Curiosities of Science, Past and Present
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Title: Curiosities of Science, Past and Present
Author: John Timbs
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*** START OF THE PROJECT GUTENBERG EBOOK CURIOSITIES OF SCIENCE, PAST AND PRESENT ***
NEW WORK ON PAINTING.
_Just ready, in small 8vo, with Frontispiece and Vignette_,
PAINTING
POPULARLY EXPLAINED;
WITH
The Practice of the Art,
AND
HISTORICAL NOTICES OF ITS PROGRESS.
BY
THOMAS J. GULLICK, PAINTER,
AND
JOHN TIMBS, F.S.A.
The plan of this work is thus sketched in the _Introduction_:
“There have been in the history of Art, four grand styles of
imitating Nature--Tempera, Encaustic, Fresco, and Oil. These,
together with the minor modes of Painting, we propose arranging
in something like chronological sequence; but our design being
to offer an explanation of the Art derived from practical
acquaintance, rather than attempt to give its history, we shall
confine ourselves for the most part to so much only of the History
of Painting as is necessary to elucidate the origin of the
different practices which have obtained at different periods.”
By this means, the Authors hope to produce a work which may be
valuable to the Amateur, and interesting to the Connoisseur, the
Artist, and the General Reader.
LONDON: KENT & CO. (LATE BOGUE), FLEET STREET.
[Illustration: MOUTH OF THE GREAT ROSSE TELESCOPE, AT PARSONSTOWN.
FROM A PHOTOGRAPH.]
Things not generally Known
Familiarly Explained.
CURIOSITIES OF SCIENCE,
Past and Present.
A BOOK FOR OLD AND YOUNG.
BY JOHN TIMBS, F.S.A.
AUTHOR OF THINGS NOT GENERALLY KNOWN; AND EDITOR OF THE
YEAR-BOOK OF FACTS.
[Illustration: Model of the Safety-Lamp, made by Sir Humphry
Davy’s own hands; in the possession of the Royal Society.]
LONDON:
KENT AND CO. (LATE BOGUE), FLEET STREET.
MDCCCLVIII.
_The Author reserves the right of authorising a Translation of
this Work._
LONDON:
PRINTED BY LEVEY, ROBSON, AND FRANKLYN,
Great New Street and Fetter Lane.
GENTLE READER,
The volume of “CURIOSITIES” which I here present to your notice is a
portion of the result of a long course of reading, observation, and
research, necessary for the compilation of thirty volumes of “Arcana
of Science” and “Year-Book of Facts,” published from 1828 to 1858.
Throughout this period--nearly half of the Psalmist’s “days of our
years”--I have been blessed with health and strength to produce these
volumes, year by year (with one exception), upon the appointed day; and
this with unbroken attention to periodical duties, frequently rendered
harassing or ungenial. Nevertheless, during these three decades I
have found my account in the increasing approbation of the reading
public, which has been so largely extended to the series of “THINGS
NOT GENERALLY KNOWN,” of which the present volume of “CURIOSITIES OF
SCIENCE” is an instalment. I need scarcely add, that in its progressive
preparation I have endeavoured to compare, weigh, and consider,
the contents, so as to combine the experience of the Past with the
advantages of the Present.
In these days of universal attainments, when Science becomes not
merely a luxury to the rich, but bread to the poor, and when the
very amusements as well as the conveniences of life have taken a
scientific colour, it is reasonable to hope that the present volume
may be acceptable to a large class of seekers after “things not
generally known.” For this purpose, I have aimed at soundness as well
as popularity; although, for myself, I can claim little beyond being
one of those industrious “ants of science” who garner facts, and by
selection and comparison adapt them for a wider circle of readers
than they were originally expected to reach. In each case, as far as
possible, these “CURIOSITIES” bear the mint-mark of authority; and in
the living list are prominent the names of Humboldt and Herschel, Airy
and Whewell, Faraday, Brewster, Owen, and Agassiz, Maury, Wheatstone,
and Hunt, from whose writings and researches the following pages are
frequently enriched.
The sciences here illustrated are, in the main, Astronomy and
Meteorology; Geology and Paleontology; Physical Geography; Sound,
Light, and Heat; Magnetism and Electricity,--the latter with special
attention to the great marvel of our times, the Electro-magnetic
Telegraph. I hope, at no very distant period, to extend the
“CURIOSITIES” to another volume, to include branches of Natural and
Experimental Science which are not here presented.
I. T.
_November 1858._
CONTENTS.
PAGE
INTRODUCTORY 1-10
PHYSICAL PHENOMENA 11-26
SOUND AND LIGHT 27-53
ASTRONOMY 54-103
GEOLOGY AND PALEONTOLOGY 104-145
METEOROLOGICAL PHENOMENA 146-169
PHYSICAL GEOGRAPHY OF THE SEA 170-192
MAGNETISM AND ELECTRICITY 193-219
THE ELECTRIC TELEGRAPH 220-228
MISCELLANEA 229-241
The Frontispiece.
THE GREAT ROSSE TELESCOPE.
The originator and architect of this magnificent instrument had long
been distinguished in scientific research as Lord Oxmantown; and
may be considered to have gracefully commemorated his succession to
the Earldom of Rosse, and his Presidency of the Royal Society, by
the completion of this marvellous work, with which his name will be
hereafter indissolubly associated.
The Great Reflecting Telescope at Birr Castle (of which the
Frontispiece represents a portion[1]) will be found fully described at
pp. 96-99 of the present volume of _Curiosities of Science_.
This matchless instrument has already disclosed “forms of stellar
arrangement indicating modes of dynamic action never before
contemplated in celestial mechanics.” “In these departments of
research,--the examination of the configurations of nebulæ, and the
resolution of nebulæ into stars (says the Rev. Dr. Scoresby),--the
six-feet speculum has had its grandest triumphs, and the noble
artificer and observer the highest rewards of his talents and
enterprise. Altogether, the quantity of work done during a period of
about seven years--including a winter when a noble philanthropy for
a starving population absorbed the keenest interests of science--has
been decidedly great; and the new knowledge acquired concerning the
handiwork of the great Creator amply satisfying of even sanguine
expectation.”
The Vignette.
SIR HUMPHRY DAVY’S OWN MODEL OF HIS SAFETY-LAMP.
Of the several contrivances which have been proposed for safely
lighting coal-mines subject to the visitation of fire-damp, or
carburetted hydrogen, the Safety-Lamp of Sir Humphry Davy is the only
one which has ever been judged safe, and been extensively employed. The
inventor first turned his attention to the subject in 1815, when Davy
began a minute chemical examination of fire-damp, and found that it
required an admixture of a large quantity of atmospheric air to render
it explosive. He then ascertained that explosions of inflammable gases
were incapable of being passed through long narrow metallic tubes, and
that this principle of security was still obtained by diminishing their
length and increasing their number. This fact led to trials upon sieves
made of wire-gauze; when Davy found that if a piece of wire-gauze was
held over the flame of a lamp, or of coal-gas, it prevented the flame
from passing; and he ascertained that a flame confined in a cylinder of
very fine wire-gauze did not explode even in a mixture of oxygen and
hydrogen, but that the gases burnt in it with great vivacity.
These experiments served as the basis of the Safety-Lamp. The apertures
in the gauze, Davy tells us in his work on the subject, should not
be more than 1/22d of an inch square. The lamp is screwed on to the
bottom of the wire-gauze cylinder. When it is lighted, and gradually
introduced into an atmosphere mixed with fire-damp, the size and length
of the flame are first increased. When the inflammable gas forms as
much as 1/12th of the volume of air, the cylinder becomes filled with a
feeble blue flame, within which the flame of the wick burns brightly,
and the light of the wick continues till the fire-damp increases to
1/6th or 1/5th; it is then lost in the flame of the fire-damp, which
now fills the cylinder with a pretty strong light; and when the foul
air constitutes one-third of the atmosphere it is no longer fit for
respiration,--and this ought to be a signal to the miner to leave that
part of the workings.
Sir Humphry Davy presented his first communication respecting his
discovery of the Safety-Lamp to the Royal Society in 1815. This was
followed by a series of papers remarkable for their simplicity and
clearness, crowned by that read on the 11th of January 1816, when the
principle of the Safety-Lamp was announced, and Sir Humphry presented
to the Society a model made by his own hands, which is to this day
preserved in the collection of the Royal Society at Burlington House.
From this interesting memorial the Vignette has been sketched.
There have been several modifications of the Safety-Lamp, and the merit
of the discovery has been claimed by others, among whom was Mr. George
Stephenson; but the question was set at rest forty-one years since by
an examination,--attested by Sir Joseph Banks, P.R.S., Mr. Brande, Mr.
Hatchett, and Dr. Wollaston,--and awarding the independent merit to
Davy.
A more substantial, though not a more honourable, testimony of approval
was given by the coal-owners, who subscribed 2500_l._ to purchase a
superb service of plate, which was suitably inscribed and presented to
Davy.[2]
Meanwhile the Report by the Parliamentary Committee “cannot admit that
the experiments (made with the Lamp) have any tendency to detract from
the character of Sir Humphry Davy, or to disparage the fair value
placed by himself upon his invention. The improvements are probably
those which longer life and additional facts would have induced him to
contemplate as desirable, and of which, had he not been the inventor,
he might have become the patron.”
The principle of the invention may be thus summed up. In the
Safety-Lamp, the mixture of the fire-damp and atmospheric air within
the cage of wire-gauze explodes upon coming in contact with the flame;
but the combustion cannot pass through the wire-gauze, and being there
imprisoned, cannot impart to the explosive atmosphere of the mine any
of its force. This effect has been erroneously attributed to a cooling
influence of the metal.
Professor Playfair has eloquently described the Safety-Lamp of Davy as
a present from philosophy to the arts; a discovery in no degree the
effect of accident or chance, but the result of patient and enlightened
research, and strongly exemplifying the great use of an immediate and
constant appeal to experiment. After characterising the invention as
the _shutting-up in a net of the most slender texture_ a most violent
and irresistible force, and a power that in its tremendous effects
seems to emulate the lightning and the earthquake, Professor Playfair
thus concludes: “When to this we add the beneficial consequences, and
the saving of the lives of men, and consider that the effects are to
remain as long as coal continues to be dug from the bowels of the
earth, it may be fairly said that there is hardly in the whole compass
of art or science a single invention of which one would rather wish
to be the author.... This,” says Professor Playfair, “is exactly such
a case as we should choose to place before Bacon, were he to revisit
the earth; in order to give him, in a small compass, an idea of the
advancement which philosophy has made since the time when he had
pointed out to her the route which she ought to pursue.”
CURIOSITIES OF SCIENCE.
Introductory.
SCIENCE OF THE ANCIENT WORLD.
In every province of human knowledge where we now possess a careful
and coherent interpretation of nature, men began by attempting in
bold flights to leap from obvious facts to the highest point of
generality--to some wide and simple principle which after-ages had to
reject. Thus, from the facts that all bodies are hot or cold, moist or
dry, they leapt at once to the doctrine that the world is constituted
of four elements--earth, air, fire, water; from the fact that the
heavenly bodies circle the sky in courses which occur again and again,
they at once asserted that they move in exact circles, with an exactly
uniform motion; from the fact that heavy bodies fall through the air
somewhat faster than light ones, it was assumed that all bodies fall
quickly or slowly exactly in proportion to their weight; from the fact
that the magnet attracts iron, and that this force of attraction is
capable of increase, it was inferred that a perfect magnet would have
an irresistible force of attraction, and that the magnetic pole of
the earth would draw the nails out of a ship’s bottom which came near
it; from the fact that some of the finest quartz crystals are found
among the snows of the Alps, it was inferred that the crystallisation
of gems is the result of intense and long-continued cold: and so on
in innumerable instances. Such anticipations as these constituted
the basis of almost all the science of the ancient world; for such
principles being so assumed, consequences were drawn from them with
great ingenuity, and systems of such deductions stood in the place of
science.--_Edinburgh Review_, No. 216.
SCIENCE AT OXFORD AND CAMBRIDGE.
The earliest science of a decidedly English school is due, for the most
part, to the University of Oxford, and specially to Merton College,--a
foundation of which Wood remarks, that there was no other for two
centuries, either in Oxford or Paris, which could at all come near it
in the cultivation of the sciences. But he goes on to say that large
chests full of the writers of this college were allowed to remain
untouched by their successors for fear of the magic which was supposed
to be contained in them. Nevertheless, it is not difficult to trace
the liberalising effect of scientific study upon the University in
general, and Merton College in particular; and it must be remembered
that to the cultivation of the mind at Oxford we owe almost all the
literary celebrity of the middle ages. In this period the University of
Cambridge appears to have acquired no scientific distinction. Taking
as a test the acquisition of celebrity on the continent, we find that
Bacon, Sacrobosco, Greathead, Estwood, &c. were all of Oxford. The
latter University had its morning of splendour while Cambridge was
comparatively unknown; it had also its noonday, illustrated by such men
as Briggs, Wren, Wallis, Halley, and Bradley.
The age of science at Cambridge may be said to have begun with Francis
Bacon; and but that we think much of the difference between him and
his celebrated namesake lies more in time and circumstances than in
talents or feelings, we would rather date from 1600 with the former
than from 1250 with the latter. Praise or blame on either side is out
of the question, seeing that the earlier foundation of Oxford, and its
superiority in pecuniary means, rendered all that took place highly
probable; and we are in a great measure indebted for the liberty of
writing our thoughts, to the cultivation of the liberalising sciences
at Oxford in the dark ages.
With regard to the University of Cambridge, for a long time there
hardly existed the materials of any proper instruction, even to the
extent of pointing out what books should be read by a student desirous
of cultivating astronomy.
PLATO’S SURVEY OF THE SCIENCES.
Plato, like Francis Bacon, took a review of the sciences of his
time: he enumerates arithmetic and plane geometry, treated as
collections of abstract and permanent truths; solid geometry, which
he “notes as deficient” in his time, although in fact he and his
school were in possession of the doctrine of the “five regular
solids;” astronomy, in which he demands a science which should
be elevated above the mere knowledge of phenomena. The visible
appearances of the heavens only suggest the problems with which
true astronomy deals; as beautiful geometrical diagrams do not
prove, but only suggest geometrical propositions. Finally, Plato
notices the subject of harmonics, in which he requires a science
which shall deal with truths more exact than the ear can establish,
as in astronomy he requires truths more exact than the eye can
assure us of.
In a subsequent paper Plato speaks of _Dialectic_ as a still
higher element of a philosophical education, fitted to lead men
to the knowledge of real existences and of the supreme good. Here
he describes dialectic by its objects and purpose. In other places
dialectic is spoken of as a method or process of analysis; as in
the _Phædrus_, where Socrates describes a good dialectician as one
who can divide a subject according to its natural members, and not
miss the joint, like a bad carver. Xenophon says that Socrates
derived _dialectic_ from a term implying to _divide a subject into
parts_, which Mr. Grote thinks unsatisfactory as an etymology, but
which has indicated a practical connection in the Socratic school.
The result seems to be that Plato did not establish any method of
analysis of a subject as his dialectic; but he conceived that the
analytical habits formed by the comprehensive study of the exact
sciences, and sharpened by the practice of dialogue, would lead his
students to the knowledge of first principles.--_Dr. Whewell._
FOLLY OF ATHEISM.
Morphology, in natural science, teaches us that the whole animal
and vegetable creation is formed upon certain fundamental types
and patterns, which can be traced under various modifications and
transformations through all the rich variety of things apparently of
most dissimilar build. But here and there a scientific person takes
it into his foolish head that there may be a set of moulds without
a moulder, a calculated gradation of forms without a calculator, an
ordered world without an ordering God. Now, this atheistical science
conveys about as much meaning as suicidal life: for science is possible
only where there are ideas, and ideas are only possible where there is
mind, and minds are the offspring of God; and atheism itself is not
merely ignorance and stupidity,--it is the purely nonsensical and the
unintelligible.--_Professor Blackie_; _Edinburgh Essays_, 1856.
THE ART OF OBSERVATION.
To observe properly in the very simplest of the physical sciences
requires a long and severe training. No one knows this so feelingly
as the great discoverer. Faraday once said, that he always doubts his
own observations. Mitscherlich on one occasion remarked to a man of
science that it takes fourteen years to discover and establish a single
new fact in chemistry. An enthusiastic student one day betook himself
to Baron Cuvier with the exhibition of a new organ--a muscle which he
supposed himself to have discovered in the body of some living creature
or other; but the experienced and sagacious naturalist kindly bade the
young man return to him with the same discovery in six months. The
Baron would not even listen to the student’s demonstration, nor examine
his dissection, till the eager and youthful discoverer had hung over
the object of inquiry for half a year; and yet that object was a mere
thing of the senses.--_North-British Review_, No. 18.
MUTUAL RELATIONS OF PHENOMENA.
In the observation of a phenomenon which at first sight appears to
be wholly isolated, how often may be concealed the germ of a great
discovery! Thus, when Galvani first stimulated the nervous fibre of
the frog by the accidental contact of two heterogeneous metals, his
contemporaries could never have anticipated that the action of the
voltaic pile would discover to us in the alkalies metals of a silver
lustre, so light as to swim on water, and eminently inflammable; or
that it would become a powerful instrument of chemical analysis, and at
the same time a thermoscope and a magnet. When Huyghens first observed,
in 1678, the phenomenon of the polarisation of light, exhibited in the
difference between two rays into which a pencil of light divides itself
in passing through a doubly refracting crystal, it could not have been
foreseen that a century and a half later the great philosopher Arago
would, by his discovery of _chromatic polarisation_, be led to discern,
by means of a small fragment of Iceland spar, whether solar light
emanates from a solid body or a gaseous covering; or whether comets
transmit light directly, or merely by reflection.--_Humboldt’s Cosmos_,
vol. i.
PRACTICAL RESULTS OF THEORETICAL SCIENCE.
What are the great wonders, the great sources of man’s material
strength, wealth, and comfort in modern times? The Railway, with its
mile-long trains of men and merchandise, moving with the velocity of
the wind, and darting over chasms a thousand feet wide; the Electric
Telegraph, along which man’s thoughts travel with the velocity of
light, and girdle the earth more quickly than Puck’s promise to his
master; the contrivance by which the Magnet, in the very middle of
a strip of iron, is still true to the distant pole, and remains a
faithful guide to the mariner; the Electrotype process, by which a
metallic model of any given object, unerringly exact, grows into
being like a flower. Now, all these wonders are the result of recent
and profound discoveries in theoretical science. The Locomotive
Steam-engine, and the Steam-engine in all its other wonderful and
invaluable applications, derives its efficacy from the discoveries, by
Watt and others, of the laws of steam. The Railway Bridge is not made
strong by mere accumulation of materials, but by the most exact and
careful scientific examination of the means of giving the requisite
strength to every part, as in the great example of Mr. Stephenson’s
Britannia Bridge over the Menai Strait. The Correction of the Magnetic
Needle in iron ships it would have been impossible for Mr. Airy to
secure without a complete theoretical knowledge of the laws of
Magnetism. The Electric Telegraph and the Electrotype process include
in their principles and mechanism the most complete and subtle results
of electrical and magnetical theory.--_Edinburgh Review_, No. 216.
PERPETUITY OF IMPROVEMENT.
In the progress of society all great and real improvements are
perpetuated: the same corn which, four thousand years ago, was raised
from an improved grass by an inventor worshiped for two thousand years
in the ancient world under the name of Ceres, still forms the principal
food of mankind; and the potato, perhaps the greatest benefit that the
old has derived from the new world, is spreading over Europe, and will
continue to nourish an extensive population when the name of the race
by whom it was first cultivated in South America is forgotten.--_Sir H.
Davy._
THE EARLIEST ENGLISH SCIENTIFIC TREATISE.
Geoffrey Chaucer, the poet, wrote a treatise on the Astrolabe for his
son, which is the earliest English treatise we have met with on any
scientific subject. It was not completed; and the apologies which
Chaucer makes to his own child for writing in English are curious;
while his inference that his son should therefore “pray God save the
king that is lord of this language,” is at least as loyal as logical.
PHILOSOPHERS’ FALSE ESTIMATES OF THEIR OWN LABOURS.
Galileo was confident that the most important part of his contributions
to the knowledge of the solar system was his Theory of the Tides--a
theory which all succeeding astronomers have rejected as utterly
baseless and untenable. Descartes probably placed far above his
beautiful explanation of the rainbow, his _à priori_ theory of the
existence of the vortices which caused the motion of the planets and
satellites. Newton perhaps considered as one of the best parts of his
optical researches his explanation of the natural colour of bodies,
which succeeding optical philosophers have had to reject; and he
certainly held very strongly the necessity of a material cause for
gravity, which his disciples have disregarded. Davy looked for his
greatest triumph in the application of his discoveries to prevent
the copper bottoms of ships from being corroded. And so in other
matters.--_Edinburgh Review_, No. 216.
