Great Facts
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Title: Great Facts
Author: Frederick C. Bakewell
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*** START OF THE PROJECT GUTENBERG EBOOK GREAT FACTS ***
Transcribers' Note: Greek transliterations were added by the
transcribers and enclosed in {curly braces.}
GREAT FACTS.
[Illustration: THE "GREAT EASTERN" STEAMSHIP, LAUNCHED 1858.]
GREAT FACTS:
A
POPULAR HISTORY AND DESCRIPTION
OF THE MOST
REMARKABLE INVENTIONS
DURING THE PRESENT CENTURY.
BY
FREDERICK C. BAKEWELL,
AUTHOR OF
"PHILOSOPHICAL CONVERSATIONS," "MANUAL OF ELECTRICITY," ETC.
ILLUSTRATED WITH NUMEROUS ENGRAVINGS.
NEW YORK:
D. APPLETON AND COMPANY,
346 & 348 BROADWAY.
1860.
PREFACE.
The conveniences, the comforts, and luxuries conferred on Society by
the many important Inventions of the present century, must naturally
excite a desire to know the origin and progress of the application of
scientific principles, by which such advantages have been gained.
Practically considered, those Inventions are of much greater value
than the discoveries of Science on which most of them depend; and the
scientific inquirer who confines his views to abstract principles,
without looking beyond them to the varied methods of their application
to useful purposes, may be compared to a traveller who, having toiled
arduously to gain the top of a mountain, then shuts his eyes on the
prospect that lies before him.
To the inquiring youth, more particularly, it is desirable that he
should be enabled to satisfy his wish to know by what means such
wonders as Steam Navigation, Locomotion on Railways, the Electric
Telegraph, and Photography have been gradually developed; and in
becoming acquainted with the successive steps by which they have
advanced towards their present perfection, he will at the same time
learn a useful lesson of perseverance under difficulties, and will have
his mind impressed with many valuable scientific truths. The knowledge
to be gained by such inquiry is eminently practical, and of a kind
which those engaged in any of the pursuits of life can scarcely fail to
require.
A History of Inventions almost necessarily implies a description of
the mechanisms and processes by which they are effected; so far, at
least, as to render the principles on which their actions depend
understood. It would be impossible, however, in a work of this limited
size to enter minutely into explanations of mechanisms, and into the
applications of scientific discoveries, which would require a separate
treatise for each; but it has been the Author's endeavour to give a
succinct, intelligible account, free from technicalities, of the manner
in which they operate, so as to be comprehensible to all classes of
readers.
By thus giving a popular character to the work, to make it acceptable
to the young, it is hoped that it will not be found less worthy, on
that account, the perusal of those more advanced in life.
When Beckman wrote his History of Inventions, towards the close
of last century, scarcely any of the wonderful discoveries and
contrivances that now form parts of our social system were known;
and the table of contents of his two large volumes affords a curious
insight to the nature and limited extent of such contrivances as were
then considered most important. The introduction into his history
of such subjects as canary birds, carp, the adulteration of wine,
apothecaries, cock-fighting, and juggling, lead us to infer that the
Historian of Inventions at that time must have had some difficulty to
find appropriate matter wherewith to fill his volumes. The opposite
difficulty now presents itself. The numerous important, wonderful,
and curious accomplishments of human skill and ingenuity during the
present century render preference perplexing, where so many deserve
description. From among the number that press for notice, the Author
has endeavoured to select those that are either the most important, the
most remarkable, or that seem to possess the germs of future progress;
and he trusts that the selection he has made, and the mode in which the
subjects have been treated, will render this volume interesting and
instructive.
F. C. B.
_6 Haverstock Terrace, Hampstead,
November, 1858._
CONTENTS.
PAGE
THE PROGRESS OF INVENTION 1
STEAM NAVIGATION 6
STEAM CARRIAGES AND RAILWAYS 32
THE AIR ENGINE 60
PHOTOGRAPHY 67
DISSOLVING VIEWS 86
THE KALEIDOSCOPE 92
THE MAGIC DISC 98
THE DIORAMA 103
THE STEREOSCOPE 112
THE ELECTRIC TELEGRAPH 124
ELECTRO-MAGNETIC CLOCKS 172
ELECTRO-METALLURGY 179
GAS LIGHTING 188
THE ELECTRIC LIGHT 209
INSTANTANEOUS LIGHTS 214
PAPER MAKING MACHINERY 221
PRINTING MACHINES 230
LITHOGRAPHY 249
AERATED WATERS 258
REVOLVERS AND MINIÉ RIFLES 266
CENTRIFUGAL PUMPS 275
TUBULAR BRIDGES 282
SELF-ACTING ENGINES, INCLUDING THE NASMYTH STEAM HAMMER 295
GREAT FACTS.
THE PROGRESS OF INVENTION.
The inventive faculty of man tends more directly than any other
intellectual power he possesses to raise him in the scale of creation
above the brutes. Nearly every advance he makes beyond the exercise of
his natural instincts is caused by invention--by that power of the mind
which combines known properties in different ways to obtain new results.
