disappointment at Rohan's
acquittal, the fact that he was deprived of his charges and exiled to
the abbey of la Chaise-Dieu, and finally the escape of the comtesse de
Lamotte from the Salpetrière, with the connivance, as people believed,
of the court. The adventuress, having taken refuge abroad, published
_Mémoires_ in which she accused the queen. Her husband also wrote
_Mémoires_, and lived until 1831, after having, it is said, received
subsidies from Louis XVIII.

  See M. Tourneux, _Marie Antoinette devant l'histoire: Essai
  bibliographique_ (2nd ed., Paris, 1901); Émile Campardon, _Marie
  Antoinette et le procès du collier_ (Paris, 1863); P. Audebert,
  _L'Affaire du collier de la reine, d'après la correspondance inédite
  du chevalier de Pujol_ (Rouen, 1901); F. d'Albini, _Marie Antoinette
  and the Diamond Necklace from another Point of View_ (London, 1900);
  Funck-Brentano, _L'Affaire du collier_ (1903); A. Lang, _Historical
  Mysteries_ (1904). Carlyle's essay on _The Diamond Necklace_ (first
  published in 1837 in _Fraser's Magazine_) is of historical literary
  interest.




DIANA, in Roman mythology, an old Italian goddess, in later times
identified with the Greek Artemis (q.v.). That she was originally an
independent Italian deity is shown by her name, which is the feminine
form of Janus (= Dianus). She is essentially the goddess of the moon and
light generally, and presides over wood, plain and water, the chase and
war. As the goddess of childbirth, she was known, like Juno, by the name
of Lucina, the "bringer to light." As the moon-goddess she was also
identified with Hecate, and invoked as "three-formed" in reference to
the phases of the moon. Her most celebrated shrine was in a grove at
Aricia (whence her title of Nemorensis) near the modern lake of Nemi.
Here she was worshipped side by side with a male deity Virbius, a god of
the forest and the chase. This Virbius was subsequently identified with
Hippolytus, the favourite of Artemis, who was said to have been brought
to life by Aesculapius and conducted by Diana to Aricia (Ovid, _Fasti_,
iii. 263, vi. 731, _Metam._ xv. 497; Virgil, _Aeneid_, vii. 761). A
barbarous custom, perhaps reminiscent of human sacrifice once offered to
her, prevailed in connexion with her ritual here; her priest, called
_Rex Nemorensis_, who was a runaway slave, was obliged to qualify for
office by slaying his predecessor in single combat (Strabo v. p. 239;
Suetonius, _Caligula_, 35). This led to the identification of Diana with
the Tauric Artemis, whose image was said to have been removed by Orestes
to the grove of Aricia (see ARICINI).

After the destruction of Alba Longa this grove was for a long time the
united sanctuary of the neighbouring Latin and Rutulian cities, until at
last it was extinguished beneath the supremacy of Rome. The festival of
the goddess was on the ides (13th) of August, the full moon of the hot
season. She was worshipped with torches, her aid was sought by women
seeking a happy deliverance in childbirth, and many votive offerings
have been found on the site. The worship of Diana was brought to Rome by
Latin plebeians, and hence she was regarded as the protectress of the
lower classes, and especially of slaves. In accordance with this, her
most important temple was that on the Aventine, the chief seat of the
plebeians, founded by Servius Tullius, originally as a sanctuary of the
Latin league (Dion. Halic. iv. 26). No man was allowed to enter the
temple, and on the day of its dedication (August 13) the slaves kept
holiday (Plutarch, _Quaest. Rom._ 100). This Diana was identified with
the sister of Apollo, and at the secular games she was worshipped simply
as Artemis. Another celebrated sanctuary of Diana was that on the slopes
of Mount Tifata near Capua (where she was worshipped under the name of
Tifatina), a sanctuary specially favoured by Sulla and Vespasian. As
Noctiluca ("giving light by night") she had a sanctuary on the Palatine
which was kept illuminated throughout the night (Varro, _L.L._ v. 68).
On the Nemi priesthood see J. G. Frazer, _Golden Bough_.




DIANA MONKEY, a West African representative of the guenon monkeys taking
its name, _Cercopithecus diana_, from the presence of a white crescent
on the forehead; another characteristic feature being the pointed white
beard. The general colour of the fur is greyish, with a deep tinge of
chestnut from the middle of the back to the root of the tail. Together
with _C. neglectus_ of East and Central Africa, _C. ignitus_ of Liberia,
and _C. roloway_ of the Gold Coast, the diana represents the special
subgenus of guenons known as _Pogonocebus_. Although the diana monkey is
commonly seen in menageries, little is known of its habits in the wild
state.




DIANE DE FRANCE (1538-1619), duchess of Montmorency and Angoulême, was
the natural daughter of Henry II. of France and a young Piedmontese,
Filippe Duc. The constable de Montmorency went so far as to assert that
of all the children of Henry II. Diane was the only one who resembled
him. Catherine de' Medici was greatly incensed at this affront, and took
her revenge by having the constable disgraced on the death of Henry II.
Brantôme is loud in praise of Diane. She was a perfect horsewoman and
dancer, played several musical instruments, knew Spanish and Italian,
and "estoit très belle de visage et de taille." Legitimated in 1547, she
was married in 1553 to Horace Farnese, second son of the duke of Parma,
but her husband was killed soon afterwards at the siege of Hesdin. In
order to assure his position, the constable de Montmorency wished to
marry her to his eldest son, Francis. This was a romantic adventure, for
Francis had clandestinely married Mademoiselle de Piennes. The constable
dissolved this union, and after lengthy negotiations obtained the
dispensation of the pope. On the 3rd of May 1559 Francis married Diane.
A wise and moderate woman, Diane undoubtedly helped to make Francis de
Montmorency one of the leaders of the party of the _politiques_. Again a
widow in 1579, she had some influence at the court of Henry III., and
negotiated his reconciliation with Henry of Navarre (1588). She retained
her influence in the reign of Henry IV., conveyed the bodies of
Catherine de' Medici and Henry III. to St Denis, and died in 1619 at her
hôtel of Angoulême.

  See Brantôme, ed. by Lalanne, in the _Coll de la société d'histoire de
  France_, vol. viii. (1875); J. de Thou, _Historia sui temporis..._
  (1733); Matthieu de Morgues, _Oraison funèbre de Diane de France_
  (Paris, 1619).




DIANE DE POITIERS (1499-1566), duchess of Valentinois, and mistress of
Henry II. of France, was the daughter of Jean de Poitiers, seigneur de
St Vallier, who came of an old family of Dauphiné. In 1515 she married
Louis de Brézé, grand seneschal of Normandy, by whom she had two
daughters. She became a widow in 1533, but soon replaced her husband by
a more illustrious lover, the king's second son, Henry, who became
dauphin in 1536. Although he was ten years younger than Diane, she
inspired the young prince with a profound passion, which lasted until
his death. The accession of Henry II. in 1547 was also the accession of
Diane: she was virtual queen, while Henry's lawful wife, Catherine de'
Medici, lived in comparative obscurity. The part Diane played, however,
must not be exaggerated. More rapacious than ambitious, she concerned
herself little with government, but devoted her energies chiefly to
augmenting her income, and providing for her family and friends. Henry
was the most prodigal of lovers, and gave her all rights over the duchy
of Valentinois. Although she showed great tact in her dealings with the
queen, Catherine drove her from the court after Henry's death, and
forced her to restore the crown jewels and to accept Chaumont in
exchange for Chenonceaux. Diane retired to her château at Anet, where
she died in 1566.

Several historians relate that she had been the mistress of Francis I.
before she became the dauphin's mistress, and that she gave herself to
the king in order to obtain the pardon of her father, who had been
condemned to death as an accomplice of the constable de Bourbon. This
rumour, however, has no serious foundation. Men vied with each other in
celebrating Diane's beauty, which, if we may judge from her portraits,
has been slightly exaggerated. She was a healthy, vigorous woman, and,
by dint of great pains, succeeded in retaining her beauty late into
life. It is said that even on the coldest mornings she would wash her
face with well water. Diane was a patroness of the arts. She entrusted
to Philibert de l'Orme the building of her château at Anet, and it was
for her that Jean Goujon executed his masterpiece, the statue of Diana,
now in the Louvre.

  See G. Guiffrey, _Lettres inédites de Diane de Poytiers_ (Paris, 1866)
  and _Procès criminel de Jehan de Poytiers_ (Paris, 1867); Capefigue,
  _Diane de Poitiers_ (Paris, 1860); Hay, _Madame Dianne de Poytiers_
  (London, 1900).




DIAPASON (Gr. [Greek: dia pasôn], through all), a term in music,
originally for an interval of an octave. The Greek is an abbreviation of
[Greek: hê dia pasôn chordôn symphônia], a consonance through all the
tones of the scale. In this sense it is only used now, loosely, for the
compass of an instrument or voice, or for a harmonious melody. The name
is given to the two foundation stops of an organ, the open and the
stopped diapason (see ORGAN), and to a standard of musical pitch, as in
the French _diapason normal_ (see PITCH, MUSICAL).




DIAPER (derived through the Fr, from the Gr. [Greek: dia], through, and
[Greek: aspros], white; the derivation from the town of Ypres,
"d'Ypres," in Belgium is unhistorical, as diapers were known for
centuries before its existence), the name given to a textile fabric,
formerly of a rich and costly nature with embroidered ornament, but now
of linen or cotton, with a simple woven pattern; and particularly
restricted to small napkins. In architecture, the term "diaper" is given
to any small pattern of a conventional nature repeated continuously and
uniformly over a surface; the designs may be purely geometrical, or
based on floral forms, and in early examples were regulated by the
process of their textile origin. Subsequently, similar patterns were
employed in the middle ages for the surface decoration of stone, as in
Westminster Abbey and Bayeux cathedral in the spandrils of the arcades
of the choir and nave; also in mural painting, stained glass, incised
brasses, encaustic tiles, &c. Probably in most cases the pattern was
copied, so far as the general design is concerned, from the tissues and
stuffs of Byzantine manufacture, which came over to Europe and were
highly prized as ecclesiastical vestments.

[Illustration: A B C]

  In its textile use, the term diaper was originally applied to silk
  patterns of a geometrical pattern; it is now almost exclusively used
  for diamond patterns made from linen or cotton yarns. An illustration
  of two patterns of this nature is shown in the figure. The floats of
  the warp and the weft are mostly in three; indeed the patterns are
  made from a base weave which is composed entirely of floats of this
  number. It will be seen that both designs are formed of what may be
  termed concentric figures--alternately black and white. Pattern B
  differs from pattern A only in that more of these concentric figures
  are used for the complete figure. If pattern B, which shows only one
  unit, were extended, the effect would be similar to A, except for the
  size of the unit. In A there are four complete units, and hence the
  pattern appears more striking. Again, the repeating of B would cause
  the four corner pieces to join and to form a diamond similar to the
  one in the centre. The two diamonds in B would then alternate
  diagonally to left and right. Special names are given to certain kinds
  of diapers, e.g. "bird's-eye," "pheasant's-eye"; these terms indicate,
  to a certain extent, the size of the complete diamond in the
  cloth--the smaller kind taking the name "bird's-eye." The size of the
  pattern on paper has little connexion with the size of the pattern in
  the cloth, for it is clearly the number of threads and picks per inch
  which determine the size of the pattern in the cloth from any given
  design. Although A is larger than what is usually termed the
  "bird's-eye" pattern, it is evident that it may be made to appear as
  such, provided that the cloth is fine enough. These designs, although
  adapted mostly for cloths such as nursery-diapers, for pinafores, &c.,
  are sometimes used in the production of towels and table-cloths. In
  the figure, the first pick in A is identical with the first pick in B,
  and the part C shows how each interweaves with the twenty-four
  threads.




DIAPHORETICS (from Gr. [Greek: diaphorein], to carry through), the name
given to those remedies which promote perspiration. In health there is
constantly taking place an exhalation of watery vapour from the skin, by
which not only are many of the effete products of nutrition eliminated,
but the body is kept cool. Under exertion or in a heated atmosphere this
natural function of the skin is increased, sweating more or less profuse
follows, and, evaporation going on rapidly over the whole surface,
little or no rise in the temperature of the body takes place. In many
forms of disease, such as fevers and inflammatory affections, the
action of the skin is arrested, and the surface of the body feels harsh
and dry, while the temperature is greatly elevated. The occurrence of
perspiration not unfrequently marks a crisis in such diseases, and is in
general regarded as a favourable event. In some chronic diseases, such
as diabetes and some cases of Bright's disease, the absence of
perspiration is a marked feature; while, on the other hand, in many
wasting diseases, such as phthisis, the action of the skin is increased,
and copious exhausting sweating occurs. Many means can be used to induce
perspiration, among the best known being baths, either in the form of
hot vapour or hot water baths, or in that part of the process of the
Turkish bath which consists in exposing the body to a dry and hot
atmosphere. Such measures, particularly if followed by the drinking of
hot liquids and the wrapping of the body in warm clothing, seldom fail
to excite copious perspiration. Numerous medicinal substances have the
same effect.