RELICS OF GENIUS.
Professor George Wilson, in a lecture to the Scottish Society of
Arts, says: “The spectacle of these things ministers only to the
good impulses of humanity. Isaac Newton’s telescope at the Royal
Society of London; Otto Guericke’s air-pump in the Library at Berlin;
James Watt’s repaired Newcomen steam-engine in the Natural-Philosophy
class-room of the College at Glasgow; Fahrenheit’s thermometer in
the corresponding class-room of the University of Edinburgh; Sir H.
Davy’s great voltaic battery at the Royal Institution, London, and
his safety-lamp at the Royal Society; Joseph Black’s pneumatic trough
in Dr. Gregory’s possession; the first wire which Faraday made rotate
electro-magnetically, at St. Bartholomew’s Hospital; Dalton’s atomic
models at Manchester; and Kemp’s liquefied gases in the Industrial
Museum of Scotland,--are alike personal relics, historical monuments,
and objects of instruction, which grow more and more precious every
year, and of which we never can have too many.”
THE ROYAL SOCIETY: THE NATURAL AND SUPERNATURAL.
The Royal Society was formed with the avowed object of increasing
knowledge by direct experiment; and it is worthy of remark, that the
charter granted by Charles II. to this celebrated institution declares
that its object is the extension of natural knowledge, as opposed to
that which is supernatural.
Dr. Paris (_Life of Sir H. Davy_, vol. ii. p. 178) says: “The charter
of the Royal Society states that it was established for the improvement
of _natural_ science. This epithet _natural_ was originally intended to
imply a meaning, of which very few persons, I believe, are aware. At
the period of the establishment of the society, the arts of witchcraft
and divination were very extensively encouraged; and the word _natural_
was therefore introduced in contradistinction to _supernatural_.”
THE PHILOSOPHER BOYLE.
After the death of Bacon, one of the most distinguished Englishmen
was certainly Robert Boyle, who, if compared with his contemporaries,
may be said to rank immediately below Newton, though of course very
inferior to him as an original thinker. Boyle was the first who
instituted exact experiments into the relation between colour and heat;
and by this means not only ascertained some very important facts, but
laid a foundation for that union between optics and thermotics, which,
though not yet completed, now merely waits for some great philosopher
to strike out a generalisation large enough to cover both, and thus
fuse the two sciences into a single study. It is also to Boyle, more
than to any other Englishman, that we owe the science of hydrostatics
in the state in which we now possess it.[3] He is also the original
discoverer of that beautiful law, so fertile in valuable results,
according to which the elasticity of air varies as its density. And,
in the opinion of one of the most eminent modern naturalists, it was
Boyle who opened up those chemical inquiries which went on accumulating
until, a century later, they supplied the means by which Lavoisier and
his contemporaries fixed the real basis of chemistry, and enabled it
for the first time to take its proper stand among those sciences that
deal with the external world.--_Buckle’s History of Civilization_, vol.
i.
SIR ISAAC NEWTON’S ROOMS AND LABORATORY IN TRINITY COLLEGE, CAMBRIDGE.
Of the rooms occupied by Newton during his early residence at
Cambridge, it is now difficult to settle the locality. The chamber
allotted to him as Fellow, in 1667, was “the Spiritual Chamber,”
conjectured to have been the ground-room, next the chapel, but it is
not certain that he resided there. The rooms in which he lived from
1682 till he left Cambridge, are in the north-east corner of the great
court, on the first floor, on the right or north of the gateway or
principal entrance to the college. His laboratory, as Dr. Humphrey
Newton tell us, was “on the left end of the garden, near the east end
of the chapel; and his telescope (refracting) was five feet long, and
placed at the head of the stairs, going down into the garden.”[4] The
east side of Newton’s rooms has been altered within the last fifty
years: Professor Sedgwick, who came up to college in 1804, recollects a
wooden room, supported on an arcade, shown in Loggan’s view, in place
of which arcade is now a wooden wall and brick chimney.
Dr. Humphrey Newton relates that in college Sir Isaac very rarely
went to bed till two or three o’clock in the morning, sometimes
not till five or six, especially at spring and fall of the leaf,
when he used to employ about six weeks in his laboratory, the
fire scarcely going out either night or day; he sitting up one
night, and Humphrey another, till he had finished his chemical
experiments. Dr. Newton describes the laboratory as “well furnished
with chymical materials, as bodyes, receivers, heads, crucibles,
&c., which was made very little use of, ye crucibles excepted,
in which he fused his metals: he would sometimes, though very
seldom, look into an old mouldy book, which lay in his laboratory;
I think it was titled _Agricola de Metallis_, the transmuting of
metals being his chief design, for which purpose antimony was a
great ingredient.” “His brick furnaces, _pro re nata_, he made and
altered himself without troubling a bricklayer.” “What observations
he might make with his telescope, I know not, but several of his
observations about comets and the planets may be found scattered
here and there in a book intitled _The Elements of Astronomy_, by
Dr. David Gregory.”[5]
NEWTON’S “APPLE-TREE.”
Curious and manifold as are the trees associated with the great names
of their planters, or those who have sojourned in their shade, the
Tree which, by the falling of its fruit, suggested to Newton the idea
of Gravity, is of paramount interest. It appears that, in the autumn
of 1665, Newton left his college at Cambridge for his paternal home
at Woolsthorpe. “When sitting alone in the garden,” says Sir David
Brewster, “and speculating on the power of gravity, it occurred to him,
that as the same power by which the apple fell to the ground was not
sensibly diminished at the greatest distance from the centre of the
earth to which we can reach, neither at the summits of the loftiest
spires, nor on the tops of the highest mountains, it might extend to
the moon and retain her in her orbit, in the same manner as it bends
into a curve a stone or a cannon-ball when projected in a straight line
from the surface of the earth.”--_Life of Newton_, vol. i. p. 26. Sir
David Brewster notes, that neither Pemberton nor Whiston, who received
from Newton himself his first ideas of gravity, records this story of
the falling apple. It was mentioned, however, to Voltaire by Catherine
Barton, Newton’s niece; and to Mr. Green by Martin Folkes, President
of the Royal Society. Sir David Brewster saw the reputed apple-tree in
1814, and brought away a portion of one of its roots. The tree was so
much decayed that it was cut down in 1820, and the wood of it carefully
preserved by Mr. Turnor, of Stoke Rocheford.
De Morgan (in _Notes and Queries_, 2d series, No. 139, p. 169)
questions whether the fruit was an apple, and maintains that the
anecdote rests upon very slight authority; more especially as
the idea had for many years been floating before the minds of
physical inquirers; although Newton cleared away the confusions and
difficulties which prevented very able men from proceeding beyond
conjecture, and by this means established _universal_ gravitation.
NEWTON’S “PRINCIPIA.”
“It may be justly said,” observes Halley, “that so many and so valuable
philosophical truths as are herein discovered and put past dispute
were never yet owing to the capacity and industry of any one man.”
“The importance and generality of the discoveries,” says Laplace, “and
the immense number of original and profound views, which have been the
germ of the most brilliant theories of the philosophers of this (18th)
century, and all presented with much elegance, will ensure to the work
on the _Mathematical Principles of Natural Philosophy_ a preëminence
above all the other productions of human genius.”
DESCARTES’ LABOURS IN PHYSICS.
The most profound among the many eminent thinkers France has produced,
is Réné Descartes, of whom the least that can be said is, that he
effected a revolution more decisive than has ever been brought about
by any other single mind; that he was the first who successfully
applied algebra to geometry; that he pointed out the important law of
the sines; that in an age in which optical instruments were extremely
imperfect, he discovered the changes to which light is subjected in
the eye by the crystalline lens; that he directed attention to the
consequences resulting from the weight of the atmosphere; and that he
moreover detected the causes of the rainbow. At the same time, and
as if to combine the most varied forms of excellence, he is not only
allowed to be the first geometrician of the age, but by the clearness
and admirable precision of his style, he became one of the founders
of French prose. And, although he was constantly engaged in those
lofty inquiries into the nature of the human mind, which can never
be studied without wonder, he combined with them a long course of
laborious experiment upon the animal frame, which raised him to the
highest rank among the anatomists of his time. The great discovery
made by Harvey of the Circulation of the Blood was neglected by most
of his contemporaries; but it was at once recognised by Descartes, who
made it the basis of the physiological part of his work on man. He was
likewise the discoverer of the lacteals by Aselli, which, like every
great truth yet laid before the world, was at its first appearance,
not only disbelieved, but covered with ridicule.--_Buckle’s History of
Civilization_, vol. i.
CONIC SECTIONS.
If a cone or sugar-loaf be cut through in certain directions, we shall
obtain figures which are termed conic sections: thus, if we cut through
a sugar-loaf parallel to its base or bottom, the outline or edge of the
loaf where it is cut will be _a circle_. If the cut is made so as to
slant, and not be parallel to the base of the loaf, the outline is an
_ellipse_, provided the cut goes quite through the sides of the loaf
all round; but if it goes slanting, and parallel to the line of the
loaf’s side, the outline is a _parabola_, a conic section or curve,
which is distinguished by characteristic properties, every point of it
bearing a certain fixed relation to a certain point within it, as the
circle does to its centre.--_Dr. Paris’s Notes to Philosophy in Sport,
&c._
POWER OF COMPUTATION.
The higher class of mathematicians, at the end of the seventeenth
century, had become excellent computers, particularly in England,
of which Wallis, Newton, Halley, the Gregorys, and De Moivre, are
splendid examples. Before results of extreme exactness had become
quite familiar, there was a gratifying sense of power in bringing out
the new methods. Newton, in one of his letters to Oldenburg, says
that he was at one time too much attached to such things, and that
he should be ashamed to say to what number of figures he was in the
habit of carrying his results. The growth of power of computation on
the Continent did not, however, keep pace with that of the same in
England. In 1696, De Laguy, a well-known writer on algebra, and a
member of the Academy of Sciences, said that the most skilful computer
could not, in less than a month, find within a unit the cube root of
696536483318640035073641037.--_De Morgan._
“THE SCIENCE OF THE COSMOS.”
Humboldt, characterises this “uncommon but definite expression” as the
treating of “the assemblage of all things with which space is filled,
from the remotest nebulæ to the climatic distribution of those delicate
tissues of vegetable matter which spread a variegated covering over the
surface of our rocks.” The word _cosmos_, which primitively, in the
Homeric ages, indicated an idea of order and harmony, was subsequently
adopted in scientific language, where it was gradually applied to the
order observed in the movements of the heavenly bodies; to the whole
universe; and then finally to the world in which this harmony was
reflected to us.
Physical Phenomena.
ALL THE WORLD IN MOTION.
Humboldt, in his _Cosmos_,[6] gives the following beautiful
illustrative proofs of this phenomenon:
If, for a moment, we imagine the acuteness of our senses
preternaturally heightened to the extreme limits of telescopic
vision, and bring together events separated by wide intervals of
time, the apparent repose which reigns in space will suddenly
vanish; countless stars will be seen moving in groups in various
directions; nebulæ wandering, condensing, and dissolving like
cosmical clouds; the milky way breaking up in parts, and its
veil rent asunder. In every point of the celestial vault we
shall recognise the dominion of progressive movement, as on the
surface of the earth where vegetation is constantly putting forth
its leaves and buds, and unfolding its blossoms. The celebrated
Spanish botanist, Cavanilles, first conceived the possibility of
“seeing grass grow,” by placing the horizontal micrometer wire
of a telescope, with a high magnifying power, at one time on the
point of a bamboo shoot, and at another on the rapidly unfolding
flowering stem of an American aloe; precisely as the astronomer
places the cross of wires on a culminating star. Throughout the
whole life of physical nature--in the organic as in the sidereal
world--existence, preservation, production, and development, are
alike associated with motion as their essential condition.
THE AXIS OF ROTATION.
It is remarkable as a mechanical fact, that nothing is so permanent in
nature as the Axis of Rotation of any thing which is rapidly whirled.
We have examples of this in every-day practice. The first is the
motion of _a boy’s hoop_. What keeps the hoop from falling?--It is its
rotation, which is one of the most complicated subjects in mechanics.
Another thing pertinent to this question is, _the motion of a quoit_.
Every body who ever threw a quoit knows that to make it preserve its
position as it goes through the air, it is necessary to give it a
whirling motion. It will be seen that while whirling, it preserves its
plane, whatever the position of the plane may be, and however it may
be inclined to the direction in which the quoit travels. Now, this has
greater analogy with the motion of the earth than any thing else.
Another illustration is _the motion of a spinning top_. The greatest
mathematician of the last century, the celebrated Euler, has written
a whole book on the motion of a top, and his Latin treatise _De motu
Turbinis_ is one of the most remarkable books on mechanics. The motion
of a top is a matter of the greatest importance; it is applicable
to the elucidation of some of the greatest phenomena of nature. In
all these instances there is this wonderful tendency in rotation to
preserve the axis of rotation unaltered.--_Prof. Airy’s Lect. on
Astronomy._
THE EARTH’S ANNUAL MOTION.
In conformity with the Copernican view of our system, we must learn to
look upon the sun as the comparatively motionless centre about which
the earth performs an annual elliptic orbit of the dimensions and
excentricity, and with a velocity, regulated according to a certain
assigned law; the sun occupying one of the foci of the ellipse, and
from that station quietly disseminating on all sides its light and
heat; while the earth travelling round it, and presenting itself
differently to it at different times of the year and day, passes
through the varieties of day and night, summer and winter, which we
enjoy.--_Sir John Herschel’s Outlines of Astronomy._
Laplace has shown that the length of the day has not varied the
hundredth part of a second since the observations of Hipparchus, 2000
years ago.
STABILITY OF THE OCEAN.
In submitting this question to analysis, Laplace found that the
_equilibrium of the ocean is stable if its density is less than
the mean density of the earth_, and that its equilibrium cannot be
subverted unless these two densities are equal, or that of the earth
less than that of its waters. The experiments on the attraction of
Schehallien and Mont Cenis, and those made by Cavendish, Reich, and
Baily, with balls of lead, demonstrate that the mean density of the
earth is at least _five_ times that of water, and hence the stability
of the ocean is placed beyond a doubt. As the seas, therefore, have at
one time covered continents which are now raised above their level,
we must seek for some other cause of it than any want of stability in
the equilibrium of the ocean. How beautifully does this conclusion
illustrate the language of Scripture, “Hitherto shalt thou come, but no
further”! (_Job_ xxxviii. 11.)
COMPRESSION OF BODIES.
Sir John Leslie observes, that _air compressed_ into the fiftieth
part of its volume has its elasticity fifty times augmented: if it
continued to contract at that rate, it would, from its own incumbent
weight, acquire the density of water at the depth of thirty-four
miles. But water itself would have its density doubled at the depth
of ninety-three miles, and would attain the density of quicksilver at
the depth of 362 miles. In descending, therefore, towards the centre,
through nearly 4000 miles, the condensation of ordinary substances
would surpass the utmost powers of conception. Dr. Young says, that
steel would be compressed into one-fourth, and stone into one-eighth,
of its bulk at the earth’s centre.--_Mrs. Somerville._
THE WORLD IN A NUTSHELL.
From the many proofs of the non-contact of the atoms, even in the
most solid parts of bodies; from the very great space obviously
occupied by pores--the mass having often no more solidity than a heap
of empty boxes, of which the apparently solid parts may still be as
porous in a second degree and so on; and from the great readiness
with which light passes in all directions through dense bodies, like
glass, rock-crystal, diamond, &c., it has been argued that there is so
exceedingly little of really solid matter even in the densest mass,
that _the whole world_, if the atoms could be brought into absolute
contact, _might be compressed into a nutshell_. We have as yet no means
of determining exactly what relation this idea has to truth.--_Arnott._
THE WORLD OF ATOMS.
The infinite groups of atoms flying through all time and space, in
different directions and under different laws, have interchangeably
tried and exhibited every possible mode of rencounter: sometimes
repelled from each other by concussion; and sometimes adhering to each
other from their own jagged or pointed construction, or from the casual
interstices which two or more connected atoms must produce, and which
may be just adapted to those of other figures,--as globular, oval, or
square. Hence the origin of compound and visible bodies; hence the
origin of large masses of matter; hence, eventually, the origin of the
world.--_Dr. Good’s Book of Nature._
The great Epicurus speculated on “the plastic nature” of atoms, and
attributed to this _nature_ the power they possess of arranging
themselves into symmetric forms. Modern philosophers satisfy themselves
with attraction; and reasoning from analogy, imagine that each atom has
a polar system.--_Hunt’s Poetry of Science._
MINUTE ATOMS OF THE ELEMENTS: DIVISIBILITY OF MATTER.
So minute are the parts of the elementary bodies in their ultimate
state of division, in which condition they are usually termed _atoms_,
as to elude all our powers of inspection, even when aided by the most
powerful microscopes. Who can see the particles of gold in a solution
of that metal in _aqua regia_, or those of common salt when dissolved
in water? Dr. Thomas Thomson has estimated the bulk of an ultimate
particle or atom of lead as less than 1/888492000000000th of a cubic
inch, and concludes that its weight cannot exceed the 1/310000000000th
of a grain.
This curious calculation was made by Dr. Thomson, in order to show to
what degree Matter could be divided, and still be sensible to the eye.
He dissolved a grain of nitrate of lead in 500,000 grains of water,
and passed through the solution a current of sulphuretted hydrogen;
when the whole liquid became sensibly discoloured. Now, a grain of
water may be regarded as being almost equal to a drop of that liquid,
and a drop may be easily spread out so as to cover a square inch of
surface. But under an ordinary microscope the millionth of a square
inch may be distinguished by the eye. The water, therefore, could be
divided into 500,000,000,000 parts. But the lead in a grain of nitrate
of lead weighs 0·62 of a grain; an atom of lead, accordingly, cannot
weigh more than 1/810000000000th of a grain; while the atom of sulphur,
which in combination with the lead rendered it visible, could not
weigh more than 1/2015000000000, that is, the two-billionth part of a
grain.--_Professor Low_; _Jameson’s Journal_, No. 106.
WEIGHT OF AIR.
Air can be so rarefied that the contents of a cubic foot shall not
weigh the tenth part of a grain: if a quantity that would fill a space
the hundredth part of an inch in diameter be separated from the rest,
the air will still be found there, and we may reasonably conceive that
there may be several particles present, though the weight is less than
the seventeen-hundred-millionth of a grain.
DURATION OF THE PYRAMID.
The great reason of the duration of the pyramid above all other forms
is, that it is most fitted to resist the force of gravitation. Thus the
Pyramids of Egypt are the oldest monuments in the world.
INERTIA ILLUSTRATED.
Many things of common occurrence (says Professor Tyndall) are to be
explained by reference to the quality of inactivity. We will here state
a few of them.
When a railway train is moving, if it strike against any obstacle which
arrests its motion, the passengers are thrown forward in the direction
in which the train was proceeding. Such accidents often occur on a
small scale, in attaching carriages at railway stations. The reason is,
that the passengers share the motion of the train, and, as matter, they
tend to persist in motion. When the train is suddenly checked, this
tendency exhibits itself by the falling forward referred to. In like
manner, when a train previously at rest is suddenly set in motion, the
tendency of the passengers to remain at rest evinces itself by their
falling in a direction opposed to that in which the train moves.
THE LEANING TOWER OF PISA.[7]
Sir John Leslie used to attribute the stability of this tower to
the cohesion of the mortar it is built with being sufficient to
maintain it erect, in spite of its being out of the condition required
by physics--to wit, that “in order that a column shall stand, a
perpendicular let fall from the centre of gravity must fall within the
base.” Sir John describes the Tower of Pisa to be in violation of this
principle; but, according to later authorities, the perpendicular falls
within the base.
EARLY PRESENTIMENTS OF CENTRIFUGAL FORCES.
Jacobi, in his researches on the mathematical knowledge of the
Greeks, comments on “the profound consideration of nature evinced by
Anaxagoras, in whom we read with astonishment a passage asserting that
the moon, if the centrifugal force were intermitted, would fall to the
earth like a stone from a sling.” Anaxagoras likewise applied the same
theory of “falling where the force of rotation had been intermitted”
to all the material celestial bodies. In Aristotle and Simplicius may
also be traced the idea of “the non-falling of heavenly bodies when the
rotatory force predominates over the actual falling force, or downward
attraction;” and Simplicius mentions that “water in a phial is not
spilt when the movement of rotation is more rapid than the downward
movement of the water.” This is illustrated at the present day by
rapidly whirling a pail half-filled with water without spilling a drop.