When an Indian clothes himself with the skins of animals, and when
he collects the dried leaves of the forest for his bed, he is either
an original inventor, or he is profiting by the inventions of
others. Those simple contrivances--the first steps in the progress
of invention--are succeeded by the more labored efforts of inventive
genius, such as contriving means of shelter from rain, or from
the heat of the sun, when caves cannot be found to creep into, or
the overhanging foliage fails to afford sufficient covering. The
construction of places of shelter is an imitation of the protection
formed by Nature; and the rudest hut and the most magnificent palaces
have their prototypes in caverns and in the interlacing branches of
trees.
Nature also supplies knowledge of the means by which inventors are
enabled to work. The savage who seizes hold of a broken bough is
in possession of the _lever_, the uses of which he learns by the
facility it affords in moving other objects. He ascends to the top of
a precipice by walking up the sloping hill behind, and he thus becomes
practically acquainted with the principle of the _inclined plane_.
The elements of all the mechanical powers are then at his command, to
be applied by degrees in administering to his wants, as his inventive
faculties, guided by observation and experience, suggest. An accidental
kick against a loose stone shows the action of propulsive force; and
the stone that he has struck with his foot, he learns to throw with his
hand. The bending of the boughs of trees to and fro by the wind teaches
the action of springs; and in the course of time the bow is bent by a
strip of hide, and the relaxation of the spring, after farther bending,
propels the arrow. Observation and imitation thus lead to invention,
and every new invention forms the foundation of further progress.
It has been so with every invention at present known, and must so
continue to the end of time:--"There is nothing new under the sun." Gas
lighting, Steam locomotion, and the Electric Telegraph have each sprung
from some source "old as the hills," though so modified by gradually
progressive changes, that the giant we now see bears no resemblance to
the infant of ages past.
The observation that light particles floating in the air are attracted
by amber when rubbed, which was made known six centuries before the
Christian era, was the origin of the invention by which communications
are now transmitted, with the rapidity of lightning, from one part of
the world to another. There is no apparent relation between effects
so dissimilar; yet the steps of progress can be distinctly traced,
from the attraction of a feather to the development of the electric
telegraph.
Whenever the history of an invention can be thus tracked backward to
its source, it will be found to have advanced to its present state by
progressive steps, each additional advance having been dependent on
the help given by the progress before made. Sometimes these onward
movements are greater and more remarkable than others, and the persons
who made them have become distinguished for their inventive genius,
and are considered the benefactors of mankind; yet they were but the
followers of those who had gone before and shown the way.
Many of the most remarkable inventions are attributable to accidents
noted by observing and inventive minds. Not unfrequently also have
important discoveries of truth been made in endeavouring to establish
error; and new light is being constantly thrown on the path of
invention by unsuccessful experiments.
This view of the means by which inventions originate and are brought
to perfection may appear to detract from the merit of inventors, since
it regards them as founding their conceptions altogether on the works
of others, or on chance. But instead of diminishing their claims to
approbation and reward, it places those claims on a more substantial
foundation than that of abstract original ideas. The man who has the
faculty to perceive that by a different application of well-known
principles he can produce useful effects before unknown, directly
benefits mankind far more than the discoverer of the principles which
had till then lain dormant; and the numerous difficulties which ever
arise before an invention can be practically operative, frequently
afford exercise for reasoning powers of the highest kind, which may
develop new arrangements, that exhibit as much originality and research
as were displayed by the discoverers of the principles on which the
invention depends.
The dependence of every invention on preceding ones produces very
frequently conflicting claims among inventors, who, forgetting how
much they were indebted to others, do not hesitate to charge those,
who make still further improvements, with imitation and piracy. It is,
indeed, sometimes difficult to determine whether the alterations made
in well-known contrivances are, or are not, of sufficient importance
to constitute inventions; and there can be no doubt that there is too
great facility afforded, by the indiscriminate grant of letters patent,
for the establishment of monopolies that often serve to obstruct
further improvements. At the same time, it must be observed that a
very trifling addition or change occasionally gives practical value to
an invention, which had been useless without it. In such cases, though
the individual merit of the inventor is small, the benefit conferred
may be important, and may operate influentially in promoting the
progress of civilization.
Scientific discovery goes hand in hand with invention, and they
mutually assist each other's progress. Every discovery in science
may be applicable to some new purpose, or give greater efficiency to
what is old. Those new and improved instruments and processes provide
science with the means of extending its researches into other fields of
discovery; and thus, as every truth revealed, supplies inventive genius
with fresh matter to mould into new forms, those creations become in
their turn agents in promoting further discoveries.
The action and reaction thus constantly at work, tend to give
accelerating impulse to invention, and are continually enlarging its
sphere of operations. Instead, therefore, of supposing, as some do,
that invention and discovery have nearly reached their limits, there is
more reason to infer that they are only at the commencement of their
careers; and that, great as have been the wonders accomplished by the
applications of science during the first half of the present century,
they will be at least equalled, if not surpassed, by those to be
achieved before its close.