DIAPHRAGM (Gr. [Greek: diaphragma], a partition). The diaphragm or
midriff (Anglo-Saxon, _mid_, middle, _hrif_, belly) in human anatomy is
a large fibro-muscular partition between the cavities of the thorax and
abdomen; it is convex toward the thorax, concave toward the abdomen, and
consists of a central tendon and a muscular margin. The _central tendon_
(q, fig. 1) is trefoil in shape, its leaflets being right, left and
anterior; of these the right is the largest and the left the smallest.
The fleshy fibres rise, in front from the back of the xiphoid cartilage
of the sternum (d), laterally by six serrations, from the inner surfaces
of the lower six ribs, interdigitating with the transversalis,
posteriorly from the arcuate ligaments, of which there are five, a pair
of external, a pair of internal, and a single median one. The _external
arcuate ligament_ (h) stretches from the tip of the twelfth rib (b) to
the costal process of the first lumbar vertebra in front of the
quadratus lumborum muscle (o), the _internal_ and _middle_ are
continuations of the _crura_ which rise from the ventro-lateral aspects
of the bodies of the lumbar vertebrae, the right (e) coming from three,
the left (f) from two. On reaching the level of the twelfth thoracic
vertebra each crus spreads out into a fan-shaped mass of fibres, of
which the innermost join their fellows from the opposite crus, in front
of the aortic opening (k), to form the _middle arcuate ligament_; the
outer ones (g) arch in front of the psoas muscle (n) to the tip of the
costal process of the first lumbar vertebra to form the _internal
arcuate ligament_, while the intermediate ones pass to the central
tendon. There are three large openings in the diaphragm; the _aortic_
(k) is behind the middle arcuate ligament and transmits the aorta, the
vena azygos major, and the thoracic duct. In the right leaflet is an
opening (sometimes called the _hiatus quadratus_) for the inferior vena
cava and a branch of the right phrenic nerve (m), while in front and a
little to the left of the aortic opening is one for the oesophagus and
the two pneumogastric nerves (l), the left being in front and the right
behind. The fleshy fibres on each side of this opening act as a
sphincter. Passing between the xiphoid and costal origins in front are
the superior epigastric arteries, while the other terminal branches of
the internal mammaries, the musculo-phrenics, pass through between two
costal origins.

[Illustration: FIG. 1.--Abdominal Surface of the Diaphragm.]

Through the crura pass the splanchnic nerves, and in addition to these
the left crus is pierced by the vena azygos minor. The sympathetic
nerves usually enter the abdomen behind the internal arcuate ligaments.
The phrenic nerves, which are the main supply of the diaphragm, divide
before reaching the muscle and pierce it in a number of places to enter
its abdominal surface, but some of the lower intercostal nerves assist
in the supply. The last thoracic or subcostal nerves pass behind the
external arcuate ligament.

For the action of the diaphragm see RESPIRATORY SYSTEM.

  _Embryology._--The diaphragm is at first developed in the neck region
  of the embryo, and this accounts for the phrenic nerves, which supply
  it, rising from the fourth and fifth cervical. From the mesoderm on
  the caudal side of the pericardium is developed the _septum
  transversum_, and in this the central tendon is formed. The fleshy
  portion is developed on each side in two parts, an anterior or
  sterno-costal which is derived from the longitudinal neck musculature,
  probably the same layer from which the sternothyroid comes, and a
  spinal part which is a derivative of the transversalis sheet of the
  trunk. Between these two parts is at one time a gap, the _spino-costal
  hiatus_, and this is obliterated by the growth of the
  pleuro-peritoneal membrane, which may occasionally fail to close and
  so may form the site of a phrenic hernia. With the growth of the body
  and the development of the lungs the diaphragm shifts its position
  until it becomes the septum between the thoracic and abdominal
  cavities. (See A. Keith, "On the Development of the Diaphragm," _Jour.
  of Anat. and Phys._ vol. 39.) A. Paterson has recorded cases in which
  the left half of the diaphragm is wanting (_Proceedings_ of the
  Anatomical Society of Gt. Britain, June 1900; _Jour. of Anat. and
  Phys._ vol. 34), and occasionally deficiencies are found elsewhere,
  especially in the sternal portion. For further details see Quain's
  _Anatomy_, vol. i. (London, 1908).

  _Comparative Anatomy._--A complete diaphragm, separating the thoracic
  from the abdominal parts of the coelom, is characteristic of the
  Mammalia; it usually has the human structure and relations except that
  below the Anthropoids it is separated from the pericardium by the
  azygous lobe of the lung. In some Mammals, e.g. Echidna and Phocoena,
  it is entirely muscular. In the Cetacea it is remarkable for its
  obliquity; its vertebral attachment is much nearer the tail than its
  sternal or ventral one; this allows a much larger lung space in the
  dorsal than in the ventral part of the thorax, and may be concerned
  with the equipoise of the animal. (Otto Müller, "Untersuchungen über
  die Veränderung, welche die Respirationsorgane der Säugetiere durch
  die Anpassung an das Leben im Wasser erlitten haben," _Jen. Zeitschr.
  f. Naturwiss._, 1898, p. 93.) In the Ungulata only one crus is found
  (Windle and Parsons, "Muscles of the Ungulata," _Proc. Zool. Soc._,
  1903, p. 287). Below the Mammals incomplete partitions between the
  pleural and peritoneal cavities are found in Chelonians, Crocodiles
  and Birds, and also in Amphibians (Xenopus and Pipa).     (F. G. P.)




DIARBEKR[1] (_Kara Amid_ or Black Amid; the Roman _Amida_), the chief
town of a vilayet of Asiatic Turkey, situated on a basaltic plateau on
the right bank of the Tigris, which here flows in a deep open valley.
The town is still surrounded by the masonry walls of black basalt which
give it the name of _Kara_ or Black Amid; they are well built and
imposing on the west facing the open country, but almost in ruins where
they overlook the river. A mass of gardens and orchards cover the slope
down to the river on the S.W., but there are no suburbs outside the
walls. The houses are rather crowded but only partially fill the walled
area. The population numbers 38,000, nearly half being Christian,
comprising Turks, Kurds, Arabs, Turkomans, Armenians, Chaldeans,
Jacobites and a few Greeks. The streets are 10 ft. to 15 ft. wide, badly
paved and dirty; the houses and shops are low, mostly of stone, and some
of stone and mud. The bazaar is a good one, and gold and silver filigree
work is made, peculiar in character and design. The cotton industry is
declining, but manufacture of silk is increasing. Fruit is good and
abundant as the rich volcanic soil is well watered from the town
springs. The size of the melons is specially famous. To the south, the
walls are some 40 ft. high, faced with large cut stone blocks of very
solid construction, with towers and square bastions rising to 500 ft.
There are four gates: on the north the Kharput gate, on the west the
Rum, on the south the Mardin, and on the east the Yeni Kapu or new
gate. A citadel enclosure stands at the N. E. corner and is now partly
in ruins, but the interior space is occupied by the government konak.
The summer climate in the confined space within the town is excessively
hot and unhealthy. Epidemics of typhus are not unknown, as well as
ophthalmia. The Diarbekr boil is like the "Aleppo button," lasting a
long time and leaving a deep scar. Winters are frequently severe but do
not last long. Snow sometimes lies, and ice is stored for summer use.
Scorpions noted for the virulence of their poison abound as well as
horse leeches in the tanks. The town is supplied with water both by
springs inside the town and by aqueducts from fountains at Ali Punar and
Hamervat. The principal exports are wool, mohair and copper ore, and
imports are cotton and woollen goods, indigo, coffee, sugar, petroleum,
&c.

The Great Mosque, Ulu Jami, formerly a Christian church, occupies the
site of a Sassanian palace and was built with materials from an older
palace, probably that of Tigranes II. The remains consist of the façades
of two palaces 400 ft. apart, each formed by a row of Corinthian columns
surmounted by an equal number of a Byzantine type. Kufic inscriptions
run across the fronts under the entablature. The court of the mosque is
entered by a gateway on which lions and other animals are sculptured.
The churches of greatest interest are those of SS. Cosmas and Damian
(Jacobite) and the church of St James (Greek). In the 19th century
Diarbekr was one of the largest and most flourishing cities of Asia, and
as a commercial centre it now stands at the meeting-point of several
important routes. It is at the head of the navigation of the Tigris,
which is traversed down stream by _keleks_ or rafts supported by
inflated skins. There is a good road to Aleppo and Alexandretta on the
Mediterranean, and to Samsun on the Black Sea by Kharput, Malatia and
Sivas. There are also routes to Mosul and Bitlis.

Diarbekr became a Roman colony in A.D. 230 under the name of Amida, and
received a Christian bishop in A.D. 325. It was enlarged and
strengthened by Constantius II., in whose reign it was taken after a
long siege by Shapur (Sapor) II., king of Persia. The historian Ammianus
Marcellinus, who took part in the defence, gives a detailed account of
it. In the later wars between the Persians and Romans it more than once
changed hands. Though ceded by Jovian to the Persians it again became
annexed to the Roman empire, and in the reign of Anastasius (A.D. 502)
was once more taken by the Persians, when 80,000 of its inhabitants were
slain. It was taken c. 638 by the Arabs, and afterwards passed into the
hands of the Seljuks and Persians, from whom it was finally captured by
Selim I. in 1515; and since that date it has remained under Ottoman
rule. About 2 m. below the town is a masonry bridge over the Tigris; the
older portion being probably Roman, and the western part, which bears a
Kufic inscription, being Arab.

The vilayet of Diarbekr extends south from Palu on the Euphrates to
Mardin and Nisibin on the edge of the Mesopotamian plain, and is divided
into three sanjaks--Arghana, Diarbekr and Mardin. The headwaters of the
main arm of the Tigris have their source in the vilayet.

Cereals, cotton, tobacco, rice and silk are produced, but most of the
fertile lands have been abandoned to semi-nomads, who raise large
quantities of live stock. The richest portion of the vilayet lies east
of the capital in the rolling plains watered by tributaries of the
Tigris. An exceptionally rich copper mine exists at Arghana Maden, but
it is very imperfectly worked; galena mineral oil and silicious sand are
also found.     (C. W. W.; F. R. M.)


FOOTNOTE:

  [1] From _Diar_, land, and Bekr (i.e. Abu Bekr, the caliph).




DIARRHOEA (from Gr. [Greek: dia], through, [Greek: rheô], flow), an
excessive looseness of the bowels, a symptom of irritation which may be
due to various causes, or may be associated with some specific disease.
The treatment in such latter cases necessarily varies, since the symptom
itself may be remedial, but in ordinary cases depends on the removal of
the cause of irritation by the use of aperients, various sedatives being
also prescribed. In chronic diarrhoea careful attention to the diet is
necessary.




DIARY, the Lat. _diarium_ (from _dies_, a day), the book in which are
preserved the daily memoranda regarding events and actions which come
under the writer's personal observation, or are related to him by
others. The person who keeps this record is called a diarist. It is not
necessary that the entries in a diary should be made each day, since
every life, however full, must contain absolutely empty intervals. But
it is essential that the entry should be made during the course of the
day to which it refers. When this has evidently not been done, as in the
case of Evelyn's diary, there is nevertheless an effort made to give the
memoranda the effect of being so recorded, and in point of fact, even in
a case like that of Evelyn, it is probable that what we now read is an
enlargement of brief notes jotted down on the day cited. When this is
not approximately the case, the diary is a fraud, for its whole value
depends on its instantaneous transcript of impressions.

In its primitive form, the diary must always have existed; as soon as
writing was invented, men and women must have wished to note down, in
some almanac or journal, memoranda respecting their business, their
engagements or their adventures. But the literary value of these would
be extremely insignificant until the spirit of individualism had crept
in, and human beings began to be interesting to other human beings for
their own sake. It is not, therefore, until the close of the Renaissance
that we find diaries beginning to have literary value, although, as the
study of sociology extends, every scrap of genuine and unaffected record
of early history possesses an ethical interest. In the 17th century,
diaries began to be largely written in England, although in most cases
without any idea of even eventual publication. Sir William Dugdale
(1605-1686) had certainly no expectation that his slight diary would
ever see the light. There is no surviving record of a journal kept by
Clarendon, Richard Baxter, Lucy Hutchinson and other autobiographical
writers of the middle of the century, but we may take it for granted
that they possessed some such record, kept from day to day. Bulstrode
Whitelocke (1605-1675), whose _Memorials of the English Affairs_ covers
the ground from 1625 to 1660, was a genuine diarist. So was the elder
George Fox (1624-1690), who kept not merely "a great journal," but "the
little journal books," and whose work was published in 1694. The famous
diary of John Evelyn (1620-1706) professes to be the record of seventy
years, and, although large tracts of it are covered in a very
perfunctory manner, while in others many of the entries have the air of
having been written in long after the event, this is a very interesting
and amusing work; it was not published until 1818. In spite of all its
imperfections there is a great charm about the diary of Evelyn, and it
would hold a still higher position in the history of literature than it
does if it were not overshadowed by what is unquestionably the most
illustrious of the diaries of the world, that of Samuel Pepys
(1633-1703). This was begun on the 1st of January 1660 and was carried
on until the 29th of May 1669. The extraordinary value of Pepys' diary
consists in its fidelity to the portraiture of its author's character.
He feigns nothing, conceals nothing, sets nothing down in malice or
insincerity. He wrote in a form of shorthand intelligible to no one but
himself, and not a phrase betrays the smallest expectation that any eye
but his own would ever investigate the pages of his confession. The
importance of this wonderful document, in fact, lay unsuspected until
1819, when the Rev. John Smith of Baldock began to decipher the MS. in
Magdalene College, Cambridge. It was not until 1825 that Lord Braybrooke
published part of what was only fully edited, under the care of Mr
Wheatley, in 1893-1896. In the age which succeeded that of Pepys, a
diary of extraordinary emotional interest was kept by Swift from 1710 to
1713, and was sent to Ireland in the form of a "Journal to Stella"; it
is a surprising amalgam of ambition, affection, wit and freakishness.
John Byrom (1692-1763), the Manchester poet, kept a journal, which was
published in 1854. The diary of the celebrated dissenting divine, Philip
Doddridge (1702-1751), was printed in 1829. Of far greater interest are
the admirably composed and vigorously written journals of John Wesley
(1703-1791). But the most celebrated work of this kind produced in the
latter half of the 18th century was the diary of Fanny Burney (Madame
D'Arblay), published in 1842-1846. It will be perceived that, without
exception, these works were posthumously published, and the whole
conception of the diary has been that it should be written for the
writer alone, or, if for the public, for the public when all prejudice
shall have passed away and all passion cooled down. Thus, and thus only,
can the diary be written so as to impress upon its eventual readers a
sense of its author's perfect sincerity and courage.