Plato had a clearer idea than Aristotle of the _attractive force_
exercised by the earth’s centre on all heavy bodies removed from
it; for he was acquainted with the acceleration of falling bodies,
although he did not correctly understand the cause. John Philoponus,
the Alexandrian, probably in the sixth century, was the first who
ascribed the movement of the heavenly bodies to a primitive impulse,
connecting with this idea that of the fall of bodies, or the tendency
of all substances, whether heavy or light, to reach the ground. The
idea conceived by Copernicus, and more clearly expressed by Kepler,
who even applied it to the ebb and flow of the ocean, received in 1666
and 1674 a new impulse from Robert Hooke; and next Newton’s theory
of gravitation presented the grand means of converting the whole of
physical astronomy into a true _mechanism of the heavens_.
The law of gravitation knows no exception; it accounts accurately for
the most complex motions of the members of our own system; nay more,
the paths of double stars, far removed from all appreciable effects
of our portion of the universe, are in perfect accordance with its
theory.[8]
HEIGHT OF FALLS.
The fancy of the Greeks delighted itself in wild visions of the height
of falls. In Hesiod’s _Theogony_ it is said, speaking of the fall
of the Titans into Tartarus, “if a brazen anvil were to fall from
heaven nine days and nine nights long, it would reach the earth on the
tenth.” This descent of the anvil in 777,600 seconds of time gives an
equivalent in distance of 309,424 geographical miles (allowance being
made, according to Galle’s calculation, for the considerable diminution
in force of attraction at planetary distances); therefore 1½ times the
distance of the moon from the earth. But, according to the _Iliad_,
Hephæstus fell down to Lemnos in one day; “when but a little breath was
still in him.”--_Note to Humboldt’s Cosmos_, vol. iii.
RATE OF THE FALL OF BODIES.
A body falls in gravity precisely 16-1/16 feet in a second, and the
velocity increases according to the squares of the time, viz.:
In ¼ (quarter of a second) a body falls 1 foot.
½ (half a second) 4 feet.
1 second 16 ”
2 ditto 64 ”
3 ditto 144 ”
The power of gravity at two miles distance from the earth is four times
less than at one mile; at three miles nine times less, and so on. It
goes on lessening, but is never destroyed.--_Notes in various Sciences._
VARIETIES OF SPEED.
A French scientific work states the ordinary rate to be:
per second.
Of a man walking 4 feet.
Of a good horse in harness 12 ”
Of a rein-deer in a sledge on the ice 26 ”
Of an English race-horse 43 ”
Of a hare 88 ”
Of a good sailing ship 19 ”
Of the wind 82 ”
Of sound 1038 ”
Of a 24-pounder cannon-ball 1300 ”
LIFTING HEAVY PERSONS.
One of the most extraordinary pages in Sir David Brewster’s _Letters
on Natural Magic_ is the experiment in which a heavy man is raised
with the greatest facility when he is lifted up the instant that his
own lungs, and those of the persons who raise him, are inflated with
air. Thus the heaviest person in the party lies down upon two chairs,
his legs being supported by the one and his back by the other. Four
persons, one at each leg, and one at each shoulder, then try to raise
him--the person to be raised giving two signals, by clapping his hands.
At the first signal, he himself and the four lifters begin to draw a
long and full breath; and when the inhalation is completed, or the
lungs filled, the second signal is given for raising the person from
the chair. To his own surprise, and that of his bearers, he rises with
the greatest facility, as if he were no heavier than a feather. Sir
David Brewster states that he has seen this inexplicable experiment
performed more than once; and he appealed for testimony to Sir Walter
Scott, who had repeatedly seen the experiment, and performed the part
both of the load and of the bearer. It was first shown in England by
Major H., who saw it performed in a large party at Venice, under the
direction of an officer of the American navy.[9]
Sir David Brewster (in a letter to _Notes and Queries_, No. 143)
further remarks, that “the inhalation of the lifters the moment the
effort is made is doubtless essential, and for this reason: when we
make a great effort, either in pulling or lifting, we always fill the
chest with air previous to the effort; and when the inhalation is
completed, we close the _rima glottidis_ to keep the air in the lungs.
The chest being thus kept expanded, the pulling or lifting muscles have
received as it were a fulcrum round which their power is exerted; and
we can thus lift the greatest weight which the muscles are capable of
doing. When the chest collapses by the escape of the air, the lifters
lose their muscular power; reinhalation of air by the liftee can
certainly add nothing to the power of the lifters, or diminish his
own weight, which is only increased by the weight of the air which he
inhales.”
“FORCE CAN NEITHER BE CREATED NOR DESTROYED.”
Professor Faraday, in his able inquiry upon “the Conservation of
Force,” maintains that to admit that force may be destructible, or can
altogether disappear, would be to admit that matter could be uncreated;
for we know matter only by its forces. From his many illustrations we
select the following:
The indestructibility of individual matter is a most important case
of the Conservation of Chemical Force. A molecule has been endowed
with powers which give rise in it to various qualities; and those
never change, either in their nature or amount. A particle of
oxygen is ever a particle of oxygen; nothing can in the least wear
it. If it enters into combination, and disappears as oxygen; if it
pass through a thousand combinations--animal, vegetable, mineral;
if it lie hid for a thousand years, and then be evolved,--it is
oxygen with the first qualities, neither more nor less. It has
all its original force, and only that; the amount of force which
it disengaged when hiding itself, has again to be employed in a
reverse direction when it is set at liberty: and if, hereafter,
we should decompose oxygen, and find it compounded of other
particles, we should only increase the strength of the proof of the
conservation of force; for we should have a right to say of these
particles, long as they have been hidden, all that we could say of
the oxygen itself.
In conclusion, he adds:
Let us not admit the destruction or creation of force without clear
and constant proof. Just as the chemist owes all the perfection
of his science to his dependence on the certainty of gravitation
applied by the balance, so may the physical philosopher expect to
find the greatest security and the utmost aid in the principle
of the conservation of force. All that we have that is good and
safe--as the steam-engine, the electric telegraph, &c.--witness to
that principle; it would require a perpetual motion, a fire without
heat, heat without a source, action without reaction, cause without
effect, or effect without cause, to displace it from its rank as a
law of nature.
NOTHING LOST IN THE MATERIAL WORLD.
“It is remarkable,” says Kobell in his _Mineral Kingdom_, “how a change
of place, a circulation as it were, is appointed for the inanimate or
naturally immovable things upon the earth; and how new conditions,
new creations, are continually developing themselves in this way. I
will not enter here into the evaporation of water, for instance from
the widely-spreading ocean; how the clouds produced by this pass over
into foreign lands and then fall again to the earth as rain, and how
this wandering water is, partly at least, carried along new journeys,
returning after various voyages to its original home: the mere
mechanical phenomena, such as the transfer of seeds by the winds or by
birds, or the decomposition of the surface of the earth by the friction
of the elements, suffice to illustrate this.”
TIME AN ELEMENT OF FORCE.
Professor Faraday observes that Time is growing up daily into
importance as an element in the exercise of Force, which he thus
strikingly illustrates:
The earth moves in its orbit of time; the crust of the earth moves
in time; light moves in time; an electro-magnet requires time for
its charge by an electric current: to inquire, therefore, whether
power, acting either at sensible or insensible distances, always
acts in _time_, is not to be metaphysical; if it acts in time and
across space, it must act by physical lines of force; and our view
of the nature of force may be affected to the extremest degree
by the conclusions which experiment and observation on time may
supply, being perhaps finally determinable only by them. To inquire
after the possible time in which gravitating, magnetic, or electric
force is exerted, is no more metaphysical than to mark the times
of the hands of a clock in their progress; or that of the temple
of Serapis, and its ascents and descents; or the periods of the
occultation of Jupiter’s satellites; or that in which the light
comes from them to the earth. Again, in some of the known cases of
the action of time something happens while _the time_ is passing
which did not happen before, and does not continue after; it is
therefore not metaphysical to expect an effect in _every_ case, or
to endeavour to discover its existence and determine its nature.
CALCULATION OF HEIGHTS AND DISTANCES.
By the assistance of a seconds watch the following interesting
calculations may be made:
If a traveller, when on a precipice or on the top of a building,
wish to ascertain the height, he should drop a stone, or any other
substance sufficiently heavy not to be impeded by the resistance of
the atmosphere; and the number of seconds which elapse before it
reaches the bottom, carefully noted on a seconds watch, will give
the height. For the stone will fall through the space of 16-1/8
feet during the first second, and will increase in rapidity as the
square of the time employed in the fall: if, therefore, 16-1/8 be
multiplied by the number of seconds the stone has taken to fall,
this product also multiplied by the same number of seconds will
give the height. Suppose the stone takes five seconds to reach the
bottom:
16-1/8 × 5 = 80-5/8 × 5 = 403-1/8, height of the precipice.
The Count Xavier de Maistre, in his _Expédition nocturne autour
de ma Chambre_, anxious to ascertain the exact height of his room
from the ground on which Turin is built, tells us he proceeded
as follows: “My heart beat quickly, and I just counted three
pulsations from the instant I dropped my slipper until I heard
the sound as it fell in the street, which, according to the
calculations made of the time taken by bodies in their accelerated
fall, and of that employed by the sonorous undulations of the
air to arrive from the street to my ear, gave the height of my
apartment as 94 feet 3 inches 1 tenth (French measure), supposing
that my heart, agitated as it was, beat 120 times in a minute.”
A person travelling may ascertain his rate of walking by the aid
of a slight string with a piece of lead at one end, and the use of
a seconds watch; the string being knotted at distances of 44 feet,
the 120th part of an English mile, and bearing the same proportion
to a mile that half a minute bears to an hour. If the traveller,
when going at his usual rate, drops the lead, and suffers the
string to slip through his hand, the number of knots which pass in
half a minute indicate the number of miles he walks in an hour.
This contrivance is similar to a _log-line_ for ascertaining a
ship’s rate at sea: the lead is enclosed in wood (whence the name
_log_), that it may float, and the divisions, which are called
_knots_, are measured for nautical miles. Thus, if ten knots are
passed in half a minute, they show that the vessel is sailing at
the rate of ten knots, or miles, an hour: a seconds watch would
here be of great service, but the half-minute sand-glass is in
general use.
The rapidity of a river may be ascertained by throwing in a light
floating substance, which, if not agitated by the wind, will move
with the same celerity as the water: the distance it floats in a
certain number of seconds will give the rapidity of the stream; and
this indicates the height of its source, the nature of its bottom,
&c.--See _Sir Howard Douglas on Bridges_. _Thomson’s Time and
Time-keepers._
SAND IN THE HOUR-GLASS.
It is a noteworthy fact, that the flow of Sand in the Hour-glass is
perfectly equable, whatever may be the quantity in the glass; that is,
the sand runs no faster when the upper half of the glass is quite full
than when it is nearly empty. It would, however, be natural enough to
conclude, that when full of sand it would be more swiftly urged through
the aperture than when the glass was only a quarter full, and near the
close of the hour.
The fact of the even flow of sand may be proved by a very simple
experiment. Provide some silver sand, dry it over or before the fire,
and pass it through a tolerably fine sieve. Then take a tube, of any
length or diameter, closed at one end, in which make a small hole, say
the eighth of an inch; stop this with a peg, and fill up the tube with
the sifted sand. Hold the tube steadily, or fix it to a wall or frame
at any height from a table; remove the peg, and permit the sand to flow
in any measure for any given time, and note the quantity. Then let the
tube be emptied, and only half or a quarter filled with sand; measure
again for a like time, and the same quantity of sand will flow: even if
you press the sand in the tube with a ruler or stick, the flow of the
sand through the hole will not be increased.
The above is explained by the fact, that when the sand is poured into
the tube, it fills it with a succession of conical heaps; and that all
the weight which the bottom of the tube sustains is only that of the
heap which _first_ falls upon it, as the succeeding heaps do not press
downward, but only against the sides or walls of the tube.
FIGURE OF THE EARTH.
By means of a purely astronomical determination, based upon the action
which the earth exerts on the motion of the moon, or, in other words,
on the inequalities in lunar longitudes and latitudes, Laplace has
shown in one single result the mean Figure of the Earth.
It is very remarkable that an astronomer, without leaving his
observatory, may, merely by comparing his observations with
mean analytical results, not only be enabled to determine with
exactness the size and degree of ellipticity of the earth, but
also its distance from the sun and moon; results that otherwise
could only be arrived at by long and arduous expeditions to the
most remote parts of both hemispheres. The moon may therefore, by
the observation of its movements, render appreciable to the higher
departments of astronomy the ellipticity of the earth, as it taught
the early astronomers the rotundity of our earth by means of its
eclipses.--_Laplace’s Expos. du Syst. du Monde._
HOW TO ASCERTAIN THE EARTH’S MAGNITUDE.
Sir John Herschel gives the following means of approximation. It
appears by observation that two points, each ten feet above the
surface, cease to be visible from each other over still water, and, in
average atmospheric circumstances, at a distance of about eight miles.
But 10 feet is the 528th part of a mile; so that half their distance,
or four miles, is to the height of each as 4 × 528, or 2112:1, and
therefore in the same proportion to four miles is the length of the
earth’s diameter. It must, therefore, be equal to 4 × 2112 = 8448, or
in round numbers, about 8000 miles, which is not very far from the
truth.
The excess is, however, about 100 miles, or 1/80th part. As
convenient numbers to remember, the reader may bear in mind, that
in our latitude there are just as many thousands of feet in a
degree of the meridian as there are days in the year (365); that,
speaking loosely, a degree is about seventy British statute miles,
and a second about 100 feet; that the equatorial circumference of
the earth is a little less than 25,000 miles (24,899), and the
ellipticity or polar flattening amounts to 1/300th part of the
diameter.--_Outlines of Astronomy._
MASS AND DENSITY OF THE EARTH.
With regard to the determination of the Mass and Density of the Earth
by direct experiment, we have, in addition to the deviations of the
pendulum produced by mountain masses, the variation of the same
instruments when placed in a mine 1200 feet in depth. The most recent
experiments were conducted by Professor Airy, in the Harton coal-pit,
near South Shields:[10] the oscillations of the pendulum at the bottom
of the pit were compared with those of a clock above; the beats of the
clock were transferred below for comparison by an electrio wire; and it
was thus determined that a pendulum vibrating seconds at the mouth of
the pit would gain 2¼ seconds per day at its bottom. The final result
of the calculations depending on this experiment, which were published
in the _Philosophical Transactions_ of 1856, gives 6·565 for the mean
density of the earth. The celebrated Cavendish experiment, by means
of which the density of the earth was determined by observing the
attraction of leaden balls on each other, has been repeated in a manner
exhibiting an astonishing amount of skill and patience by the late Mr.
F. Baily.[11] The result of these experiments, combined with those
previously made, gives as a mean result 5·441 as the earth’s density,
when compared with water; thus confirming one of Newton’s astonishing
divinations, that the mean density of the earth would be found to be
between five and six times that of water.
Humboldt is, however, of opinion that “we know only the mass of
the whole earth and its mean density by comparing it with the
open strata, which alone are accessible to us. In the interior of
the earth, where all knowledge of its chemical and mineralogical
character fails, we are limited to as pure conjecture as in the
remotest bodies that revolve round the sun. We can determine
nothing with certainty regarding the depth at which the geological
strata must be supposed to be in a state of softening or of liquid
fusion, of the condition of fluids when heated under an enormous
pressure, or of the law of the increase of density from the upper
surface to the centre of the earth.”--_Cosmos_, vol. i.
In M. Foucault’s beautiful experiment, by means of the vibration of
a long pendulum, consisting of a heavy mass of metal suspended by a
long wire from a strong fixed support, is demonstrated to the eye
the rotation of the earth. The Gyroscope of the same philosopher
is regarded not as a mere philosophical toy; but the principles of
dynamics, by means of which it is made to demonstrate the earth’s
rotation on its own axis, are explained with the greatest clearness.
Thus the ingenuity of M. Foucault, combined with a profound knowledge
of mechanics, has obtained proofs of one of the most interesting
problems of astronomy from an unsuspected source.
THE EARTH AND MAN COMPARED.
The Earth--speaking roundly--is 8000 miles in diameter; the atmosphere
is calculated to be fifty miles in altitude; the loftiest mountain peak
is estimated at five miles above the level of the sea, for this height
has never been visited by man; the deepest mine that he has formed is
1650 feet; and his own stature does not average six feet. Therefore, if
it were possible for him to construct a globe 800 feet--or twice the
height of St. Paul’s Cathedral--in diameter, and to place upon any one
point of its surface an atom of 1/4380th of an inch in diameter, and
1/720th of an inch in height, it would correctly denote the proportion
that man bears to the earth upon which he moves.
When by measurements, in which the evidence of the method advances
equally with the precision of the results, the volume of the earth
is reduced to the millionth part of the volume of the sun; when
the sun himself, transported to the region of the stars, takes
up a very modest place among the thousands of millions of those
bodies that the telescope has revealed to us; when the 38,000,000
of leagues which separate the earth from the sun have become, by
reason of their comparative smallness, a base totally insufficient
for ascertaining the dimensions of the visible universe; when even
the swiftness of the luminous rays (77,000 leagues per second)
barely suffices for the common valuations of science; when, in
short, by a chain of irresistible proofs, certain stars have
retired to distances that light could not traverse in less than a
million of years;--we feel as if annihilated by such immensities.
In assigning to man and to the planet that he inhabits so small a
position in the material world, astronomy seems really to have made
progress only to humble us.--_Arago._
MEAN TEMPERATURE OF THE EARTH’S SURFACE.
Professor Dove has shown, by taking at all seasons the mean of the
temperature of points diametrically opposite to each other, that the
mean temperature _of the whole earth’s surface_ in June considerably
exceeds that in December. This result, which is at variance with the
greater proximity of the sun in December, is, however, due to a totally
different and very powerful cause,--the greater amount of land in
that hemisphere which has its summer solstice in June (_i. e._ the
northern); and the fact is so explained by him. The effect of land
under sunshine is to throw heat into the general atmosphere, and to
distribute it by the carrying power of the latter over the whole earth.
Water is much less effective in this respect, the heat penetrating its
depths and being there absorbed; so that the surface never acquires
a very elevated temperature, even under the equator.--_Sir John
Herschel’s Outlines._
TEMPERATURE OF THE EARTH STATIONARY.
Although, according to Bessel, 25,000 cubic miles of water flow in
every six hours from one quarter of the earth to another, and the
temperature is augmented by the ebb and flow of every tide, all
that we know with certainty is, that the _resultant effect_ of all
the thermal agencies to which the earth is exposed has undergone
no perceptible change within the historic period. We owe this fine
deduction to Arago. In order that the _date palm_ should ripen its
fruit, the mean temperature of the place must exceed 70 deg. Fahr.;
and, on the other hand, the _vine_ cannot be cultivated successfully
when the temperature is 72 deg. or upwards. Hence the mean temperature
of any place at which these two plants flourished and bore fruit must
lie between these narrow limits, _i. e._ could not differ from 71 deg.
Fahr. by more than a single degree. Now from the Bible we learn that
both plants were _simultaneously_ cultivated in the central valleys
of Palestine in the time of Moses; and its then temperature is thus
definitively determined. It is the same at the present time; so that
the mean temperature of this portion of the globe has not sensibly
altered in the course of thirty-three centuries.
THEORY OF CRYSTALLISATION.
Professor Plücker has ascertained that certain crystals, in particular
the cyanite, “point very well to the north by the magnetic power of the
earth only. It is a true compass-needle; and more than that, you may
obtain its declination.” Upon this Mr. Hunt remarks: “We must remember
that this crystal, the cyanite, is a compound of silica and alumina
only. This is the amount of experimental evidence which science has
afforded in explanation of the conditions under which nature pursues
her wondrous work of crystal formation. We see just sufficient of
the operation to be convinced that the luminous star which shines in
the brightness of heaven, and the cavern-secreted gem, are equally
the result of forces which are known to us in only a few of their
modifications.”--_Poetry of Science._
Gay Lussac first made the remark, that a crystal of potash-alum,
transferred to a solution of ammonia-alum, continued to increase
without its form being modified, and might thus be covered with
alternate layers of the two alums, preserving its regularity and proper
crystalline figure. M. Beudant afterwards observed that other bodies,
such as the sulphates of iron and copper, might present themselves
in crystals of the same form and angles, although the form was not a
simple one, like that of alum. But M. Mitscherlich first recognised
this correspondence in a sufficient number of cases to prove that it
was a general consequence of similarity of composition in different
bodies.--_Graham’s Elements of Chemistry._
IMMENSE CRYSTALS.
Crystals are found in the most microscopic character, and of an
exceedingly large size. A crystal of quartz at Milan is three feet and
a quarter long, and five feet and a half in circumference: its weight
is 870 pounds. Beryls have been found in New Hampshire measuring four
feet in length.--_Dana._
VISIBLE CRYSTALLISATION.