STEAM NAVIGATION.
Ships, propelled by some mysterious power against wind and against
tide, cutting their ways through the water without apparent impulse
and like things of life, were not unfrequently seen gliding along in
the regions of fancy, ages before the realization of such objects on
geographical seas and rivers was looked upon as in the slightest degree
possible. Even at the beginning of the present century, it seemed to
be more probable that man would be able to navigate the air at will,
than that he should be able, without wind or current, and in opposition
to both, to propel and steer large ships over the waves; yet, within
twenty years afterwards, Steam Navigation had ceased to be a wonder.
If we look back into the records of past ages, we find that inventive
genius was active in the earliest times, in endeavouring to find other
means of propelling boats than by manual labour and the uncertain wind,
some of which contrivances point to the method subsequently adopted by
the constructors of steam-vessels.
To enable us to appreciate properly the gradual advances that have
been made in perfecting any invention, it is necessary to consider its
distinguishing features, and the difficulties which inventors have had
successively to contend against. On taking this view of the progress
of Steam Navigation, it will be found that the amount of novelty to
which each inventor has a claim is very small, and that his principal
merit consists in the application of other inventions to accomplish
his special object. The same remark will indeed apply to most other
inventions; for the utmost that inventive genius can accomplish, is to
put together in new forms, and with different applications, preceding
contrivances and discoveries, which were also the results of antecedent
knowledge, labour, and skill.
When, for instance, we look upon an ordinary steam-boat, the most
remarkable and the most important feature is the paddle-wheel, by the
action of which against the water the boat is propelled. Yet that
method of propelling boats was practised by the Egyptians hundreds of
years before steam power was thought of; and the ancient Romans made
use of similar wheels, worked by hand, as substitutes for oars. It
would seem, therefore, to be only a small step in inventive progress,
after the discovery of the steam engine, to apply that motive power to
turn the paddle-wheels which had been previously used; and now that we
see the perfected invention, it may surprise those who are unacquainted
with the difficulties which attend any new appliance, that Steam
Navigation did not sooner become an accomplished fact.
In a book called "Inventions and Devices," by William Bourne, published
in 1578, it was proposed to make a boat go by paddle-wheels, "to be
turned by some provision." The Marquis of Worcester, in his "Century
of Inventions," also speaks vaguely of a mode of propelling ships. But
Capt. Savery, the inventor of the earliest working steam engine, was
the first to suggest the application of steam to navigation; and Dr.
Papin, who contended with Savery for priority of the invention, also
suggested about the same time the application of the elastic force of
steam to that purpose.
These crude notions, however, do not deserve to be considered as
inventions, though they probably assisted in suggesting the idea of
the plan proposed by Mr. Jonathan Hulls, who in 1736 took out a patent
for a steam-boat, and in the following year published a description of
his invention, illustrated by a drawing, entitled, "A description and
draught of a new-invented machine for carrying vessels or ships out
of or into any harbour, port, or river, against wind or tide, or in a
calm."
The greater part of this publication is occupied with answers to
objections that he supposed might be raised to the scheme, and in the
preface he makes the following observations on the treatment inventors
were exposed to in his day, which we fear will apply equally at the
present time. "There is," he says, "one great hardship lies too
commonly on those who purpose to advance some new though useful scheme
for the public benefit. The world abounding more in rash censure than
in candid and unprejudiced estimation of things, if a person does not
answer their expectations in every point, instead of friendly treatment
for his good intentions, he too often meets with ridicule and contempt."
[Illustration]
At the time of Mr. Hulls' invention, Watt had not made his improvements
in the steam engine, and the kind of engine Hulls employed was similar
to Newcomen's, in which the steam was condensed in the cylinder,
and the piston, after being forced down by the direct pressure of
the atmosphere, was drawn upwards again by a weight. The paddle, or
"vanes," as he called them, were placed at the stern, between two
wheels, which were turned by ropes passing over their peripheries.
The alternate motion of the piston was ingeniously converted into a
continuous rotary movement, by connection with other ropes attached to
the piston and to the weight, the backward movement being prevented by
a catch or click.
The woodcut which lays before you is a reduced copy of Hulls'
"draught" of his steam-boat, as given in his book, a copy of which is
preserved in the British Museum.
The utmost application of steam power to navigation contemplated by
Hulls was to tow large vessels into or out of harbour, in calm weather,
by means of a separate steam tug-boat, as he considered the cumbersome
mechanism would be found objectionable on board the ships to be thus
propelled. It does not appear that this plan was effectually tried,
nor was the arrangement of the mechanism, nor the imperfect condition
of the steam engine at that period, calculated to make the effort
successful.