Many of the diaries described above were first published in the opening
years of the 19th century, and it is unquestionable that the interest
which they awakened in the public led to their imitation. Diaries ceased
to be rare, but as a rule the specimens which have hitherto appeared
have not presented much literary interest. Exception must be made in
favour of the journals of two minor politicians, Charles Greville
(1794-1865) and Thomas Creevey (1768-1838), whose indiscretions have
added much to the gaiety of nations; the papers of the former appeared
in 1874-1887, those of the latter in 1903. The diary of Henry Crabb
Robinson (1775-1867), printed in 1869, contains excellent biographical
material. Tom Moore's journal, published in 1856 by Lord John Russell,
disappointed its readers. But it is probable, if we reason by the
analogy of the past, that the most curious and original diaries of the
19th century are still unknown to us, and lie jealously guarded under
lock and key by the descendants of those who compiled them.

It was natural that the form of the diary should appeal to a people so
sensitive to social peculiarities and so keen in the observation of them
as the French. A medieval document of immense value is the diary kept by
an anonymous _curé_ during the reigns of Charles VI. and Charles VII.
This _Journal d'un bourgeois de Paris_ was kept from 1409 to 1431, and
was continued by another hand down to 1449. The marquis de Dangeau
(1638-1720) kept a diary from 1684 till the year of his death; this
although dull, and as Saint-Simon said "of an insipidity to make you
sick," is an inexhaustible storehouse of facts about the reign of Louis
XIV. Saint-Simon's own brilliant memoirs, written from 1691 to 1723, may
be considered as a sort of diary. The lawyer, Edmond Barbier
(1689-1771), wrote a journal of the anecdotes and little facts which
came to his knowledge from 1718 to 1762. The studious care which he took
to be correct, and his manifest candour, give a singular value to
Barbier's record; his diary was not printed at all until 1847, nor, in
its entirety, until 1857. The song-writer, Charles Collé (1709-1783),
kept a _journal historique_ from 1758 to 1782; it is full of vivacity,
but very scandalous and spiteful. It saw the light in 1805, and
surprised those to whom Collé, in his lifetime, had seemed the most
placid and good-natured of men. Petit de Bachaumont (1690-1770) had
access to remarkable sources of information, and his _Mémoires secrets_
(a diary the publication of which began in 1762 and was continued after
Bachaumont's death, until 1787, by other persons) contains a valuable
mass of documents. The marquis d'Argenson (1694-1757) kept a diary, of
which a comparatively full text was first published in 1859. In recent
times the posthumous publication of the diaries of the Russian artist,
Marie Bashkirtseff (1860-1884), produced a great sensation in 1887, and
revealed a most remarkable temperament. The brothers Jules and Edmond de
Goncourt kept a very minute diary of all that occurred around them in
artistic and literary Paris; after the death of Jules, in 1870, this was
continued by Edmond, who published the three first volumes in 1888. The
publication of this work was continued, and it produced no little
scandal. It is excessively ill-natured in parts, but of its vivid
picturesqueness, and of its general accuracy as a transcript of
conversation, there can be no two opinions.     (E. G.)




DIASPORE, a native aluminium hydroxide, AlO(OH), crystallizing in the
orthorhombic system and isomorphous with göthite and manganite. It
occurs sometimes as flattened crystals, but usually as lamellar or scaly
masses, the flattened surface being a direction of perfect cleavage on
which the lustre is markedly pearly in character. It is colourless or
greyish-white, yellowish, sometimes violet in colour, and varies from
translucent to transparent. It may be readily distinguished from other
colourless transparent minerals, with a perfect cleavage and pearly
lustre--mica, talc, brucite, gypsum--by its greater hardness of 6½-7.
The specific gravity is 3.4. When heated before the blowpipe it
decrepitates violently, breaking up into white pearly scales; it was
because of this property that the mineral was named diaspore by R. J.
Hauy in 1801, from [Greek: diaspeirein], "to scatter." The mineral
occurs as an alteration product of corundum or emery, and is found in
granular limestone and other crystalline rocks. Well-developed crystals
are found in the emery deposits of the Urals and at Chester,
Massachusetts, and in kaolin at Schemnitz in Hungary. If obtainable in
large quantity it would be of economic importance as a source of
alumina.     (L. J. S)




DIASTYLE (from Gr. [Greek: dia], through, and [Greek: stylos], column),
in architecture, a term used to designate an intercolumniation of three
or four diameters.




DIATOMACEAE. For the knowledge we possess of these beautiful plants, so
minute as to be undiscernible by our unaided vision, we are indebted to
the assistance of the microscope. It was not till towards the close of
the 18th century that the first known forms of this group were
discovered by O. F. Muller. And so slow was the process of discovery in
this field of scientific research that in the course of half a century,
when Agardh published his _Systema algarum_ in 1824, only forty-nine
species included under eight genera had been described. Since that time,
however, with modern microscopes and microscopic methods, eminent
botanists in all parts of the civilized world have studied these minute
plants, with the result that the number of known genera and species has
been greatly increased. Over 10,000 species of diatoms have been
described, and about 1200 species and numerous varieties occur in the
fresh waters and on the coasts of Great Britain and Ireland. Rabenhorst,
in the index to his _Flora Europaea algarum_ (1864) enumerated about
4000 forms which had up to that time been discovered throughout the
continent of Europe.

[Illustration: FIG. 1. A and B, _Melosira arenaria._ C-E, _Melosira
varians._ E, showing formation of auxospore.]

[Illustration: FIG. 2.--_Synedra Ulna._]

The diatoms are more commonly known among systematic botanists as the
Bacillarieae, particularly on the continent of Europe, and although such
an immense number of very diverse forms are included in it, the group as
a whole exhibits a remarkable uniformity of structure. The Bacillarieae
is one of the large groups of Algae, placed by some in close proximity
to the Conjugatae and by others as an order of the Brown Algae (or
Phaeophyceae), but their characters are so distinctive and their
structure is so uniform as to warrant the separation of the diatoms as a
distinct class. The affinities of the group are doubtful.

The diatoms exhibit great variety of form. While some species are
circular and more or less disk-shaped, others are oval in outline. Some
are linear, as _Synedra Ulna_ (fig. 2), others more or less crescentic;
others again are cuneate, as _Podosphenia Lyngbyii_ (fig. 3); some few
have a sigmoid outline, as _Pleurosigma balticum_ (fig. 4); but the
prevailing forms are naviculoid, as in the large family Naviculaceae, of
which the genus _Navicula_ embraces upwards of 1000 species. They vary
also in their modes of growth,--some being free-floating, others
attached to foreign bodies by simple or branched gelatinous stalks,
which in some species are short and thick, while in others they are long
and slender. In some genera the forms are simple, while in others the
frustules are connected together in ribbon-like filaments, or form, as
in other cases, zigzag chains. In some genera the individuals are naked,
while in many others they are enclosed in a more or less definite
gelatinous investment. The conditions necessary to their growth are
moisture and light. Wherever these circumstances coexist, diatomaceous
forms will almost invariably be found. They occur mixed with other
organisms on the surface of moist rocks; in streamlets and pools, they
form a brownish stratum on the surface of the mud, or cover the stems
and leaves of water plants or floating twigs with a furry investment.
Marine forms are usually attached to various sea-weeds, and many are
found in the stomachs of molluscs, holothurians, ascidians and other
denizens of the ocean. The fresh-water forms are specifically distinct
from those incidental to salt or brackish water,--fresh-water species,
however, are sometimes carried some distance into the sea by the force
of the current, and in tidal rivers marine forms are carried up by the
force of the tide. Some notion may be formed of the extreme minuteness
of these forms from the fact that one the length of which is 1/200th of
an inch may be considered as beyond the medium size. Some few, indeed,
are much larger, but by far the greater proportion are of very much
smaller dimensions.

[Illustration: FIG. 3.--_Podosphenia Lyngbyii._]

[Illustration: FIG. 4.--_Pleurosigma balticum._]

[Illustration: FIG. 5. A-C, _Tetracyclus lacustris._ D and E,
_Tabellaria fenestrata._ F and G, _Tabellaria flocculosa._]

Diatoms are unicellular plants distinguished from kindred forms by the
fact of having their soft vegetative part covered by a siliceous case.
Each individual is known as a frustule, and the cell-wall consists of
two similar valves nearly parallel to each other, each valve being
furnished with a rim (or connecting-band) projecting from it at a right
angle.

One of these valves with its rim is slightly smaller than the other,
the smaller fitting into the larger pretty much as a pill-box fits into
its cover. This peculiarity of structure affords ample scope for the
growth of the protoplasmic cell-contents, for as the latter increase in
volume the siliceous valves are pushed out, and their corresponding
siliceous rims become broader. The connecting-bands although closely
fitting their respective valves are distinct from them, and together the
two bands form the girdle.

An individual diatom is usually described from two aspects, one in which
the surface of the valve is exposed to view--the valve view, and one in
which the girdle side is exposed--the girdle view. The valves are thin
and transparent, convex on the outside, and generally ornamented with a
variety of sculptured markings. These sculptures often present the
aspect of striae across the face of the valve, and the best lenses have
shown them to consist of a series of small cavities within the siliceous
wall of the cell. The valves of some of the marine genera exhibit a
beautiful areolated structure due to the presence of larger chambers
within the siliceous cell-wall. Many diatoms possess thickenings of the
cell-wall, visible in the valve view, in the centre of the valve and at
each extremity. These thickenings are known as the nodules, and they are
generally connected by a long median line, the raphe, which is a cleft
in the siliceous valve, extending at least some part of its length.

The protoplasmic contents of this siliceous box-like unicell are very
similar to the contents of many other algal cells. There is a living
protoplasmic layer or primordial utricle, connected either by two broad
bands or by a number of anastomosing threads with a central mass of
protoplasm in which the nucleus is embedded. The greater part of the
cavity of the cell is occupied by one or several fluid vacuoles. The
characteristic brown colour of diatoms is due to the presence of
chromatophores embedded in the lining layer of protoplasm. In number and
form these chromatophores are variable. They contain chlorophyll, but
the green colour is masked by the presence of diatomin, a brown pigment
which resembles that which occurs in the Brown Algae or Phaeophyceae.
The chromatophores contain a variable number of pyrenoids, colourless
proteid bodies of a crystalloidal character.

One of the first phenomena which comes under the notice of the observer
is the extraordinary power of motion with which the frustules are
endowed. Some species move slowly backwards and forwards in pretty much
the same line, but in the case of _Bacillaria paradoxa_ the motion is
very rapid, the frustules darting through the water in a zigzag course.
To account for this motion various theories have been suggested, none of
which appear to be altogether satisfactory. There is little doubt that
the movements are connected with the raphe, and in some diatoms there is
much evidence to prove that they are due to an exudation of mucilage.

_Classification._--The most natural system of classification of the
Bacillarieae is the one put forward by Schütt (1896), and since
generally followed by systematists. He separates them into two primary
divisions, the 'Centricae' and the 'Pennatae.' The former includes all
those diatoms which in the valve view possess a radial symmetry around a
central point, and which are destitute of a raphe (or a pseudoraphe).
The latter includes those which are zygomorphic or otherwise irregular,
and in which the valve view is generally boat-shaped or needle-shaped,
with the markings arranged in a sagittal manner on each side of a raphe
or pseudoraphe.

_Reproduction._--In the Diatomaceae, as well as in the Desmidieae, the
ordinary mode of increase is by simple cell-division. The cell-contents
within the enclosure of the siliceous case separate into two distinct
masses. As these two daughter-masses become more and more developed, the
valves of the mother-cell are pushed more and more widely apart. A new
siliceous valve is secreted by each of the two masses on the side
opposite to the original valve, the new valves being situated within the
girdle of the original frustule. When this process has been completed
the girdle of the mother frustule gives way, and two distinct frustules
are formed, the siliceous valves in each of these new frustules being
one of the valves of the mother-cell, and a newly formed valve similar
and more or less parallel to it.

During the life of the plant this process of self-division is continued
with an almost incredible rapidity. On this subject the observation of
Professor William Smith, writing in 1853, is worthy of special
notice:--"I have been unable to ascertain the time occupied in a single
act of self-division, but supposing it to be completed in twenty-four
hours we should have, as the progeny of a single frustule, the amazing
number of 1,000,000,000 in a single month, a circumstance which will in
some degree explain the sudden, or at least rapid, appearance of these
organisms in localities where they were a short time previously either
unrecognized or sparingly diffused" (_British Diatomaceae_, vol. i. p.
25).

[Illustration: FIG. 6.--Formation of Auxospores.

  A. _Navicula limosa._
  B. _Achnanthes flexella._
  C. _Navicula Amphisbaena._
  D. _Navicula viridis._]

Individual diatoms when once produced by cell-division are incapable of
any increase in size owing to the rigidity of their siliceous
cell-walls, and since the new valves are always formed _within_ the
girdle of the old ones, it would follow that every succeeding generation
is reduced in size by the thickness of the girdle. In some diatoms,
however, this is not strictly true as daughter-cells are sometimes
produced of larger size than the parent-cells. Thus, the reduction in
size of the individuals is not always proportionate to the number of
cell-divisions.

On the diminution in size having reached a limit in any species, the
maximum size is regained by the formation of an auxospore. There are
five known methods of reproduction by auxospores, but it is unnecessary
here to enter into details of these methods. Suffice it to say that a
normal auxospore is produced by the conjugation of two parent-cells, its
distinguishing feature being a rejuvenescence accompanied by a marked
increase in size. These auxospores formed without conjugation are
parthenogenetic.

_Mode of Preparation._--The Diatomaceae are usually gathered in small
bottles, and special care should be taken to collect them as free as
possible from extraneous matter. A small portion having been examined
under the microscope, should the gathering be thought worthy of
preservation, some of the material is boiled in acid for the purpose of
cleaning it. The acids usually employed are hydrochloric, nitric or
sulphuric, according as circumstances require. When the operator
considers that by this process all foreign matter has been eliminated,
the residuum is put into a precipitating jar of a conical shape, broader
at the bottom than at the top, and covered to the brim with filtered or
distilled water. When the diatoms have settled in the bottom of the jar,
the supernatant fluid is carefully removed by a syringe or some similar
instrument, so that the sediment be not disturbed. The jar is again
filled with water, and the process repeated till the acid has been
completely removed. It is desirable afterwards to boil the sediment for
a short time with supercarbonate of soda, the alkali being removed in
the same manner as the acid. A small portion may then be placed with a
pipette upon a slip of glass, and, when the moisture has been thoroughly
evaporated, the film that remains should be covered with dilute Canada
balsam, and, a thin glass cover having been gently laid over the balsam,
the preparation should be laid aside for a short time to harden, and
then is ready for observation.