Professor Tyndall, in a lecture delivered by him at the Royal
Institution, London, on the properties of Ice, gave the following
interesting illustration of crystalline force. By perfectly cleaning a
piece of glass, and placing on it a film of a solution of chloride of
ammonium or sal ammoniac, the action of crystallisation was shown to
the whole audience. The glass slide was placed in a microscope, and the
electric light passing through it was concentrated on a white disc. The
image of the crystals, as they started into existence, and shot across
the disc in exquisite arborescent and symmetrical forms, excited the
admiration of every one. The lecturer explained that the heat, causing
the film of moisture to evaporate, brought the particles of salt
sufficiently near to exercise the crystalline force, the result being
the beautiful structure built up with such marvellous rapidity.
UNION OF MINERALOGY AND GEOMETRY.
It is a peculiar characteristic of minerals, that while plants and
animals differ in various regions of the earth, mineral matter of the
same character may be discovered in any part of the world,--at the
Equator or towards the Poles; at the summit of the loftiest mountains,
and in works far beneath the level of the sea. The granite of Australia
does not necessarily differ from that of the British islands; and ores
of the same metals (the proper geological conditions prevailing) may
be found of the same general character in all regions. Climate and
geographical position have no influence on the composition of mineral
substances.
This uniformity may, in some measure, have induced philosophers to
seek its extension to the forms of crystallography. About 1760 (says
Mr. Buckle, in his _History of Civilization_), Romé de Lisle set the
first example of studying crystals, according to a scheme so large as
to include all the varieties of their primary forms, and to account
for their irregularities and the apparent caprice with which they
were arranged. In this investigation he was guided by the fundamental
assumption, that what is called an irregularity is in truth perfectly
regular, and that the operations of nature are invariable. Haüy applied
this great idea to the almost innumerable forms in which minerals
crystallise. He thus achieved a complete union between mineralogy and
geometry; and, bringing the laws of space to bear on the molecular
arrangements of matter, he was able to penetrate into the intimate
structure of crystals. By this means he proved that the secondary
forms of all crystals are derived from their primary forms by a
regular process of decrement; and that when a substance is passing
from a liquid to a solid state, its particles cohere, according to a
scheme which provides for every possible change, since it includes
even those subsequent layers which alter the ordinary type of the
crystal, by disturbing its natural symmetry. To ascertain that such
violations of symmetry are susceptible of mathematical calculation,
was to make a vast addition to our knowledge; and, by proving that
even the most uncouth and singular forms are the natural results of
their antecedents, Haüy laid the foundation of what may be called the
pathology of the inorganic world. However paradoxical such a notion may
appear, it is certain that symmetry is to crystals what health is to
animals; so that an irregularity of shape in the first corresponds with
an appearance of disease in the second.--See _Hist. Civilization_, vol.
i.
REPRODUCTIVE CRYSTALLISATION.
The general belief that only organic beings have the power of
reproducing lost parts has been disproved by the experiments of Jordan
on crystals. An octohedral crystal of alum was fractured; it was then
replaced in a solution, and after a few days its injury was seen to be
repaired. The whole crystal had of course increased in size; but the
increase on the broken surface had been so much greater that a perfect
octohedral form was regained.--_G. H. Lewes._
This remarkable power possessed by crystals, in common with animals,
of repairing their own injuries had, however, been thus previously
referred to by Paget, in his _Pathology_, confirming the experiments
of Jordan on this curious subject: “The ability to repair the damages
sustained by injury ... is not an exclusive property of living beings;
for even crystals will repair themselves when, after pieces have been
broken from them, they are placed in the same conditions in which they
were first formed.”
GLASS BROKEN BY SAND.
In some glass-houses the workmen show glass which has been cooled in
the open air; on this they let fall leaden bullets without breaking the
glass. They afterwards desire you to let a few grains of sand fall upon
the glass, by which it is broken into a thousand pieces. The reason
of this is, that the lead does not scratch the surface of the glass;
whereas the sand, being sharp and angular, scratches it sufficiently to
produce the above effect.
Sound and Light.
SOUNDING SAND.
Mr. Hugh Miller, the geologist, when in the island of Eigg, in the
Hebrides, observed that a musical sound was produced when he walked
over the white dry sand of the beach. At each step the sand was driven
from his footprint, and the noise was simultaneous with the scattering
of the sand; the cause being either the accumulated vibrations of
the air when struck by the driven sand, or the accumulated sounds
occasioned by the mutual impact of the particles of sand against each
other. If a musket-ball passing through the air emits a whistling note,
each individual particle of sand must do the same, however faint be
the note which it yields; and the accumulation of these infinitesimal
vibrations must constitute an audible sound, varying with the number
and velocity of the moving particles. In like manner, if two plates of
silex or quartz, which are but crystals of sand, give out a musical
sound when mutually struck, the impact or collision of two minute
crystals or particles of sand must do the same, in however inferior a
degree; and the union of all these sounds, though singly imperceptible,
may constitute the musical notes of “the Mountain of the Bell” in
Arabia Petræa, or the lesser sounds of the trodden sea-beach of
Eigg.--_North-British Review_, No. 5.
INTENSITY OF SOUND IN RAREFIED AIR.
The experiences during ascents of the highest mountains are
contradictory. Saussure describes the sounds on the top of Mont Blanc
as remarkably weak: a pistol-shot made no more noise than an ordinary
Chinese cracker, and the popping of a bottle of champagne was scarcely
audible. Yet Martius, in the same situation, was able to distinguish
the voices of the guides at a distance of 1340 feet, and to hear the
tapping of a lead pencil upon a metallic surface at a distance of from
75 to 100 feet.
MM Wertheim and Breguet have propagated sound over the wire of an
electric telegraph at the rate of 11,454 feet per second.
DISTANCE AT WHICH THE HUMAN VOICE MAY BE HEARD.
Experience shows that the human voice, under favourable circumstances,
is capable of filling a larger space than was ever probably enclosed
within the walls of a single room. Lieutenant Foster, on Parry’s third
Arctic expedition, found that he could converse with a man across the
harbour of Port Bowen, a distance of 6696 feet, or about one mile and a
quarter. Dr. Young records that at Gibraltar the human voice has been
heard at a distance of ten miles. If sound be prevented from spreading
and losing itself in the air, either by a pipe or an extensive flat
surface, as a wall or still water, it may be conveyed to a great
distance. Biot heard a flute clearly through a tube of cast-iron (the
water-pipes of Paris) 3120 feet long: the lowest whisper was distinctly
heard; indeed, the only way not to be heard was not to speak at all.
THE ROAR OF NIAGARA.
The very nature of the sound of running water pronounces its origin
to be the bursting of bubbles: the impact of water against water is a
comparatively subordinate cause, and could never of itself occasion the
murmur of a brook; whereas, in streams which Dr. Tyndall has examined,
he, in all cases where a ripple was heard, discovered bubbles caused by
the broken column of water. Now, were Niagara continuous, and without
lateral vibration, it would be as silent as a cataract of ice. In all
probability, it has its “contracted sections,” after passing which
it is broken into detached masses, which, plunging successively upon
the air-bladders formed by their precursors, suddenly liberate their
contents, and thus create _the thunder of the waterfall_.
FIGURES PRODUCED BY SOUND.
Stretch a sheet of wet paper over the mouth of a glass tumbler which
has a footstalk, and glue or paste the paper at the edges. When the
paper is dry, strew dry sand thinly upon its surface. Place the tumbler
on a table, and hold immediately above it, and parallel to the paper,
a plate of glass, which you also strew with sand, having previously
rubbed the edges smooth with emery powder. Draw a violin-bow along any
part of the edges; and as the sand upon the glass is made to vibrate,
it will form various figures, which will be accurately imitated by the
sand upon the paper; or if a violin or flute be played within a few
inches of the paper, they will cause the sand upon its surface to form
regular lines and figures.
THE TUNING-FORK A FLUTE-PLAYER.
Take a common tuning-fork, and on one of its branches fasten with
sealing-wax a circular piece of card of the size of a small wafer, or
sufficient nearly to cover the aperture of a pipe, as the sliding of
the upper end of a flute with the mouth stopped: it may be tuned in
unison with the loaded tuning-fork by means of the movable stopper or
card, or the fork may be loaded till the unison is perfect. Then set
the fork in vibration by a blow on the unloaded branch, and hold the
card closely over the mouth of the pipe, as in the engraving, when a
note of surprising clearness and strength will be heard. Indeed a flute
may be made to “speak” perfectly well, by holding close to the opening
a vibrating tuning-fork, while the fingering proper to the note of the
fork is at the same time performed.
THEORY OF THE JEW’S HARP.
If you cause the tongue of this little instrument to vibrate, it will
produce a very low sound; but if you place it before a cavity (as the
mouth) containing a column of air, which vibrates much faster, but
in the proportion of any simple multiple, it will then produce other
higher sounds, dependent upon the reciprocation of that portion of
the air. Now the bulk of air in the mouth can be altered in its form,
size, and other circumstances, so as to produce by reciprocation many
different sounds; and these are the sounds belonging to the Jew’s Harp.
A proof of this fact has been given by Mr. Eulenstein, who fitted into
a long metallic tube a piston, which being moved, could be made to
lengthen or shorten the efficient column of air within at pleasure. A
Jew’s Harp was then so fixed that it could be made to vibrate before
the mouth of the tube, and it was found that the column of air produced
a series of sounds, according as it was lengthened or shortened; a
sound being produced whenever the length of the column was such that
its vibrations were a multiple of those of the Jew’s Harp.
SOLAR AND ARTIFICIAL LIGHT COMPARED.
The most intensely ignited solid (produced by the flame of Lieutenant
Drummond’s oxy-hydrogen lamp directed against a surface of chalk)
appears only as black spots on the disc of the sun, when held between
it and the eye; or in other words, Drummond’s light is to the light of
the sun’s disc as 1 to 146. Hence we are doubly struck by the felicity
with which Galileo, as early as 1612, by a series of conclusions on
the smallness of the distance from the sun at which the disc of Venus
was no longer visible to the naked eye, arrived at the result that
the blackest nucleus of the sun’s spots was more luminous than the
brightest portions of the full moon. (See “The Sun’s Light compared
with Terrestrial Lights,” in _Things not generally Known_, pp. 4, 5.)
SOURCE OF LIGHT.
Mr. Robert Hunt, in a lecture delivered by him at the Russell
Institution, “On the Physics of a Sunbeam,” mentions some experiments
by Lord Brougham on the sunbeam, in which, by placing the edge of a
sharp knife just within the limit of the light, the ray was inflected
from its previous direction, and coloured red; and when another knife
was placed on the opposite side, it was deflected, and the colour was
blue. These experiments (says Mr. Hunt) seem to confirm Sir Isaac
Newton’s theory, that light is a fluid emitted from the sun.
THE UNDULATORY SCALE OF LIGHT.
The white light of the sun is well known to be composed of several
coloured rays; or rather, according to the theory of undulations, when
the rate at which a ray vibrates is altered, a different sensation
is produced upon the optic nerve. The analytical examination of
this question shows that to produce a red colour the ray of light
must give 37,640 undulations in an inch, and 458,000,000,000,000 in
a second. Yellow light requires 44,000 undulations in an inch, and
535,000,000,000,000 in a second; whilst the effect of blue results from
51,110 undulations within an inch, and 622,000,000,000,000 of waves in
a second of time.--_Hunt’s Poetry of Science._
VISIBILITY OF OBJECTS.
In terrestrial objects, the form, no less than the modes of
illumination, determines the magnitude of the smallest angle of vision
for the naked eye. Adams very correctly observed that a long and
slender staff can be seen at a much greater distance than a square
whose sides are equal to the diameter of the staff. A stripe may be
distinguished at a greater distance than a spot, even when both are of
the same diameter.
The _minimum_ optical visual angle at which terrestrial objects can
be recognised by the naked eye has been gradually estimated lower and
lower, from the time when Robert Hooke fixed it exactly at a full
minute, and Tobias Meyer required 34″ to perceive a black speck on
white paper, to the period of Leuwenhoeck’s experiments with spiders’
threads, which are visible to ordinary sight at an angle of 4″·7. In
Hueck’s most accurate experiments on the problem of the movement of
the crystalline lens, white lines on a black ground were seen at an
angle of 1″·2; a spider’s thread at 0″·6; and a fine glistening wire at
scarcely 0″·2.
Humboldt, when at Chillo, near Quito, where the crests of the
volcano of Pichincha lay at a horizontal distance of 90,000 feet,
was much struck by the circumstance that the Indians standing near
distinguished the figure of Bonpland (then on an expedition to the
volcano), as a white point moving on the black basaltic sides of
the rock, sooner than Humboldt could discover him with a telescope.
Bonpland was enveloped in a white cotton poncho: assuming the
breadth across the shoulders to vary from three to five feet,
according as the mantle clung to the figure or fluttered in the
breeze, and judging from the known distance, the angle at which the
moving object could be distinctly seen varied from 7″ to 12″. White
objects on a black ground are, according to Hueck, distinguished at
a greater distance than black objects on a white ground.
Gauss’s heliotrope light has been seen with the naked eye reflected
from the Brocken on Hobenhagen at a distance of about 227,000 feet,
or more than 42 miles; being frequently visible at points in which
the apparent breadth of a three-inch mirror was only 0″·43.
THE SMALLEST BRIGHT BODIES.
Ehrenberg has found from experiments on the dust of diamonds, that
a diamond superficies of 1/100th of a line in diameter presents a
much more vivid light to the naked eye than one of quicksilver of the
same diameter. On pressing small globules of quicksilver on a glass
micrometer, he easily obtained smaller globules of the 1/100th to the
1/2000th of a line in diameter. In the sunshine he could only discern
the reflection of light, and the existence of such globules as were
1/300th of a line in diameter, with the naked eye. Smaller ones did
not affect his eye; but he remarked that the actual bright part of the
globule did not amount to more than 1/900th of a line in diameter.
Spider threads of 1/2000th in diameter were still discernible from
their lustre. Ehrenberg concludes that there are in organic bodies
magnitudes capable of direct proof which are in diameter 1/100000 of a
line; and others, that can be indirectly proved, which may be less than
a six-millionth part of a Parisian line in diameter.
VELOCITY OF LIGHT.
It is scarcely possible so to strain the imagination as to conceive
the Velocity with which Light travels. “What mere assertion will make
any man believe,” asks Sir John Herschel, “that in one second of time,
in one beat of the pendulum of a clock, a ray of light travels over
192,000 miles; and would therefore perform the tour of the world in
about the same time that it requires to wink with our eyelids, and in
much less time than a swift runner occupies in taking a single stride?”
Were a cannon-ball shot directly towards the sun, and were it to
maintain its full speed, it would be twenty years in reaching it; and
yet light travels through this space in seven or eight minutes.
The result given in the _Annuaire_ for 1842 for the velocity of light
in a second is 77,000 leagues, which corresponds to 215,834 miles;
while that obtained at the Pulkowa Observatory is 189,746 miles.
William Richardson gives as the result of the passage of light from the
sun to the earth 8´ 19″·28, from which we obtain a velocity of 215,392
miles in a second.--_Memoirs of the Astronomical Society_, vol. iv.
In other words, light travels a distance equal to eight times the
circumference of the earth between two beats of a clock. This is a
prodigious velocity; but the measure of it is very certain.--_Professor
Airy._
The navigator who has measured the earth’s circuit by his hourly
progress, or the astronomer who has paced a degree of the meridian, can
alone form a clear idea of velocity, when we tell him that light moves
through a space equal to the circumference of the earth in _the eighth
part of a second_--in the twinkling of an eye.
Could an observer, placed in the centre of the earth, see this
moving light, as it describes the earth’s circumference, it would
appear a luminous ring; that is, the impression of the light at the
commencement of its journey would continue on the retina till the
light had completed its circuit. Nay, since the impression of light
continues longer than the _fourth_ part of a second, _two_ luminous
rings would be seen, provided the light made _two_ rounds of the
earth, and in paths not coincident.
APPARATUS FOR THE MEASUREMENT OF LIGHT.
Humboldt enumerates the following different methods adopted for the
Measurement of Light: a comparison of the shadows of artificial lights,
differing in numbers and distance; diaphragms; plane-glasses of
different thickness and colour; artificial stars formed by reflection
on glass spheres; the juxtaposition of two seven-feet telescopes,
separated by a distance which the observer could pass in about a
second; reflecting instruments in which two stars can be simultaneously
seen and compared, when the telescope has been so adjusted that the
star gives two images of like intensity; an apparatus having (in
front of the object-glass) a mirror and diaphragms, whose rotation
is measured on a ring; telescopes with divided object-glasses, on
either half of which the stellar light is received through a prism;
astrometers, in which a prism reflects the image of the moon or
Jupiter, and concentrates it through a lens at different distances into
a star more or less bright.--_Cosmos_, vol. iii.
HOW FIZEAU MEASURED THE VELOCITY OF LIGHT.
This distinguished physicist has submitted the Velocity of Light
to terrestrial measurement by means of an ingeniously constructed
apparatus, in which artificial light (resembling stellar light),
generated from oxygen and hydrogen, is made to pass back, by means of
a mirror, over a distance of 28,321 feet to the same point from which
it emanated. A disc, having 720 teeth, which made 12·6 rotations in a
second, alternately obscured the ray of light and allowed it to be seen
between the teeth on the margin. It was supposed, from the marking of
a counter, that the artificial light traversed 56,642 feet, or the
distance to and from the stations, in 1/1800th part of a second, whence
we obtain a velocity of 191,460 miles in a second.[12] This result
approximates most closely to Delambre’s (which was 189,173 miles), as
obtained from Jupiter’s satellites.
The invention of the rotating mirror is due to Wheatstone, who made
an experiment with it to determine the velocity of the propagation
of the discharge of a Leyden battery. The most striking application
of the idea was made by Fizeau and Foucault, in 1853, in carrying
out a proposition made by Arago, soon after the invention of the
mirror: we have here determined in a distance of twelve feet no
less than the velocity with which light is propagated, which is
known to be nearly 200,000 miles a second; the distance mentioned
corresponds therefore to the 77-millionth part of a second. The
object of these measurements was to compare the velocity of light
in air with its velocity in water; which, when the length is
greater, is not sufficiently transparent. The most complete optical
and mechanical aids are here necessary: the mirror of Foucault
made from 600 to 800 revolutions in a second, while that of Fizeau
performed 1200 to 1500 in the same time.--_Prof. Helmholtz on the
Methods of Measuring very small Portions of Time._
WHAT IS DONE BY POLARISATION OF LIGHT.
Malus, in 1808, was led by a casual observation of the light of the
setting sun, reflected from the windows of the Palais de Luxembourg,
at Paris, to investigate more thoroughly the phenomena of double
refraction, of ordinary and of chromatic polarisation, of interference
and of diffraction of light. Among his results may be reckoned the
means of distinguishing between direct and reflected light; the power
of penetrating, as it were, into the constitution of the body of
the sun and of its luminous envelopes; of measuring the pressure of
atmospheric strata, and even the smallest amount of water they contain;
of ascertaining the depths of the ocean and its rocks by means of
a tourmaline plate; and in accordance with Newton’s prediction, of
comparing the chemical composition of several substances with their
optical effects.
Arago, in a letter to Humboldt, states that by the aid of his
polariscope, he discovered, before 1820, that the light of all
terrestrial objects in a state of incandescence, whether they be
solid or liquid, is natural, so long as it emanates from the object
in perpendicular rays. On the other hand, if such light emanate
at an acute angle, it presents manifest proofs of polarisation.
This led M. Arago to the remarkable conclusion, that light is not
generated on the surface of bodies only, but that some portion is
actually engendered within the substance itself, even in the case
of platinum.
A ray of light which reaches our eyes after traversing many millions
of miles, from, the remotest regions of heaven, announces, as it were
of itself, in the polariscope, whether it is reflected or refracted,
whether it emanates from a solid or fluid or gaseous body; it announces
even the degree of its intensity.--_Humboldt’s Cosmos_, vols. i. and ii.
MINUTENESS OF LIGHT.
There is something wonderful, says Arago, in the experiments which have
led natural philosophers legitimately to talk of the different sides of
a ray of light; and to show that millions and millions of these rays
can simultaneously pass through the eye of a needle without interfering
with each other!
THE IMPORTANCE OF LIGHT.
Light affects the respiration of animals just as it affects the
respiration of plants. This is novel doctrine, but it is demonstrable.
In the day-time we expire more carbonic acid than during the night; a
fact known to physiologists, who explain it as the effect of sleep: but
the difference is mainly owing to the presence or absence of sunlight;
for sleep, as sleep, _increases_, instead of diminishing, the amount
of carbonic acid expired, and a man sleeping will expire more carbonic
acid than if he lies quietly awake under the same conditions of light
and temperature; so that if less is expired during the night than
during the day, the reason cannot be sleep, but the absence of light.