For some years after Mr. Hulls' plan had been published, and had
proved abortive, no further attempt seems to have been made, until the
improvements in the steam engine, by Watt, rendered it more applicable
for the purpose of navigation. The French claim for the Marquis de
Jouffroy the honour of having been the first who successfully applied
steam power to propel boats, in 1782; though another French nobleman,
the Comte d'Auxiron, and M. Perier, had eight years previously made
some experiments with steam-boats on the Seine. The Marquis de
Jouffroy's steam-boat, which was 145 feet long, was tried on the Soane,
near Lyons, with good promise of success. The marquis was, however,
obliged to leave France by the fury of the Revolution, and when he
returned in 1796, he found that a patent had been granted to M. le
Blanc, for building steam-boats in France. He protested against the
monopoly, but the patent remained in force, and the plan received
no further development, either from the Marquis de Jouffroy, or the
patentee.
About five years later, Mr. Patrick Miller, of Dalswinton, in Scotland,
directed his attention to the propulsion of boats by mechanical means,
and contrived different kinds of paddles, and other propellers to be
worked by hand, which were tried on boats on Dalswinton Lake. The
great labour required to work these machines induced Mr. James Taylor,
a tutor in Mr. Miller's family, to suggest the use of steam power to
turn them, and he recommended Mr. Miller to obtain the assistance of
William Symington, an engineer, who was at that time endeavouring to
make a steam locomotive carriage. Among the first difficulties that
suggested themselves, was the danger of setting fire to the boat by
the engine furnace. This difficulty was overcome by Mr. Taylor, and
the arrangements were completed, and the experiment was tried in 1788.
The steam engine and mechanism were applied to a double pleasure-boat;
the engine being placed on one side, the boiler on the other, and the
paddle-wheel in the centre. The cylinders of the steam engine were only
four inches in diameter; but with this engine the boat was propelled
across Dalswinton Lake at a speed of five miles an hour.
The success of this experiment induced Mr. Miller to have a larger
boat built, expressly adapted for the introduction of a steam engine.
It was constructed under the superintendence of Symington, and was
tried successfully on the Forth and Clyde Canal in 1789, when it was
propelled at the rate of seven miles an hour.
In the arrangement of the mechanism of this boat, the cylinder was
placed horizontally, for the purpose of making connection between the
paddle-wheel and the piston, without the working beam. The piston was
supported in its position by friction wheels, and communicated motion
to the paddles by a crank. The paddles were placed in the middle of the
boat, near the stern; and there was a double rudder, connected together
by rods which were moved by a winch at the head of the vessel.
It is not very clear why Mr. Miller did not follow up this success.
Objection, indeed, was made by the proprietors of the canal on account
of the agitation of the water, which it was feared would injure
the banks. It would appear also that a misunderstanding took place
between Miller and Symington, which gave the former a distaste to the
undertaking; and having shown that such a plan was practicable, he left
others to carry it into practical effect.
Several methods of propelling boats, otherwise than by paddles, had
some years previously been suggested; among which were two that have
been again and again tried by succeeding inventors, down to the present
day.
One of these is an imitation of the duck's foot, which expands when it
strikes the water, and collapses when it is withdrawn. The other is
the ejection of a stream of water at the stern, or on both sides of
the boat, so as to produce a forward movement by reaction. Both these
plans of propulsion seem feasible in design; but they have hitherto
failed in practice. A pastor at Berne, named J. A. Genevois, has the
credit of having invented the duck-feet propeller in 1755; and in 1795,
six years after Mr. Miller's successful experiments, Earl Stanhope had
a steam-boat built on that principle. It was so far a failure, that it
was not propelled faster than three miles an hour. The other method of
propulsion, though of older date, was patented in 1800 by Mr. Linnaker,
who proposed to draw the water in at the head of the vessel, and eject
it at the stern, and thus to obtain a double action on the water for
propelling; but the plan was not found to answer.
In 1801, Lord Dundas revived Mr. Miller's project, and availed himself
of Mr. Symington's increased experience and the further improvements in
the steam engine, to construct a much more perfect steam-boat than any
that had been made. He spent £3,000 in the experiments, and in March,
1802, his vessel, called the "Charlotte Dundas," was tried on the same
scene of action, the Forth and Clyde Canal. This boat, according to
Symington's report, towed two vessels, each of seventy tons burthen, a
distance of nineteen miles and a half in six hours, against a strong
wind. The threatened injury to the banks of the canal by the great
agitation of the water prevented the use of this boat, which was
consequently laid aside; for the views of the inventors of steam-boats
in the first instance were limited to their employment to drag boats
along canals.
We now approach a period when more decided advances and more rapid
progress were made towards realizing steam navigation as a practical
fact. Mr. Fulton, an American, residing in France, after making a
number of experiments, under the sanction and with the assistance of
Mr. Livingstone, the American Ambassador, launched a small steam-boat
on the Seine in 1803, but the weight of the engine proved too great for
the strength of the boat, which broke in the middle, and immediately
went to the bottom.