_General Remarks._--Diatoms are most abundant in cold latitudes, having
a general preference for cold water. In the pelagic waters of lakes and
of the oceans they are often very abundant, and in the cold waters of
the Arctic and Antarctic Oceans they exist in prodigious numbers. They
thus form a large proportion of both the marine and the fresh-water
plankton.

Large numbers of fossil diatoms are known. Not only are these minute
plants assisting at the present time in the accumulation of oceanic and
lake deposits, but in former ages they have been sufficiently active to
give rise to considerable deposits of diatomaceous earths. When the
plant has fulfilled its natural course the siliceous covering sinks to
the bottom of the water in which it had lived, and there forms part of
the sediment. When in the process of ages, as it has often happened, the
accumulated sediment has been hardened into solid rock, the siliceous
frustules of the diatoms remain unaltered, and, if the rock be
disintegrated by natural or artificial means, may be removed from the
enveloping matrix and subjected to examination under the microscope. The
forms found may from their character help in some degree to illustrate
the conditions under which the stratum of rock had been originally
deposited. These earths are generally of a white or grey colour. Some of
them are hard, but most are soft and friable. Many of them are of
economic importance, being used as polishing powders ("Tripoli"), as
absorbents for nitroglycerin in the manufacture of dynamite
("Kieselguhr"), as a dentifrice, and more recently they have been used
to a large extent in the manufacture of non-conducting and sound-proof
materials. Most of these diatomaceous earths are associated with rocks
of Tertiary formations, although it is generally regarded that the
earliest appearance of diatoms is in the Upper Cretaceous (chalk).

Vast deposits of Diatomaceous earths have been discovered in various
parts of the world,--some the deposit of fresh, others of salt water. Of
these deposits the most remarkable for extent, as well as for the number
and beauty of the species contained in it, is that of Richmond, in
Virginia, one of the United States of America. It extends for many
miles, and is in some places at least 40 ft. deep. It is a remarkable
fact that though the generations of a diatom in the space of a few
months far exceed in number the generation of man during the period
usually assigned to the existence of the race, the fossil genera and
species are in most respects to the most minute details identical with
the numerous living representatives of their class.
     (E. O'M.; G. S. W.*)




DIAULOS (from Gr. [Greek: di-], double, and [Greek: aulos], pipe), in
architecture, the peristyle round the great court of the palaestra,
described by Vitruvius (v. II), which measured two stadia (1200 ft.) in
length; on the south side this peristyle had two rows of columns, so
that in stormy weather the rain might not be driven into the inner part.
The word was also used in ancient Greece for a foot-race of twice the
usual length.




DIAVOLO, FRA (1771-1806), the popular name given to a famous Italian
brigand associated with the political revolutions of southern Italy at
the time of the French invasion. His real name was Michele Pezza, and he
was born of low parentage at Itri; he had committed many murders and
robberies in the Terra di Lavoro, but by good luck combined with
audacity he always escaped capture, whence his name of Fra Diavolo,
popular superstition having invested him with the characters of a monk
and a demon, and it seems that at one time he actually was a monk. When
the kingdom of Naples was overrun by the French and the Parthenopaean
Republic established (1799), Cardinal Ruffo, acting on behalf of the
Bourbon king Ferdinand IV., who had fled to Sicily, undertook the
reconquest of the country, and for this purpose he raised bands of
peasants, gaol-birds, brigands, &c., under the name of Sanfedisti or
_bande della Santa Fede_ ("bands of the Holy Faith"). Fra Diavolo was
made leader of one of them, and waged untiring war against the French
troops, cutting off isolated detachments and murdering stragglers and
couriers. Owing to his unrivalled knowledge of the country, he succeeded
in interrupting the enemy's communications between Rome and Naples. But
although, like his fellow-brigands under Ruffo, he styled himself "the
faithful servant and subject of His Sicilian Majesty," wore a military
uniform and held military rank, and was even created duke of Cassano,
his atrocities were worthy of a bandit chief. On one occasion he threw
some of his prisoners, men, women and children, over a precipice, and
on another he had a party of seventy shot. His excesses while at Albano
were such that the Neapolitan general Naselli had him arrested and
imprisoned in the castle of St Angelo, but he was liberated soon after.
When Joseph Bonaparte was made king of Naples, extraordinary tribunals
were established to suppress brigandage, and a price was put on Fra
Diavolo's head. After spreading terror through Calabria, he crossed over
to Sicily, where he concerted further attacks on the French. He returned
to the mainland at the head of 200 convicts, and committed further
excesses in the Terra di Lavoro; but the French troops were everywhere
on the alert to capture him and he had to take refuge in the woods of
Lenola. For two months he evaded his pursuers, but at length, hungry and
ill, he went in disguise to the village of Baronissi, where he was
recognized and arrested, tried by an extraordinary tribunal, condemned
to death and shot. In his last moments he cursed both the Bourbons and
Admiral Sir Sidney Smith for having induced him to engage in this
reckless adventure (1806). Although his cruelty was abominable, he was
not altogether without generosity, and by his courage and audacity he
acquired a certain romantic popularity. His name has gained a world-wide
celebrity as the title of a famous opera by Auber.

  The best known account of Fra Diavolo is in Pietro Colletta's _Storia
  del reame di Napoli_ (2nd ed., Florence, 1848); B. Amante's _Fra
  Diavolo e il suo tempo_ (Florence, 1904) is an attempted
  rehabilitation; but A. Luzio, whose account in _Profili e bozzetti
  storici_ (Milan, 1906) gives the latest information on the subject,
  has demolished Amante's arguments.     (L. V.*)




DIAZ, NARCISSE VIRGILIO (1808-1876), French painter, was born in
Bordeaux of Spanish parents, on the 25th of August 1808. At first a
figure-painter who indulged in strong colour, in his later life Diaz
became a painter of the forest and a "tone artist" of the first order.
He spent much time at Barbizon; and although he is the least exalted of
the half-dozen great artists who are usually grouped round that name, he
sometimes produced works of the highest quality. At the age of ten Diaz
became an orphan, and misfortune dogged his earlier years. His foot was
bitten by a reptile in Meudon wood, near Sèvres, where he had been taken
to live with some friends of his mother. The bite was badly dressed, and
ultimately it cost him his leg. Afterwards his wooden stump became
famous. At fifteen he entered the studios at Sèvres, where the
decoration of porcelain occupied him; but tiring of the restraint of
fixed hours, he took to painting Eastern figures dressed in richly
coloured garments. Turks and Oriental scenes attracted him, and many
brilliant gems remain of this period. About 1831 Diaz encountered
Théodore Rousseau, for whom he entertained a great veneration, although
Rousseau was four years his junior; but it was not until ten years later
that the remarkable incident took place of Rousseau teaching Diaz to
paint trees. At Fontainebleau Diaz found Rousseau painting his wonderful
forest pictures, and determined to paint in the same way if possible.
Rousseau, then in poor health, worried at home, and embittered against
the world, was difficult to approach. Diaz followed him surreptitiously
to the forest,--wooden leg not hindering,--and he dodged round after the
painter, trying to observe his method of work. After a time Diaz found a
way to become friendly with Rousseau, and revealed his anxiety to
understand his painting. Rousseau was touched with the passionate words
of admiration, and finally taught Diaz all he knew. Diaz exhibited many
pictures at the Paris Salon, and was decorated in 1851. During the
Franco-German War he went to Brussels. After 1871 he became fashionable,
his works gradually rose in the estimation of collectors, and he worked
constantly and successfully. In 1876 he caught cold at his son's grave,
and on the 18th of November of that year he died at Mentone, whither he
had gone to recruit his health. Diaz's finest pictures are his forest
scenes and storms, and it is on these, and not on his pretty figures,
that his fame is likely to rest. There are several fairly good examples
of the master in the Louvre, and three small figure pictures in the
Wallace collection, Hertford House. Perhaps the most notable of Diaz's
works are "La Fée aux Perles" (1857), in the Louvre; "Sunset in the
Forest" (1868); "The Storm," and "The Forest of Fontainebleau" (1870)
at Leeds. Diaz had no well-known pupils, but Léon Richet followed
markedly his methods of tree-painting, and J. F. Millet at one period
painted small figures in avowed imitation of Diaz's then popular
subjects.

  See A. Hustin, _Les Artistes célèbres: Diaz_ (Paris); D. Croal
  Thomson, _The Barbizon School of Painters_ (London, 1890); J. W.
  Mollett, _Diaz_ (London, 1890); J. Claretie, _Peintres et sculpteurs
  contemporains: Diaz_ (Paris, 1882); Albert Wolff, _La Capitale de
  l'art: Narcisse Diaz_ (Paris, 1886); Ph. Burty, _Maîtres et
  petit-maîtres: N. Diaz_ (Paris, 1877). (D.C.T.)




DIAZ, PORFIRIO (1830-   ), president of the republic of Mexico (q.v.),
was born in the southern state of Oaxaca, on the 15th of September 1830.
His father was an innkeeper in the little capital of that province, and
died three years after the birth of Porfirio, leaving a family of seven
children. The boy, who had Indian blood in his veins, was educated for
the Catholic Church, a body having immense influence in the country at
that time and ordering and controlling revolutions by the strength of
their filled coffers. Arrived at the age of sixteen Porfirio Diaz threw
off the authority of the priests. Fired with enthusiasm by stories told
by the revolutionary soldiers continually passing through Oaxaca, and
hearing about the war with the United States, a year later he determined
to set out for Mexico city and join the National Guard. There being no
trains, and he being too poor to ride, he walked the greater part of the
250 m., but arrived there too late, as the treaty of Guadalupe-Hidalgo
(1848) had been already signed, and Texas finally ceded to the United
States. Thus his entering the army was for the time defeated. Thereupon
he returned to his native town and began studying law. He took pupils in
order to pay his own fees at the Law Institute, and help his mother. At
this time he came under the notice and influence of Don Marcos Pérez and
Benito Juárez, the first a judge, the second a governor of the state of
Oaxaca, and soon to become famous as the deliverer of Mexico from the
priesthood (War of Reform). Diaz continued in his native town until
1854, when, refusing to vote for the dictator, Santa Anna, he was stung
by a taunt of cowardice, and hastily pushing his way to the voting
place, he recorded his vote in favour of Alvarez and the revolutionists.
Orders were given for his arrest, but seizing a rifle and mounting a
horse he placed himself at the head of a few revolting peasants, and
from that moment became one of the leading spirits in that long struggle
for reform, known as the War of Reform, which, under the leadership of
Juárez, followed the overthrow of Santa Anna. Promotion succeeded
promotion, as Diaz led his troops from victory to victory, amid great
privations and difficulties. He was made captain (1856),
lieutenant-colonel and colonel (1859), brigadier-general (1861), and
general of division for the army (1863). Closely following on civil war,
political strife, open rebellion and the great War of Reform, came the
French invasion of 1862, and the landing of the emperor Maximilian in
1864. From the moment the French disclosed their intentions of settling
in Mexico in 1862, Diaz took a prominent part against the foreign
invasion. He was twice seriously wounded, imprisoned on three different
occasions, had two hairbreadth escapes, and took part in many daring
engagements. So important a personage did he become that both Marshal
Bazaine and the emperor Maximilian made overtures to him. At the time of
Maximilian's death (with which Diaz personally had nothing to do) he was
carrying on the siege of Mexico city, which ended in the surrender of
the town two days after the emperor was shot at Quérétaro between his
two leading generals. Diaz at once set to work to pay up arrears due to
his soldiers, proclaimed death as the penalty of plunder and theft, and
in the few weeks that followed showed his great administrative powers,
the officers as well as the rank and file receiving arrears of pay. On
the very day that he occupied Mexico city, the great commander of the
army of the east, to everyone's surprise, sent in his resignation. He
was, indeed, appointed to the command of the second division of the army
by President Juárez in his military reorganization, but Diaz, seeing men
who had given great and loyal service to the state dismissed from their
positions in the government, and disgusted at this course, retired to
the little city of Oaxaca; there he lived, helping in the
reorganization of the army but taking no active part in the government
until 1871.

On Juárez' death Lerdo succeeded as president, in 1872. His term of
office again brought discord, and when it was known that he was
attempting to be re-elected in 1876, the storm broke. Diaz came from
retirement, took up the leadership against Lerdo, and after desperate
struggles and a daring escape finally made a triumphal entry into Mexico
city on the 24th of November 1876, as provisional president, quickly
followed by the full presidentship. His term of office marks a prominent
change in the history of Mexico; from that date he at once forged ahead
with financial and political reform, the scrupulous settlement of all
national debts, the welding together of the peoples and tribes (there
are 150 different Indian tribes) of his country, the establishment of
railroads and telegraphs, and all this in a land which had been upheaved
for a century with revolutions and bloodshed, and which had had
fifty-two dictators, presidents and rulers in fifty-nine years. In 1880
Diaz was succeeded by Gonzalez, the former minister of war, for four
years (owing to the limit of the presidential office), but in 1884 he
was unanimously re-elected. The government having set aside the
above-mentioned limitation, Diaz was continually re-elected to the
presidency. He married twice and had a son and two daughters. His gifted
second wife (Carmelita), very popular in Mexico, was many years younger
than himself. King Edward VII. made him an honorary grand commander of
the Bath in June 1906, in recognition of his wonderful administration as
perpetual president for over a quarter of a century.

  See also Mrs Alec Tweedie, _Porfirio Diaz, Seven Times President of
  Mexico_ (1906), and _Mexico as I saw it_ (1901); Dr Noll, _From Empire
  to Republic_ (1890); Lieut. Seaton Schroeder, _Fall of Maximilian's
  Empire_ (New York, 1887); R. de Z. Enriquez, _P. Diaz_ (1908); and an
  article by Percy Martin in _Quarterly Review_ for October 1909.
       (E. A. T.)