Now we understand why men are sickly and stunted who live in narrow
streets, alleys, and cellars, compared with those who, under similar
conditions of poverty and dirt, live in the sunlight.--_Blackwood’s
Edinburgh Magazine_, 1858.
The influence of light on the colours of organised creation is well
shown in the sea. Near the shores we find seaweeds of the most
beautiful hues, particularly on the rocks which are left dry by
the tides; and the rich tints of the actiniæ which inhabit shallow
water must often have been observed. The fishes which swim near the
surface are also distinguished by the variety of their colours,
whereas those which live at greater depths are gray, brown, or
black. It has been found that after a certain depth, where the
quantity of light is so reduced that a mere twilight prevails, the
inhabitants of the ocean become nearly colourless.--_Hunt’s Poetry
of Science._
ACTION OF LIGHT ON MUSCULAR FIBRES.
That light is capable of acting on muscular fibres, independently
of the influence of the nerves, was mentioned by several of the old
anatomists, but repudiated by later authorities. M. Brown Séquard has,
however, proved to the Royal Society that some portions of muscular
fibre--the iris of the eye, for example--are affected by light
independently of any reflex action of the nerves, thereby confirming
former experiences. The effect is produced by the illuminating rays
only, the chemical and heat rays remaining neutral. And not least
remarkable is the fact, that the iris of an eel showed itself
susceptible of the excitement _sixteen days after the eyes were removed
from the creature’s head_. So far as is yet known, this muscle is the
only one on which light thus takes effect.--_Phil. Trans. 1857._
LIGHT NIGHTS.
It is not possible, as well-attested facts prove, perfectly to explain
the operations at work in the much-contested upper boundaries of
our atmosphere. The extraordinary lightness of whole nights in the
year 1831, during which small print might be read at midnight in
the latitudes of Italy and the north of Germany, is a fact directly
at variance with all that we know, according to the most recent and
acute researches on the crepuscular theory and the height of the
atmosphere.--_Biot._
PHOSPHORESCENCE OF PLANTS.
Mr. Hunt recounts these striking instances. The leaves of the _œnothera
macrocarpa_ are said to exhibit phosphoric light when the air is
highly charged with electricity. The agarics of the olive-grounds of
Montpelier too have been observed to be luminous at night; but they
are said to exhibit no light, even in darkness, _during the day_. The
subterranean passages of the coal-mines near Dresden are illuminated by
the phosphorescent light of the _rhizomorpha phosphoreus_, a peculiar
fungus. On the leaves of the Pindoba palm grows a species of agaric
which is exceedingly luminous at night; and many varieties of the
lichens, creeping along the roofs of caverns, lend to them an air of
enchantment by the soft and clear light which they diffuse. In a small
cave near Penryn, a luminous moss is abundant; it is also found in the
mines of Hesse. According to Heinzmann, the _rhizomorpha subterranea_
and _aidulæ_ are also phosphorescent.--See _Poetry of Science_.
PHOSPHORESCENCE OF THE SEA.
By microscopic examination of the myriads of minute insects which cause
this phenomenon, no other fact has been elicited than that they contain
a fluid which, when squeezed out, leaves a train of light upon the
surface of the water. The creatures appear almost invariably on the eve
of some change of weather, which would lead us to suppose that their
luminous phenomena must be connected with electrical excitation; and of
this Mr. C. Peach of Fowey has furnished the most satisfactory proofs
yet obtained.[13]
LIGHT FROM THE JUICE OF A PLANT.
In Brazil has been observed a plant, conjectured to be an Euphorbium,
very remarkable for the light which it yields when cut. It contains a
milky juice, which exudes as soon as the plant is wounded, and appears
luminous for several seconds.
LIGHT FROM FUNGUS.
Phosphorescent funguses have been found in Brazil by Mr. Gardner,
growing on the decaying leaves of a dwarf palm. They vary from one to
two inches across, and the whole plant gives out at night a bright
phosphorescent light, of a pale greenish hue, similar to that emitted
by fire-flies and phosphorescent marine animals. The light given out by
a few of these fungi in a dark room is sufficient to read by. A very
large phosphorescent species is occasionally found in the Swan River
colony.
LIGHT FROM BUTTONS.
Upon highly polished gilt buttons no figure whatever can be seen by the
most careful examination; yet, when they are made to reflect the light
of the sun or of a candle upon a piece of paper held close to them,
they give a beautiful geometrical figure, with ten rays issuing from
the centre, and terminating in a luminous rim.
COLOURS OF SCRATCHES.
An extremely fine scratch on a well-polished surface may be regarded as
having a concave, cylindrical, or at least a curved surface, capable of
reflecting light in all directions; this is evident, for it is visible
in all directions. Hence a single scratch or furrow in a surface may
produce colours by the interference of the rays reflected from its
opposite edges. Examine a spider’s thread in the sunshine, and it will
gleam with vivid colours. These may arise from a similar cause; or from
the thread itself, as spun by the animal, consisting of several threads
agglutinated together, and thus presenting, not a cylindrical, but a
furrowed surface.
MAGIC BUST.
Sir David Brewster has shown how the rigid features of a white bust
may be made to move and vary their expression, sometimes smiling and
sometimes frowning, by moving rapidly in front of the bust a bright
light, so as to make the lights and shadows take every possible
direction and various degrees of intensity; and if the bust be placed
before a concave mirror, its image may be made to do still more when it
is cast upon wreaths of smoke.
COLOURS HIT MOST FREQUENTLY DURING BATTLE.
It would appear from numerous observations that soldiers are hit
during battle according to the colour of their dress in the following
order: red is the most fatal colour; the least fatal, Austrian gray.
The proportions are, red, 12; rifle-green, 7; brown, 6; Austrian
bluish-gray, 5.--_Jameson’s Journal_, 1853.
TRANSMUTATION OF TOPAZ.
Yellow topazes may be converted into pink by heat; but it is a mistake
to suppose that in the process the yellow colour is changed into pink:
the fact is, that one of the pencils being yellow and the other pink,
the yellow is discharged by heat, thus leaving the pink unimpaired.
COLOURS AND TINTS.
M. Chevreul, the _Directeur des Gobelins_, has presented to the French
Academy a plan for a universal chromatic scale, and a methodical
classification of all imaginable colours. Mayer, a professor at
Göttingen, calculated that the different combinations of primitive
colours produced 819 different tints; but M. Chevreul established not
less than 14,424, all very distinct and easily recognised,--all of
course proceeding from the three primitive simple colours of the solar
spectrum, red, yellow, and blue. For example, he states that in the
violet there are twenty-eight colours, and in the dahlia forty-two.
OBJECTS REALLY OF NO COLOUR.
A body appears to be of the colour which it reflects; as we see it only
by reflected rays, it can but appear of the colour of those rays. Thus
grass is green because it absorbs all except the green rays. Flowers,
in the same manner, reflect the various colours of which they appear
to us: the rose, the red rays; the violet, the blue; the daffodil,
the yellow, &c. But these are not the permanent colours of the grass
and flowers; for wherever you see these colours, the objects must be
illuminated; and light, from whatever source it proceeds, is of the
same nature, composed of the various coloured rays which paint the
grass, the flowers, and every coloured object in nature. Objects in
the dark have no colour, or are black, which is the same thing. You
can never see objects without light. Light is composed of colours,
therefore there can be no light without colours; and though every
object is black or without colour in the dark, it becomes coloured as
soon as it becomes visible.
THE DIORAMA--WHY SO PERFECT AN ILLUSION.
Because when an object is viewed at so great a distance that the
optic axes of both eyes are sensibly parallel when directed towards
it, the perspective projections of it, seen by each eye separately,
are similar; and the appearance to the two eyes is precisely the same
as when the object is seen by one eye only. There is, in such case,
no difference between the visual appearance of an object in relief
and its perspective projection on a plane surface; hence pictorial
representations of distant objects, when those circumstances which
would prevent or disturb the illusion are carefully excluded, may be
rendered such perfect resemblances of the objects they are intended to
represent as to be mistaken for them. The Diorama is an instance of
this.--_Professor Wheatstone_; _Philosophical Transactions_, 1838.
CURIOUS OPTICAL EFFECTS AT THE CAPE.
Sir John Herschel, in his observatory at Feldhausen, at the base of
the Table Mountain, witnessed several curious optical effects, arising
from peculiar conditions of the atmosphere incident to the climate of
the Cape. In the hot season “the nights are for the most part superb;”
but occasionally, during the excessive heat and dryness of the sandy
plains, “the optical tranquillity of the air” is greatly disturbed.
In some cases, the images of the stars are violently dilated into
nebular balls or puffs of 15′ in diameter; on other occasions they
form “soft, round, quiet pellets of 3′ or 4′ diameter,” resembling
planetary nebulæ. In the cooler months the tranquillity of the image
and the sharpness of vision are such, that hardly any limit is set
to magnifying power but that which arises from the aberration of the
specula. On occasions like these, optical phenomena of extraordinary
splendour are produced by viewing a bright star through a diaphragm
of cardboard or zinc pierced in regular patterns of circular holes by
machinery: these phenomena surprise and delight every person that sees
them. When close double stars are viewed with the telescope, with a
diaphragm in the form of an equilateral triangle, the discs of the two
stars, which are exact circles, have a clearness and perfection almost
incredible.
THE TELESCOPE AND THE MICROSCOPE.
So singular is the position of the Telescope and the Microscope among
the great inventions of the age, that no other process but that which
they embody could make the slightest approximation to the secrets which
they disclose. The steam-engine might have been imperfectly replaced
by an air or an ether-engine; and a highly elastic fluid might have
been, and may yet be, found, which shall impel the “rapid car,” or
drag the merchant-ship over the globe. The electric telegraph, now so
perfect and unerring, might have spoken to us in the rude “language
of chimes;” or sound, in place of electricity, might have passed along
the metallic path, and appealed to the ear in place of the eye. For
the printing-press and the typographic art might have been found a
substitute, however poor, in the lithographic process; and knowledge
might have been widely diffused by the photographic printing powers
of the sun, or even artificial light. But without the telescope and
the microscope, the human eye would have struggled in vain to study
the worlds beyond our own, and the elaborate structures of the organic
and inorganic creation could never have been revealed.--_North-British
Review_, No. 50.
INVENTION OF THE MICROSCOPE.
The earliest magnifying lens of which we have any knowledge was one
rudely made of rock-crystal, which Mr. Layard found, among a number
of glass bowls, in the north-west palace of Nimroud; but no similar
lens has been found or described to induce us to believe that the
microscope, either single or compound, was invented and used as an
instrument previous to the commencement of the seventeenth century.
In the beginning of the first century, however, Seneca alludes to the
magnifying power of a glass globe filled with water; but as he only
states that it made small and indistinct letters appear larger and more
distinct, we cannot consider such a casual remark as the invention of
the single microscope, though it might have led the observer to try the
effect of smaller globes, and thus obtain magnifying powers sufficient
to discover phenomena otherwise invisible.
Lenses of glass were undoubtedly in existence at the time of Pliny;
but at that period, and for many centuries afterwards, they appear
to have been used only as burning or as reading glasses; and no
attempt seems to have been made to form them of so small a size as
to entitle them to be regarded even as the precursors of the single
microscope.--_North-British Review_, No. 50.
The _rock-crystal lens_ found at Nineveh was examined by Sir
David Brewster. It was not entirely circular in its aperture. Its
general form was that of a plano-convex lens, the plane side having
been formed of one of the original faces of the six-sided crystal
quartz, as Sir David ascertained by its action on polarised light:
this was badly polished and scratched. The convex face of the lens
had not been ground in a dish-shaped tool, in the manner in which
lenses are now formed, but was shaped on a lapidary’s wheel, or in
some such manner. Hence it was unequally thick; but its extreme
thickness was 2/10ths of an inch, its focal length being 4½ inches.
It had twelve remains of cavities, which had originally contained
liquids or condensed gases. Sir David has assigned reasons why this
could not be looked upon as an ornament, but a true optical lens.
In the same ruins were found some decomposed glass.
HOW TO MAKE THE FISH-EYE MICROSCOPE.
Very good microscopes may be made with the crystalline lenses of
fish, birds, and quadrupeds. As the lens of fishes is spherical or
spheroidal, it is absolutely necessary, previous to its use, to
determine its optical axis and the axis of vision of the eye from which
it is taken, and place the lens in such a manner that its axis is a
continuation of the axis of our own eye. In no other direction but this
is the albumen of which the lens consists symmetrically disposed in
laminæ of equal density round a given line, which is the axis of the
lens; and in no other direction does the gradation of density, by which
the spherical aberration is corrected, preserve a proper relation to
the axis of vision.
When the lens of any small fish, such as a minnow, a par, or trout,
has been taken out, along with the adhering vitreous humour, from
the eye-ball by cutting the sclerotic coat with a pair of scissors,
it should be placed upon a piece of fine silver-paper previously
freed from its minute adhering fibres. The absorbent nature of
the paper will assist in removing all the vitreous humour from
the lens; and when this is carefully done, by rolling it about
with another piece of silver-paper, there will still remain,
round or near the equator of the lens, a black ridge, consisting
of the processes by which it was suspended in the eye-ball. The
black circle points out to us the true axis of the lens, which
is perpendicular to a plane passing through it. When the small
crystalline has been freed from all the adhering vitreous humour,
the capsule which contains it will have a surface as fine as a
pellicle of fluid. It is then to be dropped from the paper into a
cavity formed by a brass rim, and its position changed till the
black circle is parallel to the circular rim, in which case only
the axis of the lens will be a continuation of the axis of the
observer’s eye.--_Edin. Jour. Science_, vol. ii.
LEUWENHOECK’S MICROSCOPES.
Leuwenhoeck, the father of microscopical discovery, communicated to the
Royal Society, in 1673, a description of the structure of a bee and a
louse, seen by aid of his improved microscopes; and from this period
until his decease in 1723, he regularly transmitted to the society his
microscopical observations and discoveries, so that 375 of his papers
and letters are preserved in the society’s archives, extending over
fifty years. He further bequeathed to the Royal Society a cabinet of
twenty-six microscopes, which he had ground himself and set in silver,
mostly extracted by him from minerals; these microscopes were exhibited
to Peter the Great when he was at Delft in 1698. In acknowledging
the bequest, the council of the Royal Society, in 1724, presented
Leuwenhoeck’s daughter with a handsome silver bowl, bearing the arms of
the society.--_Weld’s History of the Royal Society_, vol. i.
DIAMOND LENSES FOR MICROSCOPES.
In recommending the employment of Diamond and other gems in the
construction of Microscopes, Sir David Brewster has been met with
the objection that they are too expensive for such a purpose; and,
says Sir David, “they certainly are for instruments intended merely
to instruct and amuse. But if we desire to make great discoveries,
to unfold secrets yet hid in the cells of plants and animals, we
must not grudge even a diamond to reveal them. If Mr. Cooper and Sir
James South have given a couple of thousand pounds a piece for a
refracting telescope, in order to study what have been miscalled ‘dots’
and ‘lumps’ of light on the sky; and if Lord Rosse has expended far
greater sums on a reflecting telescope for analysing what has been
called ‘sparks of mud and vapour’ encumbering the azure purity of the
heavens,--why should not other philosophers open their purse, if they
have one, and other noblemen sacrifice some of their household jewels,
to resolve the microscopic structures of our own real world, and
disclose secrets which the Almighty must have intended that we should
know?”--_Proceedings of the British Association_, 1857.
THE EYE AND THE BRAIN SEEN THROUGH A MICROSCOPE.
By a microscopic examination of the retina and optic nerve and
the brain, M. Bauer found them to consist of globules of 1/2800th
to 1/4000th an inch diameter, united by a transparent viscid and
coagulable gelatinous fluid.
MICROSCOPICAL EXAMINATION OF THE HAIR.
If a hair be drawn between the finger and thumb, from the end to
the root, it will be distinctly felt to give a greater resistance
and a different sensation to that which is experienced when drawn
the opposite way: in consequence, if the hair be rubbed between the
fingers, it will only move one way (travelling in the direction of a
line drawn from its termination to its origin from the head or body),
so that each extremity may thus be easily distinguished, even in the
dark, by the touch alone.
The mystery is resolved by the achromatic microscope. A hair viewed on
a dark ground as an _opaque_ object with a high power, not less than
that of a lens of one-thirtieth of an inch focus, and dully illuminated
by a _cup_, the hair is seen to be indented with teeth somewhat
resembling those of a coarse round rasp, but extremely irregular and
rugged: as these incline all in one direction, like those of a common
file, viz. from the origin of the hair towards its extremity, it
sufficiently explains the above singular property.
This is a singular proof of the acuteness of the sense of feeling, for
the said teeth may be felt much more easily than they can be seen. We
may thus understand why a razor will cut a hair in two much more easily
when drawn against its teeth than in the opposite direction.--_Dr.
Goring._
THE MICROSCOPE AND THE SEA.
What myriads has the microscope revealed to us of the rich luxuriance
of animal life in the ocean, and conveyed to our astonished senses
a consciousness of the universality of life! In the oceanic depths
every stratum of water is animated, and swarms with countless hosts of
small luminiferous animalcules, mammaria, crustacea, peridinea, and
circling nereides, which, when attracted to the surface by peculiar
meteorological conditions, convert every wave into a foaming band of
flashing light.
USE OF THE MICROSCOPE TO MINERALOGISTS.
M. Dufour has shown that an imponderable quantity of a substance
can be crystallised; and that the crystals so obtained are quite
characteristic of the substances, as of sugar, chloride of sodium,
arsenic, and mercury. This process may be extremely valuable to the
mineralogist and toxicologist when the substance for examination is too
small to be submitted to tests. By aid of the microscope, also, shells
are measured to the thousandth part of an inch.
FINE DOWN OF QUARTZ.
Sir David Brewster having broken in two a crystal of quartz of a smoky
colour, found both surfaces of the fracture absolutely black; and the
blackness appeared at first sight to be owing to a thin film of opaque
matter which had insinuated itself into the crevice. This opinion,
however, was untenable, as every part of the surface was black, and
the two halves of the crystals could not have stuck together had the
crevice extended across the whole section. Upon further examination Sir
David found that the surface was perfectly transparent by transmitted
light, and that the blackness of the surfaces arose from their being
entirely composed of _a fine down of quartz_, or of short and slender
filaments, whose diameter was so exceedingly small that they were
incapable of reflecting a single ray of the strongest light; and they
could not exceed the _one third of the millionth part of an inch_. This
curious specimen is in the cabinet of her grace the Duchess of Gordon.
MICROSCOPIC WRITING.
Professor Kelland has shown, in Paris, on a spot no larger than
the head of a small pin, by means of powerful microscopes, several
specimens of distinct and beautiful writing, one of them containing
the whole of the Lord’s Prayer written within this minute compass.
In reference to this, two remarkable facts in Layard’s latest work
on Nineveh show that the national records of Assyria were written on
square bricks, in characters so small as scarcely to be legible without
a microscope; in fact, a microscope, as we have just shown, was found
in the ruins of Nimroud.
HOW TO MAKE A MAGIC MIRROR.
Draw a figure with weak gum-water upon the surface of a convex mirror.
The thin film of gum thus deposited on the outline or details of the
figure will not be visible in dispersed daylight; but when made to
reflect the rays of the sun, or those of a divergent pencil, will
be beautifully displayed by the lines and tints occasioned by the
diffraction of light, or the interference of the rays passing through
the film with those which pass by it.
SIR DAVID BREWSTER’S KALEIDOSCOPE.
The idea of this instrument, constructed for the purpose of creating
and exhibiting a variety of beautiful and perfectly symmetrical forms,
first occurred to Sir David Brewster in 1814, when he was engaged in
experiments on the polarisation of light by successive reflections
between plates of glass. The reflectors were in some instances inclined
to each other; and he had occasion to remark the circular arrangement
of the images of a candle round a centre, or the multiplication of the
sectors formed by the extremities of the glass plates. In repeating
at a subsequent period the experiments of M. Biot on the action of
fluids upon light, Sir David Brewster placed the fluids in a trough,
formed by two plates of glass cemented together at an angle; and the
eye being necessarily placed at one end, some of the cement, which had
been pressed through between the plates, appeared to be arranged into a
regular figure. The remarkable symmetry which it presented led to Dr.
Brewster’s investigation of the cause of this phenomenon; and in so
doing he discovered the leading principles of the Kaleidoscope.
By the advice of his friends, Dr. Brewster took out a patent for his
invention; in the specification of which he describes the kaleidoscope
in two different forms. The instrument, however, having been shown
to several opticians in London, became known before he could avail
himself of his patent; and being simple in principle, it was at once
largely manufactured. It is calculated that not less than 200,000
kaleidoscopes were sold in three months in London and Paris; though out
of this number, Dr. Brewster says, not perhaps 1000 were constructed
upon scientific principles, or were capable of giving any thing like a
correct idea of the power of his kaleidoscope.