Not disheartened by this failure he built another one, longer and
stronger, and this he succeeded in propelling by steam power, though
very slowly. It was, indeed, a much less successful effort than the
attempts of Mr. Miller and Lord Dundas. Having been threatened with
opposition by M. le Blanc, the patentee of steam-boats in France,
Fulton determined to return to his native country, where the large
navigable rivers and lakes offered ample scope for the development of
steam navigation. Having heard of the success of Symington's boats,
he visited Scotland for the purpose of profiting by his experience;
and he induced Symington, by promises of great advantages if the
invention succeeded in America, to show him the "Charlotte Dundas" at
work, and to enter into full explanations of every part. Thus primed
with the facts, and with the further suggestions of Symington, Fulton
repaired to New York. Mr. Livingstone, who had assisted Fulton in his
experiments, was himself an inventor of several plans of propelling
vessels by steam, and in 1798 he obtained a patent in the State of
New York, for twenty years, on condition that he should produce a
steam-boat by the 7th of March, 1799, that would go at the rate of
_four_ miles an hour. Having failed to fulfil that condition, the
patent privilege was left open, and was promised to the first inventor
who succeeded in propelling a boat by steam power at the proposed
speed of four miles an hour. Fulton, who had entered into partnership
with Mr. Livingstone, possessed advantages in the construction of the
vessel he built in America, far greater than any previous inventor. He
had not only gained knowledge by his former failures, but he was able
to profit by the experience of others, and he had secured a superior
steam engine, manufactured by Boulton and Watt, of twenty-horse power.
This was a much more powerful engine than any that had been used in
any former experiment; the one employed by Mr. Livingstone having had
only five-horse power. This steam-vessel was launched at New York in
1807, and was called the "Clermont," the name of Mr. Livingstone's
residence on the banks of the Hudson. Its length was 133 feet, depth 7
feet, and breadth 18 feet. The boiler was 20 feet long, 7 feet deep,
and 8 feet broad. There was only one steam cylinder, which was 2 feet
in diameter, with a length of stroke of 4 feet. The paddle-wheels were
15 feet in diameter, and 5 feet broad; and the burthen of the vessel
was 160 tons. Crowds of spectators assembled to see the boat start on
its first experimental voyage. The general impression, even of those
who were friendly to Fulton, was that it would fail, and an accident
which occurred when the vessel was under way confirmed this opinion.
The foreboders of evil exclaimed immediately that they had "foreseen
something of the kind;" and observed "it was a pity so much expense
had been incurred for nothing!" The required repairs were, however,
soon made. The vessel when again tried cut her way bravely through
the water, to the astonishment of all, and the doubts, and fears, and
lamentations were quickly changed into congratulations.
As the "Clermont" urged its way up the Hudson, its chimney emitting
innumerable sparks from the dried pine wood used as fuel, it excited
great alarm among those who were not prepared for such an apparition.
An American paper of that day thus described the effect produced on
the crews of other ships in the river:--"Notwithstanding the wind and
tide were adverse to its approach, they saw with astonishment that
it was rapidly coming towards them; and when it came so near that
the noise of the machinery and paddles was heard, the crews, in some
instances, shrunk beneath their decks from the terrific sight, or left
their vessels to go on shore; whilst others prostrated themselves and
besought Providence to protect them from the approach of the horrible
monster which was marching on the waves, and lighting its path by the
fires which it vomited."
During the time that Fulton was building his steam-boat Mr. R. L.
Stevens, of Hoboken, in the State of New Jersey, was also engaged in a
similar undertaking. Though his name is comparatively little heard of
in the history of Steam Navigation, his efforts were more successful
than any that had been made previously, and but for the fortunate
chance to Fulton that he was able to launch and put his boat in action
a few days before Stevens had completed his, all, and more than all,
the merit that is now ascribed to the former would have been attributed
to Stevens. The previous successful experiment of Fulton having
fulfilled the conditions imposed by the State of New York, he obtained
the exclusive right of steam navigation on the rivers and along the
coast of that State; therefore, after Stevens had launched his boat on
the Hudson, he was unable to employ it there. In this predicament he
ventured on the hazardous experiment of taking his steam-vessel by sea,
and successfully accomplished his voyage from New York to Delaware.
This was the first attempt to put to sea in a steam-boat.
Mr. Stevens introduced many important improvements. He increased the
length of stroke of the engines; he applied upright guides for the
piston-rod, to supply the place of the parallel motion; and he divided
the paddle-wheel by boards, by which means a more uniform motion was
obtained. By these improvements he succeeded in raising the speed of
steam-vessels to thirteen miles an hour.
Whilst Steam Navigation was making such progress in America, it was not
neglected in this country. Mr. Henry Bell, of Glasgow, a man of great
ingenuity, had for some time directed his attention to the subject,
and had given some useful hints to Fulton. Seeing, as he afterwards
said, no reason why others should profit by his plans without his
participation in the fame and the profits, he determined to build a
steam-boat himself, which was completed and launched in 1811. Bell
called his boat the "Comet," in commemoration of the remarkable
eccentric luminary which was at that time frightening Europe from
its propriety. The boat was 25 tons burthen, with an engine of about
3-horse power. It plied on the Frith of Forth for a distance of 27
miles, which in ordinary weather it accomplished in 3½ hours. The
"Comet" is generally supposed to have been the first steam-boat that
plied regularly in Europe; and its construction was so perfect, that
no boat built for many years afterwards surpassed it, taking into
consideration its size and the small power of its engine. Bell, though
he had done so much to advance Steam Navigation in this country, was
allowed to suffer neglect and penury in his old age, till the town of
Glasgow granted him a small annuity for his services.