DIAZ DE NOVAES, BARTHOLOMEU (fl. 1481-1500), Portuguese explorer,
discoverer of the Cape of Good Hope, was probably a kinsman of João
Diaz, one of the first Portuguese to round Cape Bojador (1434), and of
Diniz Diaz, the discoverer of Cape Verde (1445). In 1478 a Bartholomeu
Diaz, probably identical with the discoverer, was exempted from certain
customary payments on ivory brought from the Guinea coast. In 1481 he
commanded one of the vessels sent by King John II. under Diogo
d'Azambuja to the Gold Coast. In 1486 he seems to have been a cavalier
of the king's household, and superintendent of the royal warehouses; on
the 10th of October in this year he received an annuity of 6000 reis
from King John for "services to come"; and some time after this
(probably about July or August 1487, rather than July 1486, the
traditional date) he left Lisbon with three ships to carry on the work
of African exploration so greatly advanced by Diogo Cão (1482-1486).
Passing Cão's farthest point near Cape Cross (in the modern German
South-west Africa and) in 21° 50´ S., he erected a pillar on what is now
known as Diaz Point, south of Angra Pequena or Lüderitz Bay, in 26° 38´
S.; of this fragments still exist. From this point (according to De
Barros) Diaz ran thirteen days southwards before strong winds, which
freshened to dangerous stormy weather, in a comparatively high southern
latitude, considerably south of the Cape. When the storm subsided the
Portuguese stood east; and failing, after several days' search, to find
land, turned north, and so struck the south coast of Cape Colony at
Mossel Bay (Diaz' Bahia dos Vaqueiros), half way between the Cape of
Good Hope and Port Elizabeth (February 3, 1488). Thence they coasted
eastward, passing Algoa Bay (Diaz' Bahia da Roca), erecting pillars (or
perhaps wooden crosses), it is said, on one of the islands in this bay
and at or near Cape Padrone farther east; of these no traces remain. The
officers and men now began to insist on return, and Diaz could only
persuade them to go as far as the estuary of the Great Fish River (Diaz'
Rio do Iffante, so named from his colleague, Captain João Iffante).
Here, however, half way between Port Elizabeth and East London (and
indeed from Cape Padrone), the north-easterly trend of the coast became
unmistakable; the way round Africa had been laid open. On his return
Diaz perhaps named Cape Agulhas after St Brandan; while on the
southernmost projection of the modern Cape peninsula, whose remarkable
highlands (Table Mountain, &c.) doubtless impressed him as the practical
termination of the continent, he bestowed, says De Barros, the name of
Cape of Storms (_Cabo Tormentoso_) in memory of the storms he had
experienced in these far southern waters; this name (in the ordinary
tradition) was changed by King John to that of Good Hope (_Cabo da Boa
Esperança_). Some excellent authorities, however, make Diaz himself give
the Cape its present name. Hard by this "so many ages unknown
promontory" the explorer probably erected his last pillar. After
touching at the Ilha do Principe (Prince's Island, south-west of the
Cameroons) as well as at the Gold Coast, he appeared at Lisbon in
December 1488. He had discovered 1260 m. of hitherto unknown coast; and
his voyage, taken with the letters soon afterwards received from Pero de
Covilhão (who by way of Cairo and Aden had reached Malabar on one side
and the "Zanzibar coast" on the other as far south as Sofala, in
1487-1488) was rightly considered to have solved the question of an
ocean route round Africa to the Indies and other lands of South and East
Asia.

No record has yet been found of any adequate reward for Diaz: on the
contrary, when the great Indian expedition was being prepared (for Vasco
da Gama's future leadership) Bartolomeu only superintended the building
and outfit of the ships; when the fleet sailed in 1497, he only
accompanied da Gama to the Cape Verde Islands, and after this was
ordered to El Mina on the Gold Coast. On Cabral's voyage of 1500 he was
indeed permitted to take part in the discovery of Brazil (April 22), and
thence should have helped to guide the fleet to India; but he perished
in a great storm off his own Cabo Tormentoso. Like Moses, as Galvano
says, he was allowed to see the Promised Land, but not to enter in.

  See João de Barros, _Asia_, Dec. I. bk. iii. ch. 4; Duarte Pacheco
  Pereira, _Esmeraldo de situ orbis_, esp. pp. 15, 90, 92, 94 and
  Raphael Bastos's introduction to the edition of 1892 (Pacheco met
  Diaz, returning from his great voyage, at the Ilha do Principe); a
  marginal note, probably by Christopher Columbus himself, on fol. 13 of
  a copy of Pierre d'Ailly's _Imago mundi_, now in the Colombina at
  Seville (the writer of this note fixes Diaz's return to Lisbon,
  December 1488, and says he was present at Diaz's interview with the
  king of Portugal, when the explorer described his voyage and showed
  his route upon the chart he had kept); a similar but briefer note in a
  copy of Pope Pius II.'s _Historia rerum ubique gestarum_, from the
  same hand; the _Roteiro_ of Vasco da Gama's First Voyage (_Journal of
  the First Voyage of ... Da Gama_, Hakluyt Soc., ed. E. G. Ravenstein
  (1898), pp. 9, 14); Ramusio, _Navigationi_ (3rd ed.), vol. i. fol.
  144; Castanheda, _Historia_, bk. i. ch. 1; Galvano, _Descobrimentos
  (Discoveries of the World)_, Hakluyt Soc. (1862), p. 77; E. G.
  Ravenstein, "Voyages of ... Cão and ... Dias," in _Geog. Journ._
  (London, December 1900), vol. xvi. pp. 638-655), an excellent critical
  summary in the light of the most recent investigations of all the
  material. The fragments of Diaz's only remaining pillar (from Diaz
  Point) are now partly at the Cape Museum, partly at Lisbon: the latter
  are photographed in Ravenstein's paper in _Geog. Journ._ (December
  1900, p. 642).     (C. R. B.)




DIAZO COMPOUNDS, in organic chemistry, compounds of the type R·N·2·X
(where R = a hydrocarbon radical, and X = an acid radical or a hydroxyl
group). These compounds may be divided into two classes, namely, the
true diazo compounds, characterized by the grouping - N = N -, and the
diazonium compounds, characterized by the grouping N:·N<.

The diazonium compounds were first discovered by P. Griess (_Ann._,
1858, 106, pp. 123 et seq.), and may be prepared by the action of
nitrous fumes on a well-cooled solution of a salt of a primary amine,

  C6H5NH2·HNO3 + HNO2 = C6H5N2·NO3 + 2H2O,

or, as is more usually the case (since the diazonium salts themselves
are generally used only in aqueous solution) by the addition of a
well-cooled solution of potassium or sodium nitrite to a well-cooled
dilute acid solution of the primary amine. In order to isolate the
anhydrous diazonium salts, the method of E. Knoevenagel (_Ber._, 1890,
23, p. 2094) may be employed. In this process the amine salt is
dissolved in absolute alcohol and diazotized by the addition of amyl
nitrite; a crystalline precipitate of the diazonium salt is formed on
standing, or on the addition of a small quantity of ether. The diazonium
salts are also formed by the action of zinc-dust and acids on the
nitrates of primary amines (R. Mohlau, _Ber._, 1883, 16, p. 3080), and
by the action of hydroxylamine on nitrosobenzenes. They are colourless
crystalline solids which turn brown on exposure. They dissolve easily in
water, but only to a slight extent in alcohol and ether. They are very
unstable, exploding violently when heated or rubbed. _Benzene diazonium
nitrate_, C6H5N(NO3):·N, crystallizes in long silky needles. The
sulphate and chloride are similar, but they are not quite so unstable as
the nitrate. The bromide may be prepared by the addition of bromine to
an ethereal solution of diazo-amino-benzene (tribromaniline remaining in
solution). By the addition of potassium bromide and bromine water to
diazonium salts they are converted into a _perbromide_, e.g. C6H5N2Br3,
which crystallizes in yellow plates.

  The diazonium salts are characterized by their great reactivity and
  consequently are important reagents in synthetical processes, since by
  their agency the amino group in a primary amine may be exchanged for
  other elements or radicals. The chief reactions are as follows:--

  1. _Replacement of -NH2 by -OH_:--The amine is diazotized and the
  aqueous solution of the diazonium salt is heated, nitrogen being
  eliminated and a phenol formed.

  2. _Replacement of -NH2 by halogens and by the -CN and -CNO
  groups_:--The diazonium salt is warmed with an acid solution of the
  corresponding cuprous salt (T. Sandmeyer, _Ber._, 1884, 17, p. 2650),
  or with copper powder (L. Gattermann, Ber., 1890, 23, p. 1218; 1892,
  25, p. 1074). In the case of iodine, the substitution is effected by
  adding a warm solution of potassium iodide to the diazonium solution,
  no copper or cuprous salt being necessary; whilst for the production
  of nitriles a solution of potassium cuprous cyanide is used. This
  reaction (the so-called "Sandmeyer" reaction) has been investigated by
  A. Hantzsch and J. W. Blagden (_Ber._, 1900, 33, p. 2544), who
  consider that three simultaneous reactions occur, namely, the
  formation of labile double salts which decompose in such a fashion
  that the radical attached to the copper atom wanders to the aromatic
  nucleus; a catalytic action, in which nitrogen is eliminated and the
  acid radical attaches itself to the aromatic nucleus; and finally, the
  formation of azo compounds.

  3. _Replacement of -NH2 by -NO2_:--A well-cooled concentrated solution
  of potassium mercuric nitrate is added to a cooled solution of benzene
  diazonium nitrate, when the crystalline salt 2C6H5N2·NO3, Hg(NO2)2 is
  precipitated. On warming this with copper powder, it gives a
  quantitative yield of nitrobenzene (A. Hantzsch, _Ber._, 1900, 33, p.
  2551).

  4. _Replacement of -NH2 by hydrogen_:--This exchange is brought about,
  in some cases, by boiling the diazonium salt with alcohol; but I.
  Remsen and his pupils (_Amer. Chem. Journ._, 1888, 9, pp. 389 et seq.)
  have shown that the main product of this reaction is usually a
  phenolic ether. This reaction has also been investigated by A.
  Hantzsch and E. Jochem (_Ber._, 1901, 34, p. 3337), who arrived at the
  conclusion that the normal decomposition of diazonium salts by
  alcohols results in the formation of phenolic ethers, but that an
  increase in the molecular weight of the alcohol, or the accumulation
  of negative groups in the aromatic nucleus, diminishes the yield of
  the ether and increases the amount of the hydrocarbon formed. The
  replacement is more readily brought about by the use of sodium
  stannite (P. Friedlander, _Ber._, 1889, 22, p. 587), or by the use of
  a concentrated solution of hypophosphorous acid (J. Mai, _Ber._, 1902,
  35, p. 162). A. Hantzsch (_Ber._, 1896, 29, p. 947; 1898, 31, p. 1253)
  has shown that the chlor- and brom- diazoniumthiocyanates, when
  dissolved in alcohol containing a trace of hydrochloric acid, become
  converted into the isomeric thiocyanbenzene diazonium chlorides and
  bromides. This change only occurs when the halogen atom is in the
  ortho- or para- position to the -N2- group.

  _Metallic Diazo Derivatives._--Benzene diazonium chloride is
  decomposed by silver oxide in aqueous solution, with the formation of
  _benzene diazonium hydroxide_, C6H5·N(OH):·N. This hydroxide, although
  possessing powerful basic properties, is unstable in the presence of
  alkalis and neutralizes them, being converted first into the isomeric
  benzene-diazotic acid, the potassium salt of which is obtained when
  the diazonium chloride is added to an excess of cold concentrated
  potash (A. Hantzsch and W. B. Davidson, _Ber._, 1898, 31, p. 1612).
  _Potassium benzene diazotate_, C6H5N2·OK, crystallizes in colourless
  silky needles. The free acid is not known; by the addition of the
  potassium salt to 50% acetic acid at -20° C., the acid anhydride,
  _benzene diazo oxide_, (C6H5N2)2O, is obtained as a very unstable,
  yellow, insoluble compound, exploding spontaneously at 0° C. Strong
  acids convert it into a diazonium salt, and potash converts it into
  the diazotate. On the constitution, of these anhydrides see E.
  Bamberger, _Ber._, 1896, 29, p. 446, and A. Hantzsch, _Ber._, 1896,
  29, p. 1067; 1898, 31, p. 636. By the addition of the diazonium salts
  to a hot concentrated solution of a caustic alkali, C. Schraube and C.
  Schmidt (_Ber._, 1894, 27, p. 520) obtained an isomer of potassium
  benzene diazotate. These _iso-_diazotates are formed much more readily
  when the aromatic nucleus in the diazonium salt contains negative
  radicals. _Potassium benzene iso-diazotate_ resembles the normal salt,
  but is more stable, and is more highly ionized. Carbon dioxide
  converts it into _phenyl nitrosamine_, C6H5NH·NO (A. Hantzsch). The
  potassium salt of the iso-diazo hydroxide yields on methylation a
  nitrogen ether, R·N(CH3)·NO, whilst the silver salt yields an oxygen
  ether, R·N:N·OCH3. These results point to the conclusion that the
  iso-diazo hydroxide is a tautomeric substance. The same oxygen ether
  is formed by the methylation of the silver salt of the normal diazo
  hydroxide; this points to the conclusion that the isomeric hydroxides,
  corresponding with the silver derivatives, have the same structural
  formulae, namely, R·N:N·OH. These oxygen ethers contain the grouping
  -N:N-, since they couple very readily with the phenols in alkaline
  solution to form azo compounds (q.v.) (E. Bamberger, _Ber._, 1895, 28,
  p. 225); they are also explosive.