THE KALEIDOSCOPE THOUGHT TO BE ANTICIPATED.
In the seventh edition of a work on gardening and planting, published
in 1739, by Richard Bradley, F.R.S., late Professor of Botany in the
University of Cambridge, we find the following details of an invention,
“by which the best designers and draughtsmen may improve and help
their fancies. They must choose two pieces of looking-glass of equal
bigness, of the figure of a long square. These must be covered on
the back with paper or silk, to prevent rubbing off the silver. This
covering must be so put on that nothing of it appears about the edges
of the bright side. The glasses being thus prepared, must be laid face
to face, and hinged together so that they may be made to open and shut
at pleasure like the leaves of a book.” After showing how various
figures are to be looked at in these glasses under the same opening,
and how the same figure may be varied under the different openings, the
ingenious artist thus concludes: “If it should happen that the reader
has any number of plans for parterres or wildernesses by him, he may by
this method alter them at his pleasure, and produce such innumerable
varieties as it is not possible the most able designer could ever have
contrived.”
MAGIC OF PHOTOGRAPHY.
Professor Moser of Königsberg has discovered that all bodies, even
in the dark, throw out invisible rays; and that these bodies, when
placed at a small distance from polished surfaces of all kinds, depict
themselves upon such surfaces in forms which remain invisible till
they are developed by the human breath or by the vapours of mercury or
iodine. Even if the sun’s image is made to pass over a plate of glass,
the light tread of its rays will leave behind it an invisible track,
which the human breath will instantly reveal.
Among the early attempts to take pictures by the rays of the sun
was a very interesting and successful experiment made by Dr. Thomas
Young. In 1802, when Mr. Wedgewood was “making profiles by the
agency of light,” and Sir Humphry Davy was “copying on prepared
paper the images of small objects produced by means of the solar
microscope,” Dr. Young was taking photographs upon paper dipped in
a solution of nitrate of silver, of the coloured rings observed
by Newton; and his experiments clearly proved that the agent was
not the luminous rays in the sun’s light, but the invisible or
chemical rays beyond the violet. This experiment is described in
the Bakerian Lecture, 1803.
Niepce (says Mr. Hunt) pursued a physical investigation of the
curious change, and found that all bodies were influenced by this
principle radiated from the sun. Daguerre[14] produced effects from
the solar pencil which no artist could approach; and Talbot and
others extended the application. Herschel took up the inquiry; and
he, with his usual power of inductive search and of philosophical
deduction, presented the world with a class of discoveries which
showed how vast a field of investigation was opening for the
younger races of mankind.
The first attempts in photography, which were made at the
instigation of M. Arago, by order of the French Government, to
copy the Egyptian tombs and temples and the remains of the Aztecs
in Central America, were failures. Although the photographers
employed succeeded to admiration, in Paris, in producing pictures
in a few minutes, they found often that an exposure of an hour
was insufficient under the bright and glowing illumination of a
southern sky.
THE BEST SKY FOR PHOTOGRAPHY.
Contrary to all preconceived ideas, experience proves that the brighter
the sky that shines above the camera the more tardy the action within
it. Italy and Malta do their work slower than Paris. Under the
brilliant light of a Mexican sun, half an hour is required to produce
effects which in England would occupy but a minute. In the burning
atmosphere of India, though photographical the year round, the process
is comparatively slow and difficult to manage; while in the clear,
beautiful, and moreover cool, light of the higher Alps of Europe, it
has been proved that the production of a picture requires many more
minutes, even with the most sensitive preparations, than in the murky
atmosphere of London. Upon the whole, the temperate skies of this
country may be pronounced favourable to photographic action; a fact
for which the prevailing characteristic of our climate may partially
account, humidity being an indispensable condition for the working
state both of paper and chemicals.--_Quarterly Review_, No. 202.
PHOTOGRAPHIC EFFECTS OF LIGHTNING.
The following authenticated instances of this singular phenomenon have
been communicated to the Royal Society by Andrés Poey, Director of the
Observatory at Havana:
Benjamin Franklin, in 1786, stated that about twenty years
previous, a man who was standing opposite a tree that had just been
struck by “a thunderbolt” had on his breast an exact representation
of that tree.
In the New-York _Journal of Commerce_, August 26th, 1853, it is
related that “a little girl was standing at a window, before which
was a young maple-tree; after a brilliant flash of lightning, a
complete image of the tree was found imprinted on her body.”
M. Raspail relates that, in 1855, a boy having climbed a tree for
the purpose of robbing a bird’s nest, the tree was struck, and
the boy thrown upon the ground; on his breast the image of the
tree, with the bird and nest on one of its branches, appeared very
plainly.
M. Olioli, a learned Italian, brought before the Scientific
Congress at Naples the following four instances: 1. In September
1825, the foremast of a brigantine in the Bay of St. Arniro
was struck by lightning, when a sailor sitting under the mast
was struck dead, and on his back was found an impression of a
horse-shoe, similar even in size to that fixed on the mast-head. 2.
A sailor, standing in a similar position, was struck by lightning,
and had on his left breast the impression of the number 4 4, with a
dot between the two figures, just as they appeared at the extremity
of one of the masts. 3. On the 9th October 1836, a young man was
found struck by lightning; he had on a girdle, with some gold
coins in it, which were imprinted on his skin in the order they
were placed in the girdle,--a series of circles, with one point of
contact, being plainly visible. 4. In 1847, Mme. Morosa, an Italian
lady of Lugano, was sitting near a window during a thunderstorm,
and perceived the commotion, but felt no injury; but a flower which
happened to be in the path of the electric current was perfectly
reproduced on one of her legs, and there remained permanently.
M. Poey himself witnessed the following instance in Cuba. On July
24th, 1852, a poplar-tree in a coffee-plantation was struck by
lightning, and on one of the large dry leaves was found an exact
representation of some pine-trees that lay 367 yards distant.
M. Poey considers these lightning impressions to have been produced
in the same manner as the electric images obtained by Moser, Riess,
Karster, Grove, Fox Talbot, and others, either by statical or dynamical
electricity of different intensities. The fact that impressions are
made through the garments is easily accounted for by their rough
texture not preventing the lightning passing through them with the
impression. To corroborate this view, M. Poey mentions an instance of
lightning passing down a chimney into a trunk, in which was found an
inch depth of soot, which must have passed through the wood itself.
PHOTOGRAPHIC SURVEYING.
During the summer of 1854, in the Baltic, the British steamers employed
in examining the enemy’s coasts and fortifications took photographic
views for reference and minute examination. With the steamer moving
at the rate of fifteen knots an hour, the most perfect definitions of
coasts and batteries were obtained. Outlines of the coasts, correct in
height and distance, have been faithfully transcribed; and all details
of the fortresses passed under this photographic review are accurately
recorded.
It is curious to reflect that the aids to photographic development
all date within the last half-century, and are but little older
than photography itself. It was not until 1811 that the chemical
substance called iodine, on which the foundations of all popular
photography rest, was discovered at all; bromine, the only other
substance equally sensitive, not till 1826. The invention of the
electro process was about simultaneous with that of photography
itself. Gutta-percha only just preceded the substance of which
collodion is made; the ether and chloroform, which are used in
some methods, that of collodion. We say nothing of the optical
improvements previously contrived or adapted for the purpose of the
photograph: the achromatic lenses, which correct the discrepancy
between the visual and chemical foci; the double lenses, which
increase the force of the action; the binocular lenses, which
do the work of the stereoscope; nor of the innumerable other
mechanical aids which have sprung up for its use.
THE STEREOSCOPE AND THE PHOTOGRAPH.
When once the availability of one great primitive agent is worked out,
it is easy to foresee how extensively it will assist in unravelling
other secrets in natural science. The simple principle of the
Stereoscope, for instance, might have been discovered a century ago,
for the reasoning which led to it was independent of all the properties
of light; but it could never have been illustrated, far less multiplied
as it now is, without Photography. A few diagrams, of sufficient
identity and difference to prove the truth of the principle, might
have been constructed by hand, for the gratification of a few sages;
but no artist, it is to be hoped, could have been found possessing
the requisite ability and stupidity to execute the two portraits, or
two groups, or two interiors, or two landscapes, identical in every
minutia of the most elaborate detail, and yet differing in point of
view by the inch between the two human eyes, by which the principle is
brought to the level of any capacity. Here, therefore, the accuracy and
insensibility of a machine could alone avail; and if in the order of
things the cheap popular toy which the stereoscope now represents was
necessary for the use of man, the photograph was first necessary for
the service of the stereoscope.--_Quarterly Review_, No. 202.
THE STEREOSCOPE SIMPLIFIED.
When we look at any round object, first with one eye, and then with
the other, we discover that with the right eye we see most of the
right-hand side of the object, and with the left eye most of the
left-hand side. These two images are combined, and we see an object
which we know to be round.
This is illustrated by the _Stereoscope_, which consists of two mirrors
placed each at an angle of 45 deg., or of two semi-lenses turned with
their curved sides towards each other. To view its phenomena two
pictures are obtained by the camera on photographic paper of any object
in two positions, corresponding with the conditions of viewing it with
the two eyes. By the mirrors on the lenses these dissimilar pictures
are combined within the eye, and the vision of an actually solid object
is produced from the pictures represented on a plane surface. Hence the
name of the instrument, which signifies _Solid I see_.--_Hunt’s Poetry
of Science._
PHOTO-GALVANIC ENGRAVING.
That which was the chief aid of Niepce in the humblest dawn of the
art, viz. to transform the photographic plate into a surface capable
of being printed, is in the above process done by the coöperation of
Electricity with Photography. This invention of M. Pretsch, of Vienna,
differs from all other attempts for the same purpose in not operating
upon the photographic tablet itself, and by discarding the usual means
of varnishes and bitings-in. The process is simply this: A glass tablet
is coated with gelatine diluted till it forms a jelly, and containing
bi-chromate of potash, nitrate of silver, and iodide of potassium. Upon
this, when dry, is placed face downwards a paper positive, through
which the light, being allowed to fall, leaves upon the gelatine a
representation of the print. It is then soaked in water; and while
the parts acted upon by the light are comparatively unaffected by the
fluid, the remainder of the jelly swells, and rising above the general
surface, gives a picture in relief, resembling an ordinary engraving
upon wood. Of this intaglio a cast is now taken in gutta-percha, to
which the electro process in copper being applied, a plate or matrix is
produced, bearing on it an exact repetition of the original positive
picture. All that now remains to be done is to repeat the electro
process; and the result is a copper-plate in the necessary relievo, of
which it has been said nature furnished the materials and science the
artist, the inferior workman being only needed to roll it through the
press.--_Quarterly Review_, No. 202.
SCIENCE OF THE SOAP-BUBBLE.
Few of the minor ingenuities of mankind have amused so many individuals
as the blowing of bubbles with soap-lather from the bowl of a
tobacco-pipe; yet how few who in childhood’s careless hours have thus
amused themselves, have in after-life become acquainted with the
beautiful phenomena of light which the soap-bubble will enable us to
illustrate!
Usually the bubble is formed within the bowl of a tobacco-pipe, and
so inflated by blowing through the stem. It is also produced by
introducing a capillary tube under the surface of soapy water, and so
raising a bubble, which may be inflated to any convenient size. It is
then guarded with a glass cover, to prevent its bursting by currents of
air, evaporation, and other causes.
When the bubble is first blown, its form is elliptical, into which it
is drawn by its gravity being resisted; but the instant it is detached
from the pipe, and allowed to float in air, it becomes a perfect
sphere, since the air within presses equally in all directions. There
is also a strong cohesive attraction in the particles of soap and
water, after having been forcibly distended; and as a sphere or globe
possesses less surface than any other figure of equal capacity, it is
of all forms the best adapted to the closest approximation of the
particles of soap and water, which is another reason why the bubble
is globular. The film of which the bubble consists is inconceivably
thin (not exceeding the two-millionth part of an inch); and by the
evaporation from its surface, the contraction and expansion of the air
within, and the tendency of the soap-lather to gravitate towards the
lower part of the bubble, and consequently to render the upper part
still thinner, it follows that the bubble lasts but a few seconds. If,
however, it were blown in a glass vessel, and the latter immediately
closed, it might remain for some time; Dr. Paris thus preserved a
bubble for a considerable period.
Dr. Hooke, by means of the coloured rings upon the soap-bubble, studied
the curious subject of the colours of thin plates, and its application
to explain the colours of natural bodies. Various phenomena were also
discovered by Newton, who thus did not disdain to make a soap-bubble
the object of his study. The colours which are reflected from the upper
surface of the bubble are caused by the decomposition of the light
which falls upon it; and the range of the phenomena is alike extensive
and beautiful.[15]
Newton (says Sir D. Brewster), having covered the soap-bubble with a
glass shade, saw its colours emerge in regular order, like so many
concentric rings encompassing the top of it. As the bubble grew thinner
by the continual subsidence of the water, the rings dilated slowly,
and overspread the whole of it, descending to the bottom, where they
vanished successively. When the colours had all emerged from the top,
there arose in the centre of the rings a small round black spot,
dilating it to more than half an inch in breadth till the bubble
burst. Upon examining the rings between the object-glasses, Newton
found that when they were only _eight_ or _nine_ in number, more than
_forty_ could be seen by viewing them through a prism; and even when
the plate of air seemed all over uniformly white, multitudes of rings
were disclosed by the prism. By means of these observations Newton was
enabled to form his _Scale of Colours_, of great value in all optical
researches.
Dr. Reade has thus produced a permanent soap-bubble:
Put into a six-ounce phial two ounces of distilled water, and set
the phial in a vessel of water boiling on the fire. The water in
the phial will soon boil, and steam will issue from its mouth,
expelling the whole of the atmospheric air from within. Then throw
in a piece of soap about the size of a small pea, cork the phial,
and at the same instant remove it and the vessel from the fire.
Then press the cork farther into the neck of the phial, and cover
it thickly with sealing-wax; and when the contents are cold, a
perfect vacuum will be formed within the bottle,--much better,
indeed, than can be produced by the best-constructed air-pump.
To form a bubble, hold the bottle horizontally in both hands, and
give it a sudden upward motion, which will throw the liquid into a
wave, whose crest touching the upper interior surface of the phial,
the tenacity of the liquid will cause a film to be retained all
round the phial. Next place the phial on its bottom; when the film
will form a section of the cylinder, being nearly but never quite
horizontal. The film will be now colourless, since it reflects all
the light which falls upon it. By remaining at rest for a minute or
two, minute currents of lather will descend by their gravitating
force down the inclined plane formed by the film, the upper part of
which thus becomes drained to the necessary thinness; and this is
the part to be observed.
Several concentric segments of coloured rings are produced; the
colours, beginning from the top, being as follows:
_1st order_: Black, white, yellow, orange, red.
_2d order_: Purple, blue, white, yellow, red.
_3d order_: Purple, blue, green, yellowish-green, white, red.
_4th order_: Purple, blue, green, white, red.
_5th order_: Greenish-blue, very pale red.
_6th order_: Greenish-blue, pink.
_7th order_: Greenish-blue, pink.
As the segments advance they get broader, while the film becomes
thinner and thinner. The several orders disappear upwards as the film
becomes too thin to reflect their colours, until the first order alone
remains, occupying the whole surface of the film. Of this order the
red disappears first, then the orange, and lastly the yellow. The film
is now divided by a line into two nearly equal portions, one black and
the other white. This remains for some time; at length the film becomes
too thin to hold together, and then vanishes. The colours are not faint
and imperfect, but well defined, glowing with gorgeous hues, or melting
into tints so exquisite as to have no rival through the whole circle
of the arts. We quote these details from Mr. Tomlinson’s excellent
_Student’s Manual of Natural Philosophy_.
We find the following anecdote related of Newton at the above
period. When Sir Isaac changed his residence, and went to live in
St. Martin’s Street, Leicester Square, his next-door neighbour was
a widow lady, who was much puzzled by the little she observed of
the habits of the philosopher. A Fellow of the Royal Society called
upon her one day, when, among her domestic news, she mentioned that
some one had come to reside in the adjoining house who, she felt
certain, was a poor crazy gentleman, “because,” she continued,
“he diverts himself in the oddest way imaginable. Every morning,
when the sun shines so brightly that we are obliged to draw the
window-blinds, he takes his seat on a little stool before a tub
of soapsuds, and occupies himself for hours blowing soap-bubbles
through a common clay-pipe, which bubbles he intently watches
floating about till they burst. He is doubtless,” she added, “now
at his favourite amusement, for it is a fine day; do come and look
at him.” The gentleman smiled, and they went upstairs; when, after
looking through the staircase-window into the adjoining court-yard,
he turned and said: “My dear madam, the person whom you suppose
to be a poor lunatic is no other than the great Sir Isaac Newton
studying the refraction of light upon thin plates; a phenomenon
which is beautifully exhibited on the surface of a common
soap-bubble.”
LIGHT FROM QUARTZ.
Among natural phenomena (says Sir David Brewster) illustrative of the
colours of thin plates, we find none more remarkable than one exhibited
by the fracture of a large crystal of quartz of a smoky colour, and
about two and a quarter inches in diameter. The surface of fracture,
in place of being a face or cleavage, or irregularly conchoidal, as we
have sometimes seen it, was filamentous, like a surface of velvet, and
consisted of short fibres, so small as to be incapable of reflecting
light. Their size could not have been greater than the third of the
millionth part of an inch, or one-fourth of the thinnest part of the
soap-bubble when it exhibits the black spot where it bursts.
CAN THE CAT SEE IN THE DARK?
No, in all probability, says the reader; but the opposite popular
belief is supported by eminent naturalists.
Buffon says: “The eyes of the cat shine in the dark somewhat like
diamonds, which throw out during the night the light with which
they were in a manner impregnated during the day.”
Valmont de Bamare says: “The pupil of the cat is during the night
still deeply imbued with the light of the day;” and again, “the
eyes of the cat are during the night so imbued with light that they
then appear very shining and luminous.”
Spallanzani says: “The eyes of cats, polecats, and several other
animals, shine in the dark like two small tapers;” and he adds that
this light is phosphoric.
Treviranus says: “The eyes of the cat _shine where no rays of
light penetrate_; and the light must in many, if not in all, cases
proceed from the eye itself.”
Now, that the eyes of the cat do shine in the dark is to a certain
extent true: but we have to inquire whether by _dark_ is meant the
entire absence of light; and it will be found that the solution of this
question will dispose of several assertions and theories which have for
centuries perplexed the subject.
Dr. Karl Ludwig Esser has published in Karsten’s Archives the results
of an experimental inquiry on the luminous appearance of the eyes of
the cat and other animals, carefully distinguishing such as evolve
light from those which only reflect it. Having brought a cat into a
half-darkened room, he observed from a certain direction that the cat’s
eyes, when _opposite the window_, sparkled brilliantly; but in other
positions the light suddenly vanished. On causing the cat to be held
so as to exhibit the light, and then gradually darkening the room, the
light disappeared by the time the room was made quite dark.
In another experiment, a cat was placed opposite the window in a
darkened room. A few rays were permitted to enter, and by adjusting the
light, one or both of the cat’s eyes were made to shine. In proportion
as the pupil was dilated, the eyes were brilliant. By suddenly
admitting a strong glare of light into the room, the pupil contracted;
and then suddenly darkening the room, the eye exhibited a small round
luminous point, which enlarged as the pupil dilated.
The eyes of the cat sparkle most when the animal is in a lurking
position, or in a state of irritation. Indeed, the eyes of all animals,
as well as of man, appear brighter when in rage than in a quiescent
state, which Collins has commemorated in his Ode on the Passions:
“Next Anger rushed, his eyes on fire.”
This brilliancy is said to arise from an increased secretion of the
lachrymal fluid on the surface of the eye, by which the reflection of
the light is increased. Dr. Esser, in places absolutely dark, never
discovered the slightest trace of light in the eye of the cat; and he
has no doubt that in all cases where cats’ eyes have been seen to shine
in dark places, such as a cellar, light penetrated through some window
or aperture, and fell upon the eyes of the animal as it turned towards
the opening, while the observer was favourably situated to obtain a
view of the reflection.
To prove more clearly that this light does not depend upon the will of
the animal, nor upon its angry passions, experiments were made upon
the head of a dead cat. The sun’s rays were admitted through a small
aperture; and falling immediately upon the eyes, caused them to glow
with a beautiful green light more vivid even than in the case of a
living animal, on account of the increased dilatation of the pupil.
It was also remarked that black and fox-coloured cats gave a brighter
light than gray and white cats.