A claim has been preferred on behalf of Messrs. Furnace and Ashton, of
Hull, to priority in building the first steam-vessel that was worked
in England. It is stated, that "about the year 1787, experiments were
made on the river Hull, by Furnace and Ashton, on the propulsion
of vessels by steam power. Furnace and Ashton built a boat, which
plied on the river, between Hull and Beverley, for some time, and
answered exceedingly well. In consequence of the good results of their
experiments, they built a much larger vessel and engine, and sent the
whole to London, to be put together and finished; after which it was
subjected to the severest tests, and gave the greatest satisfaction.
The vessel was bought by the Prince Regent (afterwards George IV.),
who had it fitted and furnished as a pleasure yacht; but it was soon
afterwards burnt, having, it is supposed, been wilfully set on fire
by persons who were afraid that such an invention would be injurious
to their calling. The Prince was so much pleased with the invention
and ingenuity of Furnace and Ashton, that he granted them a pension
for their lives of £70 a year each."[1] This steamer was on the
paddle-wheel principle, propelled by a steam engine, to which was
attached a copper boiler.
From this time forward the progress of Steam Navigation was very
rapid. Steam-ships were built longer and larger, and with more
powerful engines; and the most skilful builders rivalled each other
in the construction and adaptation of their vessels and engines, so
as to attain the highest possible speed. The locality in which Steam
Navigation may be said to have had its birth continued for a long time
to be pre-eminent, and steam-boats built on the Clyde still rank very
high, if not the highest, in the scale of excellence.
The ordinary land steam engine required considerable alterations to
adapt it to marine purposes; nor was it till great experience had been
gained in propelling vessels by steam power, that the more essentially
requisite modifications were adopted. It was found important, in the
first place, to reduce the space occupied by the machinery as much as
possible. The boilers were consequently made of less dimensions, but
more extensive in their heating surface. It was also found desirable
to employ two engines instead of one, the pistons being made to rise
and descend alternately. By this means the motion was rendered more
equable, and by placing the cranks of the common shaft at right angles,
the "dead points" were passed more readily, and the want of a fly wheel
was thus compensated.
The steam-boats employed in this country were, almost from the first,
and continue with few exceptions to be, on the low-pressure condensing
principle; the whole of the machinery being placed below the deck. This
renders it necessary to diminish the height of the engines as much
as possible; and in all marine steam engines, till within the last
twenty years, instead of having a working beam over the cylinders,
a cross-head was placed at the top of the piston-rod, the action of
which was conveyed by parallel motions to cross beams on each side,
which were situated at the bottom part of each engine. The motion,
compared with that of an ordinary land engine, was thus inverted. The
proportions of the cylinders were also different; the length of stroke
being shorter, to diminish the height, and the diameter consequently
greater. The valves, and the gearing connected with them, the air pump,
the condenser, and other subsidiary parts, do not differ essentially
from those of land engines; but the governor is omitted, as it is found
impracticable to work a marine engine with great regularity.
Latterly, many engineers have introduced, with much success,
arrangements for communicating the action directly from the piston-rod
to the crank, without the intervention of the beam and parallel
motions. This is generally done by causing the piston-rod to work
between guides, and a jointed arm connects it with the crank. One
method of producing the same effect is to make the cylinders oscillate
on pivots, as contrived by Mr. Murdoch, in the first model steam
carriage, made in 1784. This principle has been successfully carried
into operation by Messrs. Penn, of Greenwich. The oscillating cylinders
accommodate themselves to the varying directions of the cranks, and
the strain occasioned by guide rods is diminished; but when very large
cylinders are required, the friction and the pressure on the pivots
must tend to counterbalance the advantage otherwise obtained.
In the ordinary paddle-wheel steam-boats, the floats of the
paddle-wheels are fixed at equal distances round the rim, radiating
from the centre; therefore they enter and come out of the water
obliquely. There is, consequently, a considerable loss of power
attending the use of such paddle-wheels, as only one float at a time
can be acting vertically on the water, and exerting the propelling
force in a direct line. Several attempts have been made to remedy this
defect, and to produce what is called "feathering" floats, every one
of which will act against the water at right angles. The mechanism
required for making this adjustment is, however, liable to get out
of order, and the introduction of vertically acting floats has
consequently been very limited.
The large projecting paddle-boxes are objectionable in sea-going
ships, as they present so large a surface to the action of the wind,
and either impede the course of the ship, or make it unweatherly.