  By oxidizing potassium benzene iso-diazotate with alkaline potassium
  ferricyanide, E. Bamberger (_Ber._, 1894, 27, p. 914) obtained the
  _diazoic acids_, R·NH·NO2, substances which he had previously prepared
  by similarly oxidizing the diazonium salts, by dehydrating the
  nitrates of primary amines with acetic anhydride, and by the action of
  nitric anhydride on the primary amines. Concentrated acids convert
  them into the isomeric nitro-amines, the -NO2 group going into the
  nucleus in the ortho- or para- position to the amine nitrogen; this
  appears to indicate that the compounds are nitramines. They behave,
  however, as tautomeric substances, since their alkali salts on
  methylation give nitrogen ethers, whilst their silver salts yield
  oxygen ethers:

            /-->  potassium salt --> R·N(CH3)·NO2 nitramine.
  R·NH·NO2<
            \-->  silver salt    --> R·N:N·O·OCH3 diazoate.

  _Phenyl nitramine_, C6H5NH·NO2, is a colourless crystalline solid,
  which melts at 46° C. Sodium amalgam in alkaline solution reduces it
  to phenylhydrazine.

  _Constitution of the Diazo Compounds._--P. Griess (_Ann._, 1866, 137,
  p. 39) considered that the diazo compounds were formed by the addition
  of complex groupings of the type C6H4N2- to the inorganic acids;
  whilst A. Kekulé (_Zeit. f. Chemie_, 1866, 2, p. 308), on account of
  their ready condensation to form azo compounds and their easy
  reduction to hydrazines, assumed that they were substances of the type
  R·N:N·Cl. The constitution of the diazonium group -N2·X, may be
  inferred from the following facts:--The group C6H5N2- behaves in many
  respects similarly to an alkali metal, and even more so to the
  ammonium group, since it is capable of forming colourless neutral
  salts with mineral acids, which in dilute aqueous solution are
  strongly ionized, but do not show any trace of hydrolytic dissociation
  (A. Hantzsch, _Ber._, 1895, 28, p. 1734). Again, the diazonium
  chlorides combine with platinic chloride to form difficultly soluble
  double platinum salts, such as (C6H5N2Cl)2·PtCl4; similar gold salts,
  C6H5N2Cl·AuCl3, are known. Determinations of the electrical
  conductivity of the diazonium chloride and nitrate also show that the
  diazonium radical is strictly comparable with other quaternary
  ammonium ions. For these reasons, one must assume the existence of
  pentavalent nitrogen in the diazonium salts, in order to account for
  their basic properties.

  The constitution of the isomeric diazo hydroxides has given rise to
  much discussion. E. Bamberger (_Ber._, 1895, 28, pp. 444 et seq.) and
  C. W. Blomstrand (_Journ. prakt. Chem._, 1896, 53, pp. 169 et seq.)
  hold that the compounds are structurally different, the normal
  diazo-hydroxide being a diazonium derivative of the type
  R·N([3:]N)·OH. The recent work of A. Hantzsch and his pupils seems to
  invalidate this view (_Ber._, 1894, 27, pp. 1702 et seq.; see also A.
  Hantzsch, _Die Diazoverbindungen_). According to Hantzsch the isomeric
  diazo hydroxides are structurally identical, and the differences in
  behaviour are due to stereo-chemical relations, the isomerism being
  comparable with that of the oximes (q.v.). On such a hypothesis, the
  relatively unstable normal diazo hydroxides would be the
  _syn-_compounds, since here the nitrogen atoms would be more easily
  eliminated, whilst the stable iso-diazo derivatives would be the
  _anti-_compounds, thus:

         R · N             R · N
             ..                ..
        HO · N                 N · OH
    Normal hydroxide      Iso hydroxide
    (Syn-compound)       (Anti-compound)

  In support of this theory, Hantzsch has succeeded in isolating a
  series of syn- and anti-diazo-cyanides and -sulphonates (_Ber._, 1895,
  28, p. 666; 1900, 33, p. 2161; 1901, 34, p. 4166). By diazotizing
  para-chloraniline and adding a cold solution of potassium cyanide, a
  salt (melting at 29° C.) is obtained, which readily loses nitrogen,
  and forms para-chlorbenzonitrile on the addition of copper powder. By
  dissolving this diazocyanide in alcohol and reprecipitating it by
  water, it is converted into the isomeric diazocyanide (melting at
  105-106° C.), which does not yield para-chlorbenzonitrile when treated
  with copper powder. Similar results have been obtained by using
  diazotized para-anisidine, a syn- and an anti- compound being formed,
  as well as a third isomeric cyanide, obtained by evaporating
  para-methoxy-benzenediazonium hydroxide in the presence of an excess
  of hydrocyanic acid at ordinary temperatures. This salt is a
  colourless crystalline substance of composition
  CH3O·C6H4·N2·CN·HCN·2H2O, and has the properties of a metallic salt;
  it is very soluble in water and its solution is an electrolyte,
  whereas the solutions of the syn-and anti- compounds are not
  electrolytes. The isolation of these compounds is a powerful argument
  in favour of the Hantzsch hypothesis which requires the existence of
  these three different types, whilst the Bamberger-Blomstrand view only
  accounts for the formation of two isomeric cyanides, namely, one of
  the normal diazonium type and one of the iso-diazocyanide type.

  Benzene diazonium hydroxide, although a strong base, reacts with the
  alkaline hydroxides to form salts with the evolution of heat, and
  generally behaves as a weak acid. On mixing dilute solutions of the
  diazonium hydroxide and the alkali together, it is found that the
  molecular conductivity of the mixture is much less than the sum of the
  two electrical conductivities of the solutions separately, from which
  it follows that a portion of the ions present have changed to the
  non-ionized condition. This behaviour is explained by considering the
  non-ionized part of the diazonium hydroxide to exist in solution in a
  hydrated form, the equation of equilibrium being:

          C6H5·N·       --> C6H5·N·OH
    H2O +     ... + OH'          |
               N        <--   HO·N·H

  On adding the alkaline hydroxide to the solution, this hydrate is
  supposed to lose water, yielding the syn-diazo hydroxide, which then
  gives rise to a certain amount of the sodium salt (A. Hantzsch,
  _Ber._, 1898, 31, p. 1612),

           ....
    C6H5·N·:OH:  -->  C6H5·N  -->  C6H5·N
         | :  :            ||           ||
      HO·N·:H :  <--    HO·N  <--   NaO·N
           ....

  This assumption also shows the relationship of the diazonium
  hydroxides to other quaternary ammonium compounds, for most of the
  quaternary ammonium hydroxides (except such as have the nitrogen atom
  attached to four saturated hydrocarbon radicals) are unstable, and
  readily pass over into compounds in which the hydroxyl group is no
  longer attached to the amine nitrogen; thus the syn-diazo hydroxides
  are to be regarded as pseudo-diazonium derivatives. (A. Hantzsch,
  _Ber._, 1899, 32, p. 3109; 1900, 33, p. 278.) It is generally accepted
  that the iso-diazo hydroxides possess the oxime structure R·N:N·OH.

  Hantzsch explains the characteristic reactions of the diazonium
  compounds by the assumption that an addition compound is first formed,
  which breaks down with the elimination of the hydride of the acid
  radical, and the formation of an unstable syn-diazo compound, which,
  in its turn, decomposes with evolution of nitrogen (_Ber._, 1897, 30,
  p. 2548; 1898, 31, p. 2053).

     R         X     R      X     R   X
      \        |      \    /      |   |
        N·:N + | -->   N·:N   --> |   | + HCl --> R·X + N2.
      /        |      /    \      |   |
    Cl         H    Cl      H     N = N

  J. Cain (_Jour. Chem. Soc._, 1907, 91, p. 1049) suggested a quinonoid
  formula for diazonium salts, which has been combated by Hantzsch
  (_Ber._, 1908, 41, pp. 3532 et seq.). G. T. Morgan and F. M. G.
  Micklethwaite (_Jour. Chem. Soc._, 1908, 93, p. 617; 1909, 95, p.
  1319) have pointed out that the salts may possess a dynamic formula,
  Cain's representing the middle stage, thus:

        /||\                /||\                /||\
       / || \              / || \              / || \
    H / N·Cl \ H        H / N·Cl \ H        H / N·Cl \ H
     |\  ||  ||  --->    ||  ||   |  --->    ||  ||  /|
     | \ ||  ||  <---    ||  ||   |  <---    ||  || / |
     |  \N   ||          ||  N    |          ||   N   |
    H\\      / H        H\\  |   / H        H \      //H
      \\    /             \\ |  /              \    //
       \\  /               \\| /                \  //
         H                   H                   H

  _Diazoamines._--The diazoamines, R·N2·NHR, may be prepared by the
  action of the primary and secondary amines on the diazonium salts, or
  by the action of nitrous acid on the free primary amine. In the latter
  reaction it is assumed that the isodiazohydroxide first formed is
  immediately attacked by a second molecule of the amine. They are
  yellow crystalline solids, which do not unite with acids. Nitrous acid
  converts them, in acid solution, into diazonium salts.

    C6H5N2·NHC6H5 + 2HCl + HNO2 = 2C6H5N2Cl + 2H2O.

  They are readily converted into the isomeric aminoazo compounds,
  either by standing in alcoholic solution, or by warming with a mixture
  of the parent base and its hydrochloride; the diazo group preferably
  going into the para-position to the amino group. When the
  para-position is occupied, the diazo group takes the ortho-position.
  H. Goldschmidt and R. U. Reinders (_Ber._, 1896, 29, p. 1369, 1899)
  have shown that the transformation is a monomolecular reaction, the
  velocity of transformation in moderately dilute solution being
  independent of the concentration, but proportional to the amount of
  the catalyst present (amine hydrochloride) and to the temperature. It
  has also been shown that when different salts of the amine are used,
  their catalytic influence varies in amount and is almost proportional
  to their degree of ionization in aqueous solution. Diazoaminobenzene,
  C6H5N2·NHC6H5, crystallizes in golden yellow laminae, which melt at
  96° C. and explode at a slightly higher temperature. It is readily
  soluble in alcohol, ether and benzene. Concentrated hydrochloric acid
  converts it into chlorbenzene, aniline and nitrogen. Zinc dust and
  alcoholic acetic acid reduce it to aniline and phenylhydrazine.

  _Diazoimino compounds_, R·N3, may be regarded as derivatives of
  azoimide (q.v.); they are formed by the action of ammonia on the
  diazoperbromides, or by the action of hydroxylamine on the diazonium
  sulphates (J. Mai, _Ber._, 1892, 25, p. 372; T. Curtius, _Ber._, 1893,
  26, p. 1271). Diazobenzeneimide, C6H5N3, is a yellowish oil of
  stupefying odour. It boils at 59° C. (12 mm.), and explodes when
  heated. Concentrated hydrochloric acid decomposes it with formation of
  chloranilines and elimination of nitrogen, whilst on boiling with
  sulphuric acid it is converted into aminophenols.

  _Aliphatic Diazo Compounds._--The esters of the aliphatic amino acids
  may be diazotized in a manner similar to the primary aromatic amines,
  a fact discovered by T. Curtius (_Ber._, 1833, 16, p. 2230). The first
  aliphatic diazo compound to be isolated was _diazoacetic ester_,
  CH·N2·CO2C2H5, which is prepared by the action of potassium nitrite on
  the ethyl ester of glycocoll hydrochloride, HCl·NH2·CH2·CO2C2H5 + KNO2
  = CHN2·CO2C2H5 + KCl + 2H2O. It is a yellowish oil which melts at -24°
  C.; it boils at 143-144° C., but cannot be distilled safely as it
  decomposes violently, giving nitrogen and ethyl fumarate. It explodes
  in contact with concentrated sulphuric acid. On reduction it yields
  ammonia and glycocoll (aminoacetic acid). When heated with water it
  forms ethyl hydroxy-acetate; with alcohol it yields ethyl
  ethoxyacetate. Halogen acids convert it into monohalogen fatty acids,
  and the halogens themselves convert it into dihalogen fatty acids. It
  unites with aldehydes to form esters of ketonic acids, and with
  aniline yields anilido-acetic acid. It forms an addition product with
  acrylic ester, which on heating loses nitrogen and leaves trimethylene
  dicarboxylic ester. Concentrated ammonia converts it into
  _diazoacetamide_, CHN2·CONH2, which crystallizes in golden yellow
  plates which melt at 114° C. For other reactions see HYDRAZINE. The
  constitution of the diazo fatty esters is inferred from the fact that
  the two nitrogen atoms, when split off, are replaced by two monovalent
  elements or groups, thus leading to the formula

     N \
    ..  > CH·CO2C2H5, for diazoacetic ester.
     N /

  _Diazosuccinic ester_, N2·C(CO2C2H5)2, is similarly prepared by the
  action of nitrous acid on the hydrochloride of aspartic ester. It is
  decomposed by boiling water and yields fumaric ester.

  _Diazomethane_, CH2N2, was first obtained in 1894 by H. v. Pechmann
  (_Ber._, 1894, 27, p. 1888; 1895, 28, p. 855). It is prepared by the
  action of aqueous or alcoholic solutions of the caustic alkalis on the
  nitroso-acidyl derivatives of methylamine (such, for example, as
  _nitrosomethyl urethane_, NO·N(CH3)·CO2C2H5, which is formed on
  passing nitrous fumes into an ethereal solution of methyl urethane).
  E. Bamberger (_Ber._, 1895, 28, p. 1682) regards it as the anhydride
  of iso-diazomethane, CH3·N:N·OH, and has prepared it by a method
  similar to that used for the preparation of iso-diazobenzene. By the
  action of bleaching powder on methylamine hydrochloride, there is
  obtained a volatile liquid (_methyldichloramine_, CH3·N·Cl2), boiling
  at 58-60° C., which explodes violently when heated with water,
  yielding hydrocyanic acid (CH3NCl2 = HCN + 2HCl). Well-dried
  hydroxylamine hydrochloride is dissolved in methyl alcohol and mixed
  with sodium methylate; a solution of methyldichloramine in absolute
  ether is then added and an ethereal solution of diazomethane distils
  over. Diazomethane is a yellow inodorous gas, very poisonous and
  corrosive. It may be condensed to a liquid, which boils at about 0° C.
  It is a powerful methylating agent, reacting with water to form methyl
  alcohol, and converting acetic acid into methylacetate, hydrochloric
  acid into methyl chloride, hydrocyanic acid into acetonitrile, and
  phenol into anisol, nitrogen being eliminated in each case. It is
  reduced by sodium amalgam (in alcoholic solution) to
  _methylhydrazine_, CH3·NH·NH2. It unites directly with acetylene to
  form pyrazole (H. v. Pechmann, _Ber._, 1898, 31, p. 2950) and with
  fumaric methyl ester it forms pyrazolin dicarboxylic ester.
       (F. G. P.*)

    See G. T. Morgan, _B.A. Rep._, 1902; J. Cain, _Diazo Compounds_,
    1908.