To ascertain the cause of this luminous appearance Dr. Esser dissected
the eyes of cats, and exposed them to a small regulated amount of light
after having removed different portions. The light was not diminished
by the removal of the cornea, but only changed in colour. The light
still continued after the iris was displaced; but on taking away the
crystalline lens it greatly diminished both in intensity and colour.
Dr. Esser then conjectured that the tapetum in the hinder part of the
eye must form a spot which caused the reflection of the incident
rays of light, and thus produce the shining; and this appeared more
probable as the light of the eye now seemed to emanate from a single
spot. Having taken away the vitreous humour, Dr. Esser observed that
the entire want of the pigment in the hinder part of the choroid coat,
where the optic nerve enters, formed a greenish, silver-coloured,
changeable oblong spot, which was not symmetrical, but surrounded the
optic nerve so that the greater part was above and only the smaller
part below it; wherefore the greater part lay beyond the axis of
vision. It is this spot, therefore, that produces the reflection of the
incident rays of light, and beyond all doubt, according to its tint,
contributes to the different colouring of the light.
It may be as well to explain that the interior of the eye is coated
with a black pigment, which has the same effect as the black colour
given to the inner surface of optical instruments: it absorbs any
rays of light that may be reflected within the eye, and prevents
them from being thrown again upon the retina so as to interfere with
the distinctness of the images formed upon it. The retina is very
transparent; and if the surface behind it, instead of being of a dark
colour, were capable of reflecting light, the luminous rays which had
already acted on the retina would be reflected back again through it,
and not only dazzle from excess of light, but also confuse and render
indistinct the images formed on the retina. Now in the case of the cat
this black pigment, or a portion of it, is wanting; and those parts of
the eye from which it is absent, having either a white or a metallic
lustre, are called the tapetum. The smallest portion of light entering
from it is reflected as by a concave mirror; and hence it is that the
eyes of animals provided with this structure are luminous in a very
faint light.
These experiments and observations show that the shining of the eyes
of the cat does not arise from a phosphoric light, but only from a
reflected light; that consequently it is not an effect of the will of
the animal, or of violent passions; that their shining does not appear
in absolute darkness; and that it cannot enable the animal to move
securely in the dark.
It has been proved by experiment that there exists a set of rays of
light of far higher refrangibility than those seen in the ordinary
Newtonian spectrum. Mr. Hunt considers it probable that these highly
refrangible rays, although under ordinary circumstances invisible
to the human eye, may be adapted to produce the necessary degree
of excitement upon which vision depends in the optic nerves of the
night-roaming animals. The bat, the owl, and the cat may see in the
gloom of the night by the aid of rays which are invisible to, or
inactive on, the eyes of man or those animals which require the light
of day for perfect vision.
Astronomy.
THE GREAT TRUTHS OF ASTRONOMY.
The difficulty of understanding these marvellous truths has been
glanced at by an old divine (see _Things not generally Known_, p.
1); but the rarity of their full comprehension by those unskilled in
mathematical science is more powerfully urged by Lord Brougham in these
cogent terms:
Satisfying himself of the laws which regulate the mutual actions
of the planetary bodies, the mathematician can convince himself of
a truth yet more sublime than Newton’s discovery of gravitation,
though flowing from it; and must yield his assent to the marvellous
position, that all the irregularities occasioned in the system
of the universe by the mutual attraction of its members are
periodical, and subject to an eternal law, which prevents them from
ever exceeding a stated amount, and secures through all time the
balanced structure of a universe composed of bodies whose mighty
bulk and prodigious swiftness of motion mock the utmost efforts
of the human imagination. All these truths are to the skilful
mathematician as thoroughly known, and their evidence is as clear,
as the simplest proposition of arithmetic to common understandings.
But how few are those who thus know and comprehend them! Of all
the millions that thoroughly believe these truths, certainly not a
thousand individuals are capable of following even any considerable
portion of the demonstrations upon which they rest; and probably
not a hundred now living have ever gone through the whole steps
of these demonstrations.--_Dissertations on Subjects of Science
connected with Natural Theology_, vol. ii.
Sir David Brewster thus impressively illustrates the same subject:
Minds fitted and prepared for this species of inquiry are
capable of appreciating the great variety of evidence by
which the truths of the planetary system are established; but
thousands of individuals, and many who are highly distinguished
in other branches of knowledge, are incapable of understanding
such researches, and view with a sceptical eye the great and
irrefragable truths of astronomy.
That the sun is stationary in the centre of our system; that
the earth moves round the sun, and round its own axis; that
the diameter of the earth is 8000 miles, and that of the sun
_one hundred and ten times as great_; that the earth’s orbit is
190,000,000 of miles in breadth; and that if this immense space
were filled with light, it would appear only like a luminous point
at the nearest fixed star,--are positions absolutely unintelligible
and incredible to all who have not carefully studied the subject.
To millions of our species, then, the great Book of Nature is
absolutely sealed; though it is in the power of all to unfold its
pages, and to peruse those glowing passages which proclaim the
power and wisdom of its Author.
ASTRONOMY AND DATES ON MONUMENTS.
Astronomy is a useful aid in discovering the Dates of ancient
Monuments. Thus, on the ceiling of a portico among the ruins of
Tentyris are the twelve signs of the Zodiac, placed according to the
apparent motion of the sun. According to this Zodiac, the summer
solstice is in Leo; from which it is easy to compute, by the precession
of the equinoxes of 50″·1 annually, that the Zodiac of Tentyris must
have been made 4000 years ago.
Mrs. Somerville relates that she once witnessed the ascertainment of
the date of a Papyrus by means of astronomy. The manuscript was found
in Egypt, in a mummy-case; and its antiquity was determined by the
configuration of the heavens at the time of its construction. It proved
to be a horoscope of the time of Ptolemy.
“THE CRYSTAL VAULT OF HEAVEN.”
This poetic designation dates back as far as the early period of
Anaximenes; but the first clearly defined signification of the idea on
which the term is based occurs in Empedocles. This philosopher regarded
the heaven of the fixed stars as a solid mass, formed from the ether
which had been rendered crystalline by the action of fire.
In the Middle Ages, the fathers of the Church believed the firmament to
consist of from seven to ten glassy strata, incasing each other like
the different coatings of an onion. This supposition still keeps its
ground in some of the monasteries of southern Europe, where Humboldt
was greatly surprised to hear a venerable prelate express an opinion in
reference to the fall of aerolites at Aigle, that the bodies we called
meteoric stones with vitrified crusts were not portions of the fallen
stone itself, but simply fragments of the crystal vault shattered by it
in its fall.
Empedocles maintained that the fixed stars were riveted to the
crystal heavens; but that the planets were free and unconstrained.
It is difficult to conceive how, according to Plato in the _Timæus_,
the fixed stars, riveted as they are to solid spheres, could rotate
independently.
Among the ancient views, it may be mentioned that the equal distance
at which the stars remained, while the whole vault of heaven seemed to
move from east to west, had led to the idea of a firmament and a solid
crystal sphere, in which Anaximenes (who was probably not much later
than Pythagoras) had conjectured that the stars were riveted like nails.
MUSIC OF THE SPHERES.
The Pythagoreans, in applying their theory of numbers to the
geometrical consideration of the five regular bodies, to the musical
intervals of tone which determine a word and form different kinds
of sounds, extended it even to the system of the universe itself;
supposing that the moving, and, as it were, vibrating planets, exciting
sound-waves, must produce a _spheral music_, according to the harmonic
relations of their intervals of space. “This music,” they add, “would
be perceived by the human ear, if it was not rendered insensible by
extreme familiarity, as it is perpetual, and men are accustomed to it
from childhood.”
The Pythagoreans affirm, in order to justify the reality of the
tones produced by the revolution of the spheres, that hearing takes
place only where there is an alternation of sound and silence. The
inaudibility of the spheral music is also accounted for by its
overpowering the senses. Aristotle himself calls the Pythagorean
tone-myth pleasing and ingenious, but untrue.
Plato attempted to illustrate the tones of the universe in an
agreeable picture, by attributing to each of the planetary spheres a
syren, who, supported by the stern daughters of Necessity, the three
Fates, maintain the eternal revolution of the world’s axis. Mention
is constantly made of the harmony of the spheres, though generally
reproachfully, throughout the writings of Christian antiquity and the
Middle Ages, from Basil the Great to Thomas Aquinas and Petrus Alliacus.
At the close of the sixteenth century, Kepler revived these musical
ideas, and sought to trace out the analogies between the relations of
tone and the distances of the planets; and Tycho Brahe was of opinion
that the revolving conical bodies were capable of vibrating the
celestial air (what we now call “resisting medium”) so as to produce
tones. Yet Kepler, although he had talked of Venus and the Earth
sounding sharp in aphelion and flat in perihelion, and the highest tone
of Jupiter and that of Venus coinciding in flat accord, positively
declared there to be “no such things as sounds among the heavenly
bodies, nor is their motion so turbulent as to elicit noise from the
attrition of the celestial air.” (See _Things not generally Known_, p.
44.)
“MORE WORLDS THAN ONE.”
Although this opinion was maintained incidentally by various writers
both on astronomy[16] and natural religion, yet M. Fontenelle was the
first individual who wrote a treatise on the _Plurality of Worlds_,
which appeared in 1685, the year before the publication of Newton’s
_Principia_. Fontenelle’s work consists of five chapters: 1. The earth
is a planet which turns round its axis, and also round the sun. 2. The
moon is a habitable world. 3. Particulars concerning the world in the
moon, and that the other planets are also inhabited. 4. Particulars of
the worlds of Venus, Mercury, Mars, Jupiter, and Saturn. 5. The fixed
stars are as many suns, each of which illuminates a world. In a future
edition, 1719, Fontenelle added, 6. New thoughts which confirm those in
the preceding conversations, and the latest discoveries which have been
made in the heavens. The next work on the subject was the _Theory of
the Universe, or Conjectures concerning the Celestial Bodies and their
Inhabitants_, 1698, by Christian Huygens, the contemporary of Newton.
The doctrine is maintained by almost all the distinguished astronomers
and writers who have flourished since the true figure of the earth was
determined. Giordano Bruna of Nola, Kepler, and Tycho Brahe, believed
in it; and Cardinal Cusa and Bruno, before the discovery of binary
systems among the stars, believed also that the stars were inhabited.
Sir Isaac Newton likewise adopted the belief; and Dr. Bentley, Master
of Trinity College, Cambridge, in his eighth sermon on the Confutation
of Atheism from the origin and frame of the world, has ably maintained
the same doctrine. In our own day we may number among its supporters
the distinguished names of the Marquis de la Place, Sir William and
Sir John Herschel, Dr. Chalmers, Isaac Taylor, and M. Arago. Dr.
Chalmers maintains the doctrine in his _Astronomical Discourses_, which
one Alexander Maxwell (who did not believe in the grand truths of
astronomy) attempted to controvert, in 1820, in a chapter of a volume
entitled _Plurality of Worlds_.
Next appeared _Of a Plurality of Worlds_, attributed to the Rev. Dr.
Whewell, Master of Trinity College, Cambridge; urging the theological
not less than the scientific reasons for believing in the old tradition
of a single world, and maintaining that “the earth is really the
largest planetary body in the solar system,--its domestic hearth,
and the only world in the universe.” “I do not pretend,” says Dr.
Whewell, “to disprove the plurality of worlds; but I ask in vain for
any argument which makes the doctrine probable.” “It is too remote
from knowledge to be either proved or disproved.” Sir David Brewster
has replied to Dr. Whewell’s Essay, in _More Worlds than One, the
Creed of the Philosopher and the Hope of the Christian_, emphatically
maintaining that analogy strongly countenances the idea of all the
solar planets, if not all worlds in the universe, being peopled with
creatures not dissimilar in being and nature to the inhabitants
of the earth. This view is supported in _Scientific Certainties of
Planetary Life_, by T. C. Simon, who well treats one point of the
argument--that mere distance of the planets from the central sun
does not determine the condition as to light and heat, but that the
density of the ethereal medium enters largely into the calculation. Mr.
Simon’s general conclusion is, that “neither on account of deficient
or excessive heat, nor with regard to the density of the materials,
nor with regard to the force of gravity on the surface, is there the
slightest pretext for supposing that all the planets of our system
are not inhabited by intellectual creatures with animal bodies like
ourselves,--moral beings, who know and love their great Maker, and
who wait, like the rest of His creation, upon His providence and upon
His care.” One of the leading points of Dr. Whewell’s Essay is, that
we should not elevate the conjectures of analogy into the rank of
scientific certainties; and that “the force of all the presumptions
drawn from physical reasoning for the opinion of planets and stars
being either inhabited or uninhabited is so small, that the belief of
all thoughtful persons on this subject will be determined by moral,
metaphysical, and theological considerations.”
WORLDS TO COME--ABODES OF THE BLEST.
Sir David Brewster, in his eloquent advocacy of the doctrine of “more
worlds than one,” thus argues for their peopling:
Man, in his future state of existence, is to consist, as at
present, of a spiritual nature residing in a corporeal frame. He
must live, therefore, upon a material planet, subject to all the
laws of matter, and performing functions for which a material body
is indispensable. We must consequently find for the race of Adam,
if not races that may have preceded him, a material home upon which
they may reside, or by which they may travel, by means unknown to
us, to other localities in the universe. At the present hour, the
inhabitants of the earth are nearly _a thousand millions_; and
by whatever process we may compute the numbers that have existed
before the present generation, and estimate those that are yet to
inherit the earth, we shall obtain a population which the habitable
parts of our globe could not possibly accommodate. If there is not
room, then, on our earth for the millions of millions of beings who
have lived and died upon its surface, and who may yet live and die
during the period fixed for its occupation by man, we can scarcely
doubt that their future abode must be on some of the primary or
secondary planets of the solar system, whose inhabitants have
ceased to exist like those on the earth, or upon planets in our own
or in other systems which have been in a state of preparation, as
our earth was, for the advent of intellectual life.
“GAUGING THE HEAVENS.”
Sir William Herschel, in 1785, conceived the happy idea of counting
the number of stars which passed at different heights and in various
directions over the field of view, of fifteen minutes in diameter,
of his twenty-feet reflecting telescope. The field of view each time
embraced only 1/833000th of the whole heavens; and it would therefore
require, according to Struve, eighty-three years to gauge the whole
sphere by a similar process.
VELOCITY OF THE SOLAR SYSTEM.
M. F. W. G. Struve gives as the splendid result of the united studies
of MM. Argelander, O. Struve, and Peters, grounded on observations
made at the three Russian observatories of Dorpat, Abo, and Pulkowa,
“that the velocity of the motion of the solar system in space is such
that the sun, with all the bodies which depend upon it, advances
annually towards the constellation Hercules[17] 1·623 times the radius
of the earth’s orbit, or 33,550,000 geographical miles. The possible
error of this last number amounts to 1,733,000 geographical miles, or
to a _seventh_ of the whole value. We may, then, wager 400,000 to 1
that the sun has a proper progressive motion, and 1 to 1 that it is
comprised between the limits of thirty-eight and twenty-nine millions
of geographical miles.”
That is, taking 95,000,000 of English miles as the mean radius of
the Earth’s orbit, we have 95 × 1·623 = 154·185 millions of miles;
and consequently,
English Miles.
The velocity of the Solar System 154,185,000 in the year.
” ” 422,424 in a day.
” ” 17,601 in an hour.
” ” 293 in a minute.
” ” 57 in a second.
The Sun and all his planets, primary and secondary, are therefore
now in rapid motion round an invisible focus. To that now dark and
mysterious centre, from which no ray, however feeble, shines, we
may in another age point our telescopes, detecting perchance the
great luminary which controls our system and bounds its path: into
that vast orbit man, during the whole cycle of his race, may never
be allowed to round.--_North-British Review_, No. 16.
NATURE OF THE SUN.
M. Arago has found, by experiments with the polariscope, that the light
of gaseous bodies is natural light when it issues from the burning
surface; although this circumstance does not prevent its subsequent
complete polarisation, if subjected to suitable reflections or
refractions. Hence we obtain _a most simple method of discovering
the nature of the sun_ at a distance of forty millions of leagues.
For if the light emanating from the margin of the sun, and radiating
from the solar substance _at an acute angle_, reach us without having
experienced any sensible reflections or refractions in its passage
to the earth, and if it offer traces of polarisation, the sun must
be _a solid or a liquid body_. But if, on the contrary, the light
emanating from the sun’s margin give no indications of polarisation,
the _incandescent_ portion of the sun must be _gaseous_. It is by means
of such a methodical sequence of observations that we may acquire
exact ideas regarding the physical constitution of the sun.--_Note to
Humboldt’s Cosmos_, vol. iii.
STRUCTURE OF THE LUMINOUS DISC OF THE SUN.
The extraordinary structure of the _fully luminous_ Disc of the Sun, as
seen through Sir James South’s great achromatic, in a drawing made by
Mr. Gwilt, resembles compressed curd, or white almond-soap, or a mass
of asbestos fibres, lying in a _quaquaversus_ direction, and compressed
into a solid mass. There can be no illusion in this phenomenon; it
is seen by every person with good vision, and on every part of the
sun’s luminous surface or envelope, which is thus shown to be not a
_flame_, but a soft solid or thick fluid, maintained in an incandescent
state by subjacent heat, capable of being disturbed by differences of
temperature, and broken up as we see it when the sun is covered with
spots or openings in the luminous matter.--_North-British Review_, No.
16.
Copernicus named the sun the lantern of the world (_lucerna
mundi_); and Theon of Smyrna called it the heart of the universe.
The mass of the sun is, according to Encke’s calculation of
Sabine’s pendulum formula, 359,551 times that of the earth, or
355,499 times that of the earth and moon together; whence the
density of the sun is only about ¼ (or more accurately 0·252) that
of the earth. The volume of the sun is 600 times greater, and its
mass, according to Galle, 738 times greater, than that of all the
planets combined. It may assist the mind in conceiving a sensuous
image of the magnitude of the sun, if we remember that if the solar
sphere were entirely hollowed out, and the earth placed in its
centre, there would still be room enough for the moon to describe
its orbit, even if the radius of the latter were increased 160,000
geographical miles. A railway-engine, moving at the rate of thirty
miles an hour, would require 360 years to travel from the earth to
the sun. The diameter of the sun is rather more than one hundred
and eleven times the diameter of the earth. Therefore the volume or
bulk of the sun must be nearly _one million four hundred thousand_
times that of the earth. Lastly, if all the bodies composing the
solar system were formed into one globe, it would be only about the
five-hundredth part of the size of the sun.
GREAT SIZE OF THE SUN ON THE HORIZON EXPLAINED.
The dilated size (generally) of the Sun or Moon, when seen near the
horizon, beyond what they appear to have when high up in the sky, has
nothing to do with refraction. It is an illusion of the judgment,
arising from the terrestrial objects interposed, or placed in close
comparison with them. In that situation we view and judge of them
as we do of terrestrial objects--in detail, and with an acquired
attention to parts. Aloft we have no association to guide us, and their
insulation in the expanse of the sky leads us rather to undervalue
than to over-rate their apparent magnitudes. Actual measurement with
a proper instrument corrects our error, without, however, dispelling
our illusion. By this we learn that the sun, when just on the horizon,
subtends at our eyes almost exactly the same, and the moon a materially
_less_, angle than when seen at a greater altitude in the sky, owing to
its greater distance from us in the former situation as compared with
the latter.--_Sir John Herschel’s Outlines._
TRANSLATORY MOTION OF THE SUN.
This phenomenon is the progressive motion of the centre of gravity of
the whole solar system in universal space. Its velocity, according
to Bessel, is probably four millions of miles daily, in a _relative_
velocity to that of 61 Cygni of at least 3,336,000 miles, or more than
double the velocity of the revolution of the earth in her orbit round
the sun. This change of the entire solar system would remain unknown
to us, if the admirable exactness of our astronomical instruments of
measurement, and the advancement recently made in the art of observing,
did not cause our progress towards remote stars to be perceptible,
like an approximation to the objects of a distant shore in apparent
motion. The proper motion of the star 61 Cygni, for instance, is so
considerable, that it has amounted to a whole degree in the course of
700 years.--_Humboldt’s Cosmos_, vol. i.
THE SUN’S LIGHT COMPARED WITH TERRESTRIAL LIGHTS.
Mr. Ponton has by means of a simple monochromatic photometer
ascertained that a small surface, illuminated by mean solar light, is
444 times brighter than when it is illuminated by a moderator lamp, and
1560 times brighter than when it is illuminated by a wax-candle (short
six in the lb.)--the artificial light being in both instances placed at
two inches’ distance from the illuminated surface. And three electric
lights, each equal to 520 wax-candles, will render a small surface as
bright as when it is illuminated by mean sunshine.