This inconvenience was experienced in the early progress of Steam
Navigation, and many attempts were made to overcome it, by substituting
a different kind of propeller. Recourse was had to the inventions of
the ancients, from whom the paddle-wheel was taken, to find some other
means of propulsion. A method of propulsion, similar in principle to
the action of sculls at the back of a boat, had been contrived long
before the inconvenience of paddle-wheels in Steam Navigation was
experienced. In 1784, Mr. Bramah obtained a patent for a propeller
similar in its forms to the vanes of a windmill, which by acting
obliquely on the water as it revolved, pushed the boat forward. Ten
years afterwards, an "aquatic propeller" was patented by Mr. William
Lyttleton, a merchant in London. It consisted of a single convolution
of a three-threaded screw, and may be considered to be the first screw
propeller invented. Numerous other ingenious persons, among whom were
Tredgold, Trevethick, Maceroni, and Millington, afterwards invented
propellers on the screw principle; but none of them were sufficiently
satisfactory in their results to come into practical use.
In 1836, Mr. Smith and Mr. Ericsson obtained a patent for a screw
propeller, which nearly resembled Mr. Lyttleton's original contrivance;
and by perseverance in struggling against the many obstacles with
which he had to contend, Mr. Smith succeeded, though all previous
efforts had failed. His partner, however, became disheartened by the
obstacles thrown in their way, and left this country for America before
the success of the screw was established.
The first ship fitted with the screw propeller was called the
"Archimedes." It was a vessel of 237 tons burthen, with a draught of
water of 9 feet 4 inches. The screw projected at the stern, and being
turned rapidly round by the steam engine, the oblique action of the
thread of the screw against the water impelled the vessel forward.
The "Archimedes" was originally fitted with a single-threaded screw,
the threads of which were 8 feet apart, and there were two convolutions
of the screw round the shaft. One convolution of the screw having
been accidentally broken off, the ship was found to go faster in
consequence; and, following the course of investigation suggested by
the accident, Mr. Smith at last adopted a double-threaded screw, with
only half a convolution. The average performance of the engines was 26
strokes per minute, and the number of revolutions of the screw in the
same time was 138½. The "pitch" of the screw was 8 feet; that is, the
space across one entire convolution of the thread would have measured
8 feet; consequently, had it been acting against a solid body, as a
cork-screw when entering a cork, one revolution of the shaft would have
advanced the vessel 8 feet, and the speed would have been 12½ miles an
hour; but the utmost speed the "Archimedes" obtained was 9¼ nautical
miles. The difference was owing to the screw "slipping" in the water,
because the fluid yielded to the oblique action of the blades.
[Illustration]
The results of the working of that experimental ship were so
satisfactory, that other ships were soon built, with modifications
of the form of the propeller. It was found disadvantageous to have
an entire convolution of the thread of the screw; for one part of it
worked in the wake of the other, and resistance was produced by the
backwater. After numerous experiments, in which the dimensions of the
screw were successively diminished, the propeller was at length reduced
to two oblique blades. Experiments on a large scale were conducted by
Captain Carpenter, to determine the size and angle of inclination best
adapted for the purpose of propulsion; and nearly all the ships now
built for the Royal Navy are fitted with propellers on his principle.
The annexed diagram represents on a scale of one-eighth of an inch to a
foot, the form of the propeller of the "Agamemnon," of 606-horse power,
which was recently engaged in successfully laying down the Atlantic
Telegraph cable. The diameter of the screw is 18 feet, and the pitch 20
feet.
The screw propeller possesses great advantages in ships of war, as
it is not exposed to damage by shot, and it leaves the entire deck
clear for mounting guns. It has also the further advantage of not
interfering with the working of sails, and is, therefore, admirably
adapted for sea-going ships that economize fuel by alternately steaming
and sailing, as the wind is adverse or favourable. The commotion in
the water made by paddle-wheels, which is an objection to their use in
narrow rivers, is avoided by screw propellers, which being immersed
under the water, make little agitation on the surface, and the ships
move along without any apparent impelling power.
The speed of ships with the best constructed screw propellers is fully
equal to that of paddle-wheel vessels; and when two vessels of the same
size, and with engines of equal power, one fitted with paddles, and the
other with the screw, are fastened stem and stern together, in a trial
of strength, the screw propeller has been found to have the advantage,
and to pull its antagonist along at the rate of one or two miles an
hour.
The difficulty at first experienced in the application of the screw
propeller was to communicate a sufficiently rapid motion to the shaft
to which it is fixed; but, by the employment of direct-acting engines,
this difficulty has been for the most part overcome. The power is
generally first applied to drive a large cog-wheel, the teeth of which
take into the teeth of a smaller cog-wheel fixed to the propeller
shaft, and in this manner the velocity is sufficiently increased.
In 1852 the proportion of screw to paddle-wheel vessels building
in the Clyde was as 43 to 30. The advantages of the propeller are
becoming every year more appreciated, and it is rapidly superseding the
paddle-wheel.