DIAZOMATA (Gr. [Greek: diazôma], a girdle), in architecture, the landing
places and passages which were carried round the semicircle and
separated the upper and lower tiers in a Greek theatre.




DIBDIN, CHARLES (1745-1814), British musician, dramatist, novelist,
actor and song-writer, the son of a parish clerk, was born at
Southampton on or before the 4th of March 1745, and was the youngest of
a family of eighteen. His parents designing him for the church, he was
sent to Winchester; but his love of music early diverted his thoughts
from the clerical profession. After receiving some instruction from the
organist of Winchester cathedral, where he was a chorister from 1756 to
1759, he went to London at the age of fifteen. Here he was placed in a
music warehouse in Cheapside, but he soon abandoned this employment to
become a singing actor at Covent Garden. On the 21st of May 1762 his
first work, an operetta entitled _The Shepherd's Artifice_, with words
and music by himself, was produced at this theatre. Other works
followed, his reputation being firmly established by the music to the
play of _The Padlock_, produced at Drury Lane under Garrick's management
in 1768, the composer himself taking the part of Mungo with conspicuous
success. He continued for some years to be connected with Drury Lane,
both as composer and as actor, and produced during this period two of
his best known works, _The Waterman_ (1774) and _The Quaker_ (1775). A
quarrel with Garrick led to the termination of his engagement. In _The
Comic Mirror_ he ridiculed prominent contemporary figures through the
medium of a puppet show. In 1782 he became joint manager of the Royal
circus, afterwards known as the Surrey theatre. In three years he lost
this position owing to a quarrel with his partner. His opera _Liberty
Hall_, containing the successful songs "Jock Ratlin," "The Highmettled
Racer," and "The Bells of Aberdovey," was produced at Drury Lane theatre
on the 8th of February 1785. In 1788 he sailed for the East Indies, but
the vessel having put in to Torbay in stress of weather, he changed his
mind and returned to London. In a musical variety entertainment called
_The Oddities_, he succeeded in winning marked popularity with a number
of songs that included "'Twas in the good ship 'Rover'," "Saturday Night
at Sea," "I sailed from the Downs in the 'Nancy,'" and the immortal "Tom
Bowling," written on the death of his eldest brother, Captain Thomas
Dibdin, at whose invitation he had planned his visit to India. A series
of monodramatic entertainments which he gave at his theatre, Sans Souci,
in Leicester Square, brought his songs, music and recitations more
prominently into notice, and permanently established his fame as a lyric
poet. It was at these entertainments that he first introduced many of
those sea-songs which so powerfully influenced the national spirit. The
words breathe the simple loyalty and dauntless courage that are the
cardinal virtues of the British sailor, and the music was appropriate
and naturally melodious. Their effect in stimulating and ennobling the
spirit of the navy during the war with France was so marked as to call
for special acknowledgment. In 1803 Dibdin was rewarded by government
with a pension of £200 a year, of which he was only for a time deprived
under the administration of Lord Grenville. During this period he opened
a music shop in the Strand, but the venture was a failure. Dibdin died
of paralysis in London on the 25th of July 1814. Besides his _Musical
Tour through England_ (1788), his _Professional Life_, an autobiography
published in 1803, a _History of the Stage_ (1795), and several smaller
works, he wrote upwards of 1400 songs and about thirty dramatic pieces.
He also wrote the following novels:--_The Devil_ (1785); _Hannah Hewitt_
(1792); _The Younger Brother_ (1793). An edition of his songs by G.
Hogarth (1843) contains a memoir of his life. His two sons, Charles and
Thomas John Dibdin (q.v.), whose works are often confused with those of
their father, were also popular dramatists in their day.




DIBDIN, THOMAS FROGNALL (1776-1847), English bibliographer, born at
Calcutta in 1776, was the son of Thomas Dibdin, the sailor brother of
Charles Dibdin. His father and mother both died on the way home to
England in 1780, and Thomas was brought up by a maternal uncle. He was
educated at St John's College, Oxford, and studied for a time at
Lincoln's Inn. After an unsuccessful attempt to obtain practice as a
provincial counsel at Worcester, he was ordained a clergyman at the
close of 1804, being appointed to a curacy at Kensington. It was not
until 1823 that he received the living of Exning in Sussex. Soon
afterwards he was appointed by Lord Liverpool to the rectory of St
Mary's, Bryanston Square, which he held until his death on the 18th of
November 1847. The first of his numerous bibliographical works was his
_Introduction to the Knowledge of Editions of the Classics_ (1802),
which brought him under the notice of the third Earl Spencer, to whom he
owed much important aid in his bibliographical pursuits. The rich
library at Althorp was thrown open to him; he spent much of his time in
it, and in 1814-1815 published his _Bibliotheca Spenceriana_. As the
library was not open to the general public, the information given in the
_Bibliotheca_ was found very useful, but since its author was unable
even to read the characters in which the books he described were
written, the work was marred by the errors which more or less
characterize all his productions. This fault of inaccuracy however was
less obtrusive in his series of playful, discursive works in the form of
dialogues on his favourite subject, the first of which, _Bibliomania_
(1809), was republished with large additions in 1811, and was very
popular, passing through numerous editions. To the same class belonged
the _Bibliographical Decameron_, a larger work, which appeared in 1817.
In 1810 he began the publication of a new and much extended edition of
Ames's _Typographical Antiquities_. The first volume was a great
success, but the publication was checked by the failure of the fourth
volume, and was never completed. In 1818 Dibdin was commissioned by
Earl Spencer to purchase books for him on the continent, an expedition
described in his sumptuous _Bibliographical, Antiquarian and Picturesque
Tour in France and Germany_ (1821). In 1824 he made an ambitious venture
in his _Library Companion, or the Young Man's Guide and Old Man's
Comfort in the Choice of a Library_, intended to point out the best
works in all departments of literature. His culture was not broad
enough, however, to render him competent for the task, and the work was
severely criticized. For some years Dibdin gave himself up chiefly to
religious literature. He returned to bibliography in his _Bibliophobia,
or Remarks on the Present Depression in the State of Literature and the
Book Trade_ (1832), and the same subject furnishes the main interest of
his _Reminiscences of a Literary Life_ (1836), and his _Bibliographical,
Antiquarian and Picturesque Tour in the Northern Counties of England and
Scotland_ (1838). Dibdin was the originator and vice-president, Lord
Spencer being the president, of the Roxburghe Club, founded in
1812,--the first of the numerous book clubs which have done such service
to literature.




DIBDIN, THOMAS JOHN (1771-1841), English dramatist and song-writer, son
of Charles Dibdin, the song-writer, and of Mrs Davenet, an actress whose
real name was Harriet Pitt, was born on the 21st of March 1771. He was
apprenticed to his maternal uncle, a London upholsterer, and later to
William Rawlins, afterwards sheriff of London. He summoned his second
master unsuccessfully for rough treatment; and after a few years of
service he ran away to join a company of country players. From 1789 to
1795 he played in all sorts of parts; he acted as scene painter at
Liverpool in 1791; and during this period he composed more than 1000
songs. He made his first attempt as a dramatic writer in _Something
New_, followed by _The Mad Guardian_ in 1795. He returned to London in
1795, having married two years before; and in the winter of 1798-1799
his _Jew and the Doctor_ was produced at Covent Garden. From this time
he contributed a very large number of comedies, operas, farces, &c., to
the public entertainment. Some of these brought immense popularity to
the writer and immense profits to the theatres. It is stated that the
pantomime of _Mother Goose_ (1807) produced more than £20,000 for the
management at Covent Garden theatre, and the _High-mettled Racer_,
adapted as a pantomime from his father's play, £18,000 at Astley's.
Dibdin was prompter and pantomime writer at Drury Lane until 1816, when
he took the Surrey theatre. This venture proved disastrous and he became
bankrupt. After this he was manager of the Haymarket, but without his
old success, and his last years were passed in comparative poverty. In
1827 he published two volumes of _Reminiscences_; and at the time of his
death he was preparing an edition of his father's sea songs, for which a
small sum was allowed him weekly by the lords of the admiralty. Of his
own songs "The Oak Table" and "The Snug Little Island" are well-known
examples. He died in London on the 16th of September 1841.




DIBRA (Slav. _Debra_), the capital of a sanjak bearing the same name, in
the vilayet of Monastir, eastern Albania, Turkey. Pop. (1900) about
15,000. Dibra occupies a valley enclosed by mountains, and watered by
the Tsrni Drin and Radika rivers, which meet 3 m. S. It is a fortified
city, and the only episcopal see of the Bulgarian exarchate in Albania;
most of the inhabitants are Albanians, but there is a strong Bulgarian
colony. The local trade is almost entirely agricultural.




DIBRUGARH, a town of British India, in the Lakhimpur district of eastern
Bengal and Assam, of which it is the headquarters, situated on the Dibru
river about 4 m. above its confluence with the Brahmaputra. Pop. (1901)
11,227. It is the terminus of steamer navigation on the Brahmaputra, and
also of a railway running to important coal-mines and petroleum wells,
which connects with the Assam-Bengal system. Large quantities of coal
and tea are exported. There are a military cantonment, the headquarters
of the volunteer corps known as the Assam Valley Light Horse; a
government high school, a training school for masters; and an aided
school for girls. In 1900 a medical school for the province was
established, out of a bequest left by Brigade-Surgeon J. Berry-White,
which is maintained by the government, to train hospital assistants for
the tea gardens. The Williamson artisan school is entirely supported by
an endowment.




DICAEARCHUS, of Messene in Sicily, Peripatetic philosopher and pupil of
Aristotle, historian, and geographer, flourished about 320 B.C. He was a
friend of Theophrastus, to whom he dedicated the majority of his works.
Of his writings, which comprised treatises on a great variety of
subjects, only the titles and a few fragments survive. The most
important of them was his [Greek: bios tês Hellados] (_Life in Greece_),
in which the moral, political and social condition of the people was
very fully discussed. In his _Tripoliticos_ he described the best form
of government as a mixture of monarchy, aristocracy and democracy, and
illustrated it by the example of Sparta. Among the philosophical works
of Dicaearchus may be mentioned the _Lesbiaci_, a dialogue in three
books, in which the author endeavours to prove that the soul is mortal,
to which he added a supplement called _Corinthiaci_. He also wrote a
_Description of the World_ illustrated by maps, in which was probably
included his _Measurements of Mountains_. A description of Greece (150
iambics, in C. Müller, _Frag. hist. Graec_. i. 238-243) was formerly
attributed to him, but, as the initial letters of the first twenty-three
lines show, was really the work of Dionysius, son of Calliphon. Three
considerable fragments of a prose description of Greece (Müller, i.
97-110) are now assigned to an unknown author named Heracleides. The _De
re publica_ of Cicero is supposed to be founded on one of Dicaearchus's
works.

  The best edition of the fragments is by M. Fuhr (1841), a work of
  great learning; see also a dissertation by F. G. Osann, _Beiträge zur
  röm. und griech. Litteratur_, ii. pp. 1-117 (1839); Pauly-Wissowa,
  _Realencyclopädie der klass. Altertumswiss_. v. pt. 1 (1905).




DICE (plural of die, O. Fr. _de_, derived from Lat. _dare_, to give),
small cubes of ivory, bone, wood or metal, used in gaming. The six sides
of a die are each marked with a different number of incised dots in such
a manner that the sum of the dots on any two opposite sides shall be 7.
Dice seem always to have been employed, as is the case to-day, for
gambling purposes, and they are also used in such games as backgammon.
There are many methods of playing, from one to five dice being used,
although two or three are the ordinary numbers employed in Great Britain
and America. The dice are thrown upon a table or other smooth surface
either from the hand or from a receptacle called a dice-box, the latter
method having been in common use in Greece, Rome and the Orient in
ancient times. Dice-boxes have been made in many shapes and of various
materials, such as wood, leather, agate, crystal, metal or paper. Many
contain bars within to ensure a proper agitation of the dice, and thus
defeat trickery. Some, formerly used in England, were employed with
unmarked dice, and allowed the cubes to fall through a kind of funnel
upon a board marked off into six equal parts numbered from 1 to 6. It is
a remarkable fact, that, wherever dice have been found, whether in the
tombs of ancient Egypt, of classic Greece, or of the far East, they
differ in no material respect from those in use to-day, the elongated
ones with rounded ends found in Roman graves having been, not dice but
_tali_, or knucklebones. Eight-sided dice have comparatively lately been
introduced in France as aids to children in learning the multiplication
table. The teetotum, or spinning die, used in many modern games, was
known in ancient times in China and Japan. The increased popularity of
the more elaborate forms of gaming has resulted in the decline of
dicing. The usual method is to throw three times with three dice. If one
or more sixes or fives are thrown the first time they may be reserved,
the other throws being made with the dice that are left. The object is
to throw three sixes = 18 or as near that number as possible, the
highest throw winning, or, when drinks are to be paid for, the lowest
throw losing. (For other methods of throwing consult the _Encyclopaedia
of Indoor Games_, by R. F. Foster, 1903.) The most popular form of pure
gambling with dice at the present day, particularly with the lower
classes in America, is _Craps_, or _Crap-Shooting_, a simple form of
_Hazard_, of French origin. Two dice are used. Each player puts up a
stake and the first caster may cover any or all of the bets. He then
_shoots_, i.e. throws the dice from his open hand upon the table. If the
sum of the dice is 7 or 11 the throw is a _nick_, or _natural_, and the
caster wins all stakes. If the throw is either 2, 3 or 12 it is a
_crap_, and the caster loses all. If any other number is thrown it is a
_point_, and the caster continues until he throws the same number again,
in which case he wins, or a 7, in which case he loses. The now
practically obsolete game of Hazard was much more complicated than
_Craps_. (Consult _The Game of Hazard Investigated_, by George Lowbut.)
_Poker dice_ are marked with ace, king, queen, jack and ten-spot. Five
are used and the object is, in three throws, to make pairs, triplets,
full hands or fours and fives of a kind, five aces being the highest
hand. Straights do not count. In throwing to decide the payment of
drinks the usual method is called _horse and horse_, in which the
highest throws retire, leaving the two lowest to decide the loser by the
best two in three throws. Should each player win one throw both are said
to be _horse and horse_, and the next throw determines the loser. The
two last casters may also agree to _sudden death_, i.e. a single throw.
_Loaded dice_, i.e. dice weighted slightly on the side of the lowest
number, have been used by swindlers from the very earliest times to the
present day, a fact proved by countless literary allusions. Modern dice
are often rounded at the corners, which are otherwise apt to wear off
irregularly.