It is thence inferred, that a stratum occupying the entire surface of
the sphere of which the earth’s distance from the sun is the radius,
and consisting of three layers of flame, each 1/1000th of an inch
in thickness, each possessing a brightness equal to that of such an
electric light, and all three embraced within a thickness of 1/40th of
an inch, would give an amount of illumination equal in quantity and
intensity to that of the sun at the distance of 95 millions of miles
from his centre.
And were such a stratum transferred to the surface of the sun, where it
would occupy 46,275 times less area, its thickness would be increased
to 94 feet, and it would embrace 138,825 layers of flame, equal in
brightness to the electric light; but the same effect might be produced
by a stratum about nine miles in thickness, embracing 72 millions of
layers, each having only a brightness equal to that of a wax-candle.[18]
ACTINIC POWER OF THE SUN.
Mr. J. J. Waterston, in 1857, made at Bombay some experiments on the
photographic power of the sun’s direct light, to obtain data in an
inquiry as to the possibility of measuring the diameter of the sun to
a very minute fraction of a second, by combining photography with the
principle of the electric telegraph; the first to measure the element
space, the latter the element time. The result is that about 1/20000th
of a second is sufficient exposure to the direct light of the sun to
obtain a distinct mark on a sensitive collodion plate, when developed
by the usual processes; and the duration of the sun’s full action on
any one point is about 1/9000th of a second.
M. Schatt, a young painter of Berlin, after 1500 experiments, succeeded
in establishing a scale of all the shades of black which the action of
the sun produces on photographic paper; so that by comparing the shade
obtained at any given moment on a certain paper with that indicated on
the scale, the exact force of the sun’s light may be determined.
HEATING POWER OF THE SUN.
All moving power has its origin in the rays of the sun. While
Stephenson’s iron tubular railway-bridge over the Menai Straits, 400
feet long, bends but half an inch under the heaviest pressure of a
train, it will bend up an inch and a half from its usual horizontal
line when the sun shines on it for some hours. The Bunker-Hill
monument, near Boston, U.S., is higher in the evening than in the
morning of a sunny day; the little sunbeams enter the pores of the
stone like so many wedges, lifting it up.
In winter, the Earth is nearer the Sun by about 1/30 than in summer;
but the rays strike the northern hemisphere more obliquely in winter
than the other half year.
M. Pouillet has estimated, with singular ingenuity, from a series of
observations made by himself, that the whole quantity of heat which the
Earth receives annually from the Sun is such as would be sufficient to
melt a stratum of ice covering the entire globe forty-six feet deep.
By the action of the sun’s rays upon the earth, vegetables, animals,
and man, are in their turn supported; the rays become likewise, as
it were, a store of heat, and “the sources of those great deposits
of dynamical efficiency which are laid up for human use in our coal
strata” (_Herschel_).
A remarkable instance of the power of the sun’s rays is recorded at
Stonehouse Point, Devon, in the year 1828. To lay the foundation of a
sea-wall the workmen had to descend in a diving-bell, which was fitted
with convex glasses in the upper part, by which, on several occasions
in clear weather, the sun’s rays were so concentrated as to burn the
labourers’ clothes when opposed to the focal point, and this when the
bell was twenty-five feet under the surface of the water!
CAUSE OF DARK COLOUR OF THE SKIN.
Darkness of complexion has been attributed to the sun’s power from the
age of Solomon to this day,--“Look not upon me, because I am black,
because the sun hath looked upon me:” and there cannot be a doubt
that, to a certain degree, the opinion is well founded. The invisible
rays in the solar beams, which change vegetable colour, and have been
employed with such remarkable effect in the daguerreotype, act upon
every substance on which they fall, producing mysterious and wonderful
changes in their molecular state, man not excepted.--_Mrs. Somerville._
EXTREME SOLAR HEAT.
The fluctuation in the sun’s direct heating power amounts to 1/15th,
which is too considerable a fraction of the whole intensity not
to aggravate in a serious degree the sufferings of those who are
exposed to it in thirsty deserts without shelter. The amount of these
sufferings, in the interior of Australia for instance, are of the
most frightful kind, and would seem far to exceed what have ever been
undergone by travellers in the northern deserts of Africa. Thus
Captain Sturt, in his account of his Australian exploration, says:
“The ground was almost a molten surface; and if a match accidentally
fell upon it, it immediately ignited.” Sir John Herschel has observed
the temperature of the surface soil in South Africa as high as 159°
Fahrenheit. An ordinary lucifer-match does not ignite when simply
pressed upon a smooth surface at 212°; but _in the act of withdrawing
it_ it takes fire, and the slightest friction upon such a surface of
course ignites it.
HOW DR. WOLLASTON COMPARED THE LIGHT OF THE SUN AND THE FIXED STARS.
In order to compare the Light of the Sun with that of a Star, Dr.
Wollaston took as an intermediate object of comparison the light of a
candle reflected from a bulb about a quarter of an inch in diameter,
filled with quicksilver; and seen by one eye through a lens of two
inches focus, at the same time that the star on the sun’s image,
_placed at a proper distance_, was viewed by the other eye through a
telescope. The mean of various trials seemed to show that the light
of Sirius is equal to that of the sun seen in a glass bulb 1/10th of
an inch in diameter, at the distance of 210 feet; or that they are in
the proportion of one to ten thousand millions: but as nearly one half
of this light is lost by reflection, the real proportion between the
light from Sirius and the sun is not greater than that of one to twenty
thousand millions.
“THE SUN DARKENED.”
Humboldt selects the following example from historical records as to
the occurrence of a sudden decrease in the light of the Sun:
A.D. 33, the year of the Crucifixion. “Now from the sixth hour
there was darkness over all the land till the ninth hour” (_St.
Matthew_ xxvii. 45). According to _St. Luke_ (xxiii. 45), “the
sun was darkened.” In order to explain and corroborate these
narrations, Eusebius brings forward an eclipse of the sun in the
202d Olympiad, which had been noticed by the chronicler Phlegon
of Tralles (_Ideler_, _Handbuch der Mathem. Chronologie_, Bd. ii.
p. 417). Wurn, however, has shown that the eclipse which occurred
during this Olympiad, and was visible over the whole of Asia
Minor, must have happened as early as the 24th of November 29 A.D.
The day of the Crucifixion corresponded with the Jewish Passover
(_Ideler_, Bd. i. pp. 515-520), on the 14th of the month Nisan, and
the Passover was always celebrated at the time of the _full moon_.
The sun cannot therefore have been darkened for three hours by the
moon. The Jesuit Scheiner thinks the decrease in the light might be
ascribed to the occurrence of large sun-spots.
THE SUN AND TERRESTRIAL MAGNETISM.
The important influence exerted by the Sun’s body, as a mass, upon
Terrestrial Magnetism, is confirmed by Sabine in the ingenious
observation, that the period at which the intensity of the magnetic
force is greatest, and the direction of the needle most near to the
vertical line, falls in both hemispheres between the months of October
and February; that is to say, precisely at the time when the earth is
nearest to the sun, and moves in its orbit with the greatest velocity.
IS THE HEAT OF THE SUN DECREASING?
The Heat of the Sun is dissipated and lost by radiation, and must
be progressively diminished unless its thermal energy be supplied.
According to the measurements of M. Pouillet, the quantity of heat
given out by the sun in a year is equal to that which would be produced
by the combustion of a stratum of coal seventeen miles in thickness;
and if the sun’s capacity for heat be assumed equal to that of water,
and the heat be supposed drawn uniformly from its entire mass, its
temperature would thereby undergo a diminution of 20·4° Fahr. annually.
On the other hand, there is a vast store of force in our system capable
of conversion into heat. If, as is indicated by the small density of
the sun, and by other circumstances, that body has not yet reached the
condition of incompressibility, we have in the future approximation of
its parts a fund of heat, probably quite large enough to supply the
wants of the human family to the end of its sojourn here. It has been
calculated that an amount of condensation which would diminish the
diameter of the sun by only the ten-thousandth part, would suffice to
restore the heat emitted in 2000 years.
UNIVERSAL SUN-DIAL.
Mr. Sharp, of Dublin, exhibited to the British Association in 1849 a
Dial, consisting of a cylinder set to the day of the month, and then
elevated to the latitude. A thin plane of metal, in the direction of
its axis, is then turned by a milled head below it till the shadow is
a minimum, when a dial on the top shows the hours by one hand, and the
minutes by another, to the precision of about three minutes.
LENGTH OF DAYS AT THE POLES.
During the summer, in the northern hemisphere, places near the North
Pole are in _continual sunlight_--the sun never sets to them; while
during that time places near the South Pole never see the sun. When it
is summer in the southern hemisphere, and the sun shines on the South
Pole without setting, the North Pole is entirely deprived of his light.
Indeed, at the Poles there is but _one day and one night_; for the sun
shines for six months together on one Pole, and the other six months on
the other Pole.
HOW THE DISTANCE OF THE SUN IS ASCERTAINED BY THE YARD-MEASURE.
Professor Airy, in his _Six Lectures on Astronomy_, gives a masterly
analysis of a problem of considerable intricacy, viz. the determination
of the parallax of the sun, and consequently of his distance, by
observations of the transit of Venus, the connecting link between
measures upon the earth’s surface and the dimensions of our system.
The further step of investigating the parallax, and consequently the
distance of the fixed stars (where that is practicable), is also
elucidated; and the author, with evident satisfaction, thus sums up the
several steps:
By means of a yard-measure, a base-line in a survey was measured;
from this, by the triangulations and computations of a survey,
an arc of meridian on the earth was measured; from this, with
proper observations with the zenith sector, the surveys being also
repeated on different parts of the earth, the earth’s form and
dimensions were ascertained; from these, and a previous independent
knowledge of the proportions of the distances of the earth and
other planets from the sun, with observations of the transit of
Venus, the sun’s distance is determined; and from this, with
observations leading to the parallax of the stars, the distance
of the stars is determined. And _every step in the process can be
distinctly referred to its basis, that is, the yard-measure_.
HOW THE TIDES ARE PRODUCED BY THE SUN AND MOON.
Each of these bodies excites, by its attraction upon the waters of the
sea, two gigantic waves, which flow in the same direction round the
world as the attracting bodies themselves apparently do. The two waves
of the moon, on account of her greater nearness, are about 3½ times as
large as those excited by the sun. One of these waves has its crest on
the quarter of the earth’s surface which is turned towards the moon;
the other is at the opposite side. Both these quarters possess the flow
of the tide, while the regions which lie between have the ebb. Although
in the open sea the height of the tide amounts to only about three
feet, and only in certain narrow channels, where the moving water is
squeezed together, rises to thirty feet, the might of the phenomenon
is nevertheless manifest from the calculation of Bessel, according to
which a quarter of the earth covered by the sea possesses during the
flow of the tide about 25,000 cubic miles of water more than during the
ebb; and that, therefore, such a mass of water must in 6¼ hours flow
from one quarter of the earth to the other.--_Professor Helmholtz._
SPOTS ON THE SUN.
Sir John Herschel describes these phenomena, when watched from day to
day, or even from hour to hour, as appearing to enlarge or contract,
to change their forms, and at length disappear altogether, or to break
out anew in parts of the surface where none were before. Occasionally
they break up or divide into two or more. The scale on which their
movements takes place is immense. A single second of angular measure,
as seen from the earth, corresponds on the sun’s disc to 461 miles; and
a circle of this diameter (containing therefore nearly 167,000 square
miles) is the least space which can be distinctly discerned on the sun
as a _visible area_. Spots have been observed, however, whose linear
diameter has been upwards of 45,000 miles; and even, if some records
are to be trusted, of very much greater extent. That such a spot should
close up in six weeks time (for they seldom last much longer), its
borders must approach at the rate of more than 1000 miles a-day.
The same astronomer saw at the Cape of Good Hope, on the 29th March
1837, a solar spot occupying an area of near _five square minutes_,
equal to 3,780,000,000 square miles. “The black centre of the spot of
May 25th, 1837 (not the tenth part of the preceding one), would have
allowed the globe of our earth to drop through it, leaving a thousand
miles clear of contact on all sides of that tremendous gulf.” For such
an amount of disturbance on the sun’s atmosphere, what reason can be
assigned?
The Rev. Mr. Dawes has invented a peculiar contrivance, by means of
which he has been enabled to scrutinise, under high magnifying power,
minute portions of the solar disc. He places a metallic screen, pierced
with a very small hole, in the focus of the telescope, where the image
of the sun is formed. A small portion only of the image is thus allowed
to pass through, so that it may be examined by the eye-piece without
inconveniencing the observer by heat or glare. By this arrangement,
Mr. Dawes has observed peculiarities in the constitution of the sun’s
surface which are discernible in no other way.
Before these observations, the dark spots seen on the sun’s surface
were supposed to be portions of the solid body of the sun, laid bare to
our view by those immense fluctuations in the luminous regions of its
atmosphere to which it appears to be subject. It now appears that these
dark portions are only an additional and inferior stratum of a very
feebly luminous or illuminated portion of the sun’s atmosphere. This
again in its turn Mr. Dawes has frequently seen pierced with a smaller
and usually much more rounded aperture, which would seem at last to
afford a view of the real solar surface of most intense blackness.
M. Schwabe, of Dessau, has discovered that the abundance or paucity
of spots displayed by the sun’s surface is subject to a law of
periodicity. This has been confirmed by M. Wolf, of Berne, who shows
that the period of these changes, from minimum to minimum, is 11 years
and 11-hundredths of a year, being exactly at the rate of nine periods
per century, the last year of each century being a year of minimum. It
is strongly corroborative of the correctness both of M. Wolf’s period
and also of the periodicity itself, that of all the instances of the
appearance of spots on the sun recorded in history, even before the
invention of the telescope, or of remarkable deficiencies in the sun’s
light, of which there are great numbers, only two are found to deviate
as much as two years from M. Wolf’s epochs. Sir William Herschel
observed that the presence or absence of spots had an influence on the
temperature of the seasons; his observations have been fully confirmed
by M. Wolf. And, from an examination of the chronicles of Zurich from
A.D. 1000 to A.D. 1800, he has come to the conclusion “that years rich
in solar spots are in general drier and more fruitful than those of an
opposite character; while the latter are wetter and more stormy than
the former.”
The most extraordinary fact, however, in connection with the spots on
the sun’s surface, is the singular coincidence of their periods with
those great disturbances in the magnetic system of the earth to which
the epithet of “magnetic storms” has been affixed.
These disturbances, during which the magnetic needle is greatly
and universally agitated (not in a particular limited locality,
but at one and the same instant of time over whole continents, or
even over the whole earth), are found, so far as observation has
hitherto extended, to maintain a parallel, both in respect of their
frequency of occurrence and intensity in successive years, with the
abundance and magnitude of the spots in the same years, too close
to be regarded as fortuitous. The coincidence of the epochs of
maxima and minima in the two series of phenomena amounts, indeed,
to identity; a fact evidently of most important significance, but
which neither astronomical nor magnetic science is yet sufficiently
advanced to interpret.--_Herschel’s Outlines._
The signification and connection of the above varying phenomena
(Humboldt maintains) can never be manifested in their entire importance
until an uninterrupted series of representations of the sun’s spots
can be obtained by the aid of mechanical clock-work and photographic
apparatus, as the result of prolonged observations during the many
months of serene weather enjoyed in a tropical climate.
M. Schwabe has thus distinguished himself as an indefatigable
observer of the sun’s spots, for his researches received the Royal
Astronomical Society’s Medal in 1857. “For thirty years,” said
the President at the presentation, “never has the sun exhibited
his disc above the horizon of Dessau without being confronted
by Schwabe’s imperturbable telescope; and that appears to have
happened on an average about 300 days a-year. So, supposing that
he had observed but once a-day, he has made 9000 observations,
in the course of which he discovered about 4700 groups. This is,
I believe, an instance of devoted persistence unsurpassed in
the annals of astronomy. The energy of one man has revealed a
phenomenon that had eluded the suspicion of astronomers for 200
years.”
HAS THE MOON AN ATMOSPHERE?
The Moon possesses neither Sea nor Atmosphere of appreciable
extent. Still, as a negative, in such case, is relative only to
the capabilities of the instruments employed, the search for the
indications of a lunar atmosphere has been renewed with fresh
augmentation of telescopic power. Of such indications, the most
delicate, perhaps, are those afforded by the occultation of a planet
by the moon. The occultation of Jupiter, which took place on January
2, 1857, was observed with this reference, and is said to have
exhibited no _hesitation_, or change of form or brightness, such as
would be produced by the refraction or absorption of an atmosphere. As
respects the sea, if water existed on the moon’s surface, the sun’s
light reflected from it should be completely polarised at a certain
elongation of the moon from the sun; and no traces of such light have
been observed.
MM. Baer and Maedler conclude that the moon is not entirely without
an atmosphere, but, owing to the smallness of her mass, she is
incapacitated from holding an extensive covering of gas; and they add,
“it is possible that this weak envelope may sometimes, through local
causes, in some measure dim or condense itself.” But if any atmosphere
exists on our satellite, it must be, as Laplace says, more attenuated
than what is termed a vacuum in an air-pump.
Mr. Hopkins thinks that if there be any lunar atmosphere, it must
be very rare in comparison with the terrestrial atmosphere, and
inappreciable to the kind of observation by which it has been tested;
yet the absence of any refraction of the light of the stars during
occultation is a very refined test. Mr. Nasmyth observes that “the
sudden disappearance of the stars behind the moon, without any change
or diminution of her brilliancy, is one of the most beautiful phenomena
that can be witnessed.”
Sir John Herschel observes: The fact of the moon turning always the
same face towards the earth is, in all probability, the result of an
elongation of its figure in the direction of a line joining the centres
of both the bodies, acting conjointly with a non-coincidence of its
centre of gravity with its centre of symmetry.
If to this we add the supposition that the substance of the moon is
not homogeneous, and that some considerable preponderance of weight
is placed excentrically in it, it will be easily apprehended that the
portion of its surface nearer to that heavier portion of its solid
content, under all the circumstances of the moon’s rotation, will
permanently occupy the situation most remote from the earth.
In what regards its assumption of a definite level, air obeys
precisely the same hydrostatical laws as water. The lunar
atmosphere would rest upon the lunar ocean, and form in its basin a
lake of air, whose upper portions at an altitude such as we are now
contemplating would be of excessive tenuity, especially should the
provision of air be less abundant in proportion than our own. It by
no means follows, then, from the absence of visible indications of
water or air on this side of the moon, that the other is equally
destitute of them, and equally unfitted for maintaining animal or
vegetable life. Some slight approach to such a state of things
actually obtains on the earth itself. Nearly all the land is
collected in one of its hemispheres, and much the larger portion
of the sea in the opposite. There is evidently an excess of heavy
material vertically beneath the middle of the Pacific; while not
very remote from the point of the globe diametrically opposite
rises the great table-land of India and the Himalaya chain, on the
summits of which the air has not more than a third of the density
it has on the sea-level, and from which animated existence is for
ever excluded.--_Herschel’s Outlines_, 5th edit.
LIGHT OF THE MOON.
The actual illumination of the lunar surface is not much superior to
that of weathered sandstone-rock in full sunshine. Sir John Herschel
has frequently compared the moon setting behind the gray perpendicular
façade of the Table Mountain at the Cape of Good Hope, illuminated
by the sun just risen from the opposite quarter of the horizon, when
it has been scarcely distinguishable in brightness from the rock in
contact with it. The sun and moon being nearly at equal altitudes, and
the atmosphere perfectly free from cloud or vapour, its effect is alike
on both luminaries.
HEAT OF MOONLIGHT.
M. Zantedeschi has proved, by a long series of experiments in the
Botanic Gardens at Venice, Florence, and Padua, that, contrary to the
general opinion, the diffused rays of moonlight have an influence
upon the organs of plants, as the Sensitive Plant and the _Desmodium
gyrans_. The influence was feeble compared with that of the sun; but
the action is left beyond further question.
Melloni has proved that the rays of the Moon give out a slight degree
of Heat (see _Things not generally Known_, p. 7); and Professor Piazzi
Smyth, from a point of the Peak of Teneriffe 8840 feet above the
sea-level, has found distinctly perceptible the heat radiated from the
moon, which has been so often sought for in vain in a lower region.
SCENERY OF THE MOON.
By means of the telescope, mountain-peaks are distinguished in the
ash-gray light of the larger spots and isolated brightly-shining points
of the moon, even when the disc is already more than half illuminated.
Lambert and Schroter have shown that the extremely variable intensity
of the ash-gray light of the moon depends upon the greater or less
degree of reflection of the sunlight which falls upon the earth,
according as it is reflected from continuous continental masses, full
of sandy deserts, grassy steppes, tropical forests, and barren rocky
ground, or from large ocean surfaces. Lambert made the remarkable
observation (14th of February 1774) of a change of the ash-coloured
moonlight into an olive-green colour bordering upon yellow. “The moon,
which then stood vertically over the Atlantic Ocean, received upon its
right side the green terrestria
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