_History._--Dice were probably evolved from knucklebones. The antiquary
Thomas Hyde, in his _Syntagma_, records his opinion that the game of
"odd or even," played with pebbles, is nearly coeval with the creation
of man. It is almost impossible to trace clearly the development of dice
as distinguished from knucklebones, on account of the confusing of the
two games by the ancient writers. It is certain, however, that both were
played in times antecedent to those of which we possess any written
records. Sophocles, in a fragment, ascribed their invention to
Palamedes, a Greek, who taught them to his countrymen during the siege
of Troy, and who, according to Pausanias (on Corinth, xx.), made an
offering of them on the altar of the temple of Fortune. Herodotus
(_Clio_) relates that the Lydians, during a period of famine in the days
of King Atys, invented dice, knucklebones and indeed all other games
except chess. The fact that dice have been used throughout the Orient
from time immemorial, as has been proved by excavations from ancient
tombs, seems to point clearly to an Asiatic origin. Dicing is mentioned
as an Indian game in the _Rig-veda_. In its primitive form knucklebones
was essentially a game of skill, played by women and children, while
dice were used for gambling, and it was doubtless the gambling spirit of
the age which was responsible for the derivative form of knucklebones,
in which four sides of the bones received different values, which were
then counted, like dice. Gambling with three, sometimes two, dice
([Greek: kuboi]) was a very popular form of amusement in Greece,
especially with the upper classes, and was an almost invariable
accompaniment to the symposium, or drinking banquet. The dice were cast
from conical beakers, and the highest throw was three sixes, called
_Aphrodite_, while the lowest, three aces, was called the _dog_. Both in
Greece and Rome different modes of counting were in vogue. Roman dice
were called _tesserae_ from the Greek word for four, indicative of the
four sides. The Romans were passionate gamblers, especially in the
luxurious days of the Empire, and dicing was a favourite form, though it
was forbidden except during the Saturnalia. The emperor Augustus wrote
in a letter to Suetonius concerning a game that he had played with his
friends: "Whoever threw a _dog_ or a six paid a _denarius_ to the bank
for every die, and whoever threw a _Venus_ (the highest) won
everything." In the houses of the rich the dice-beakers were of carved
ivory and the dice of crystal inlaid with gold. Mark Antony wasted his
time at Alexandria with dicing, while, according to Suetonius, the
emperors Augustus, Nero and Claudius were passionately fond of it, the
last named having written a book on the game. Caligula notoriously
cheated at the game; Domitian played it, and Commodus set apart special
rooms in his palace for it. The emperor Verus, adopted son of Antonine,
is known to have thrown dice whole nights together. Fashionable society
followed the lead of its emperors, and, in spite of the severity of the
laws, fortunes were squandered at the dicing table. Horace derided the
youth of the period, who wasted his time amid the dangers of dicing
instead of taming his charger and giving himself up to the hardships of
the chase. Throwing dice for money was the cause of many special laws in
Rome, according to one of which no suit could be brought by a person who
allowed gambling in his house, even if he had been cheated or assaulted.
Professional gamblers were common, and some of their loaded dice are
preserved in museums. The common public-houses were the resorts of
gamblers, and a fresco is extant showing two quarrelling dicers being
ejected by the indignant host. Virgil, in the _Copa_ generally ascribed
to him, characterizes the spirit of that age in verse, which has been
Englished as follows:--

  "What ho! Bring dice and good wine!
     Who cares for the morrow?
   Live--so calls grinning Death--
     Live, for I come to you soon!"

That the barbarians were also given to gaming, whether or not they
learned it from their Roman conquerors, is proved by Tacitus, who states
that the Germans were passionately fond of dicing, so much so, indeed,
that, having lost everything, they would even stake their personal
liberty. Centuries later, during the middle ages, dicing became the
favourite pastime of the knights, and both dicing schools (_scholae
deciorum_) and gilds of dicers existed. After the downfall of feudalism
the famous German mercenaries called _landsknechts_ established a
reputation as the most notorious dicing gamblers of their time. Many of
the dice of the period were curiously carved in the images of men and
beasts. In France both knights and ladies were given to dicing, which
repeated legislation, including interdictions on the part of St Louis in
1254 and 1256, did not abolish. In Japan, China, Korea, India and other
Asiatic countries dice have always been popular and are so still.

  See Foster's _Encyclopaedia of Indoor Games_ (1903); Raymond's
  _Illustriertes Knobelbrevier_ (Oranienburg, 1888); _Les Jeux des
  Anciens_, by L. Becq de Fouquières (Paris, 1869); _Das Knöchelspiel
  der Alten_, by Bolle (Wismar, 1886); _Die Spiele der Griechen und
  Römer_, by W. Richter (Leipzig, 1887); Raymond's _Alte und neue
  Würfelspiele_; _Chinese Games with Dice_, by Stewart Culin
  (Philadelphia, 1889); _Korean Games_, by Stewart Culin (Philadelphia,
  1895).




DICETO, RALPH DE (d. c. 1202), dean of St Paul's, London, and
chronicler, is first mentioned in 1152, when he received the
archdeaconry of Middlesex. He was probably born between 1120 and 1130;
of his parentage and nationality we know nothing. The common statement
that he derived his surname from Diss in Norfolk is a mere conjecture;
Dicetum may equally well be a Latinized form of Dissai, or Dicy, or
Dizy, place names which are found in Maine, Picardy, Burgundy and
Champagne. In 1152 Diceto was already a master of arts; presumably he
had studied at Paris. His reputation for learning and integrity stood
high; he was regarded with respect and favour by Arnulf of Lisieux and
Gilbert Foliot of Hereford (afterwards of London), two of the most
eminent bishops of their time. Quite naturally, the archdeacon took in
the Becket question the same side as his friends. Although his narrative
is colourless, and although he was one of those who showed some sympathy
for Becket at the council of Northampton (1164), the correspondence of
Diceto shows that he regarded the archbishop's conduct as
ill-considered, and that he gave advice to those whom Becket regarded as
his chief enemies. Diceto was selected, in 1166, as the envoy of the
English bishops when they protested against the excommunications
launched by Becket. But, apart from this episode, which he
characteristically omits to record, he remained in the background. The
natural impartiality of his intellect was accentuated by a certain
timidity, which is apparent in his writings no less than in his life.
About 1180 he became dean of St Paul's. In this office he distinguished
himself by careful management of the estates, by restoring the
discipline of the chapter, and by building at his own expense a
deanery-house. A scholar and a man of considerable erudition, he showed
a strong preference for historical studies; and about the time when he
was preferred to the deanery he began to collect materials for the
history of his own times. His friendships with Richard Fitz Nigel, who
succeeded Foliot in the see of London, with William Longchamp, the
chancellor of Richard I., and with Walter of Coutances, the archbishop
of Rouen, gave him excellent opportunities of collecting information.
His two chief works, the _Abbreviationes Chronicorum_ and the _Ymagines
Historiarum_, cover the history of the world from the birth of Christ to
the year 1202. The former, which ends in 1147, is a work of learning and
industry, but almost entirely based upon extant sources. The latter,
beginning as a compilation from Robert de Monte and the letters of
Foliot, becomes an original authority about 1172, and a contemporary
record about 1181. In precision and fulness of detail the _Ymagines_ are
inferior to the chronicles of the so-called Benedict and of Hoveden.
Though an annalist, Diceto is careless in his chronology; and the
documents which he incorporates, while often important, are selected on
no principle. He has little sense of style; but displays considerable
insight when he ventures to discuss a political situation. For this
reason, and on account of the details with which they supplement the
more important chronicles of the period, the _Ymagines_ are a valuable
though a secondary source.

  See W. Stubbs' edition of the _Historical Works_ of Diceto (Rolls ed.
  1876, 2 vols.), and especially the introduction. The second volume
  contains minor works which are the barest compendia of facts taken
  from well-known sources. Diceto's fragmentary Domesday of the
  capitular estates has been edited by Archdeacon Hale in _The Domesday
  of St Paul's_, pp. 109 ff. (Camden Society, 1858).




DICEY, EDWARD (1832- ), English writer, son of T. E. Dicey of Claybrook
Hall, Leicestershire, was born in 1832. Educated at Trinity College,
Cambridge, where he took mathematical and classical honours, he became
an active journalist, contributing largely to the principal reviews. He
was called to the bar in 1875, became a bencher of Gray's Inn in 1896,
and was treasurer in 1903-1904. He was connected with the _Daily
Telegraph_ as leader writer and then as special correspondent, and after
a short spell in 1870 as editor of the _Daily News_ he became editor of
the _Observer_, a position which he held until 1889. Of his many books
on foreign affairs perhaps the most important are his _England and
Egypt_ (1884), _Bulgaria, the Peasant State_ (1895), _The Story of the
Khedivate_ (1902), and _The Egypt of the Future_ (1907). He was created
C.B. in 1886.

His brother ALBERT VENN DICEY (b. 1835), English jurist, was educated at
Balliol College, Oxford, where he took a first class in the classical
schools in 1858. He was called to the bar at the Inner Temple in 1863.
He held fellowships successively at Balliol, Trinity and All Souls', and
from 1882 to 1909 was Vinerian professor of law. He became Q.C. in 1890.
His chief works are the _Introduction to the Study of the Law of the
Constitution_ (1885, 6th ed. 1902), which ranks as a standard work on
the subject; _England's Case against Home Rule_ (1886); _A Digest of the
Law of England with Reference to the Conflict of Laws_ (1896), and
_Lectures on the Relation between Law and Public Opinion in England
during the 19th century_ (1905).




DICHOTOMY (Gr. [Greek: dicha], apart, [Greek: temnein], to cut),
literally a cutting asunder, the technical term for a form of logical
division, consisting in the separation of a genus into two species, one
of which has and the other has not, a certain quality or attribute. Thus
men may be thus divided into white men, and men who are not white; each
of these may be subdivided similarly. On the principle of contradiction
this division is both exhaustive and exclusive; there can be no
overlapping, and no members of the original genus or the lower groups
are omitted. This method of classification, though formally accurate,
has slight value in the exact sciences, partly because at every step one
of the two groups is merely negatively characterized and therefore
incapable of real subdivision; it is useful, however, in setting forth
clearly the gradual descent from the most inclusive genus (_summum
genus_) through species to the lowest class (_infima species_), which is
divisible only into individual persons or things. (See further
DIVISION.) In astronomy the term is used for the aspect of the moon or
of a planet when apparently half illuminated, so that its disk has the
form of a semicircle.




DICK, ROBERT (1811-1866), Scottish geologist and botanist, was born at
Tullibody, in Clackmannanshire, in January 1811. His father was an
officer of excise. At the age of thirteen, after receiving a good
elementary education at the parish school, Robert Dick was apprenticed
to a baker, and served for three years. In these early days he became
interested in wild flowers--he made a collection of plants and gradually
acquired some knowledge of their names from an old encyclopaedia. When
his time was out he left Tullibody and gained employment as a journeyman
baker at Leith, Glasgow and Greenock. Meanwhile his father, who in 1826
had been removed to Thurso, as supervisor of excise, advised his son to
set up a baker's shop in that town. Thither Robert Dick went in 1830, he
started in business as a baker and worked laboriously until he died on
the 24th of December 1866. Throughout this period he zealously devoted
himself to studying and collecting the plants, mollusca and insects of a
wide area of Caithness, and his attention was directed soon after he
settled in Thurso to the rocks and fossils. In 1835 he first found
remains of fossil fishes; but it was not till some years later that his
interest became greatly stirred. Then he obtained a copy of Hugh
Miller's _Old Red Sandstone_ (published in 1841), and he began
systematically to collect with hammer and chisel the fossils from the
Caithness flags. In 1845 he found remains of _Holoptychius_ and
forwarded specimens to Hugh Miller, and he continued to send the best of
his fossil fishes to that geologist, and to others after the death of
Miller. In this way he largely contributed to the progress of geological
knowledge, although he himself published nothing and was ever averse
from publicity. His herbarium, which consisted of about 200 folios of
mosses, ferns and flowering plants "almost unique in its completeness,"
is now stored, with many of his fossils, in the museum at Thurso. Dick
had a hard struggle for existence, especially through competition during
his late years, when he was reduced almost to beggary: but of this few,
if any, of his friends were aware until it was too late. A monument
erected in the new cemetery at Thurso testifies to the respect which his
life-work created, when the merits of this enthusiastic naturalist came
to be appreciated.

  See _Robert Dick, Baker of Thurso, Geologist and Botanist_, by Samuel
  Smiles (1878).




DICK, THOMAS (1774-1857), Scottish writer on astronomy, was born at
Dundee on the 24th of November 1774. The appearance of a brilliant
meteor inspired him, when in his ninth year, with a passion for
astronomy; and at the age of sixteen he forsook the loom, and supported
himself by teaching. In 1794 he entered the university of Edinburgh, and
set up a school o

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