In the steam-boats of the United States the engines are constructed on
the high-pressure principle; and by working with steam of the pressure
of 100 pounds on the square inch, and with larger paddle-wheels, their
boats attain a speed exceeding sixteen miles an hour. But numerous
explosions of boilers on the North American rivers have operated
as a caution against the introduction of high-pressure engines in
steam-boats in this country. The dread of high-pressure steam was early
impressed by the destructive explosion of the boiler of a steam-vessel
at Norwich in 1817, which led to a long parliamentary inquiry into
the subject; and the subsequent loss of life by the explosion of the
"Cricket" on the Thames, has tended to strengthen the apprehension
of high-pressure steam engines. For river use, however, when fresh
water is always at command for generating the steam, there appears to
be no more cause for fear of high-pressure engines in boats than on
railways, provided the boilers are constructed with sufficient care.
The experiments made by Mr. Fairbairn on the strength of boilers,
the results of which were communicated at the meeting of the British
Association in 1853, prove, that by increasing the number and strength
of the "stays," or internal supports, of the boilers, they may be made,
if sufficiently strong, to resist any possible pressure; and that the
square shape, which was supposed to be the weakest, offers, on the
contrary, peculiar facilities for giving increased strength. In one
of these experiments made to determine the ultimate strength of the
flat surfaces of boilers, when divided into squares of sixteen inches
area, the boiler did not give way until it had sustained the enormous
pressure of 1,625 pounds on the square inch.
It might be desirable, in the construction of steam boilers, to adopt
the same principle that is introduced in the building of gunpowder
mills, one-half of which is built in strong masonry, whilst the other
is made of wood. By this means, when an explosion does occur, much
less damage is done, for the lighter part only is blown away, which
does little injury. In the same manner, steam engine boilers might
be constructed with a small portion comparatively weaker, so that if
it gave way there would not be much damage done. Safety-valves are
intended to act in that manner; and if they were properly constructed,
they would sufficiently answer the purpose, and guard against the
possibility of danger; but the numerous accidents that occur with
boilers provided with imperfect safety-valves, show that there is
a necessity for some more effectual protection. Engineers are not
sufficiently alive to the importance of improvements in this respect.
They supply an engine with safety-valves, which would answer the
purpose if kept in proper condition; but they do not make effectual
provision against careless management and reckless misconduct. Some
years since, a gentleman in America sent to the author a description,
with drawings, of a safety-valve that combined the principles of the
safety-plug without its inconvenience; it being so contrived that
when the boiler became too hot, it melted some fusible metal which
previously held down the valve, and then a weight pulled it open to
allow an ample escape of steam; but when the heat was lowered, the
valve again closed. This was shown to an eminent engineer for his
opinion. He pronounced it to be very ingenious, and that it would, no
doubt, answer the purpose; but he said, "_An improved safety-valve is
not wanted_, those in use being quite sufficient for the purpose."
In steam-ships, where salt water is used for generating the steam, the
incrustation on the sides of the boilers becomes a serious annoyance.
It obstructs the communication of heat from the furnace to the water,
and the metal is thus liable to become red-hot. Numerous plans have
been adopted for the purpose of preventing the accumulation of salt
on the sides of the boiler, the most common of which is to allow the
water, when saturated with saline matter, to escape, and then to fill
the boiler afresh. Among other contrivances for effecting the same
purpose, without the waste of heating power which the change of
water occasions, is Mr. Hall's plan of condensing the steam in dry
condensers, cooled externally, so that the distilled water may be used
again and again. This plan though theoretically good, is not much
adopted; for the condensation of steam cannot be so well accomplished
by that means as when a jet of cold water is thrown directly into the
condenser. The principle of the dry condenser has, however, been lately
made available in a new kind of engine, wherein the combined action of
steam and of spirit vapour is applied as the propelling power.
Steam-boats had been for many years in extensive use on the rivers and
seas of Europe and America before it was thought practicable to make
voyages in them across the Atlantic. At the meeting of the British
Association at Liverpool in 1837, that subject was brought forward for
consideration, and it was then attempted to be shown, by calculations
of the quantities of coal requisite for such a voyage, that steam
communication with America would not be profitable, if it could be
accomplished, as the coal would occupy so much of the tonnage as to
leave scarcely any space for passengers and goods. Within a few months
afterwards those calculations were set at nought by the "Sirius" and
the "Great Western," which successfully crossed the Atlantic with
passengers and cargo, the former in nineteen days from Cork, and the
latter in sixteen. At the present time, steam-packets are constantly
crossing from New York to Liverpool in eleven days.
Steam-ships now find their way to India and even to Australia, though
the necessity of taking in coals at depôts supplied from England
not only prolongs the time, but adds so materially to the cost, as
to render steam communication with those distant places scarcely
practicable with profit, since no freight can pay for the expense of
coaling under such circumstances. To overcome that difficulty, it
was proposed to build ships large enough to carry a supply of coals
sufficient for the voyage there and back. One of those ships has
been built for the Eastern Steam Navigation Company by Mr. J. Scott
Russell, from the plans of Mr. Brunel, which is 675 feet long, 83 feet
broad, and 60 feet deep. It is adapted to carry 6,000 tons burthen,
in addition to the engines and requisite quantity of fuel, and to
accommodate 2,000 passengers. This monster ship has been built on what
is called the "wave principle" of ship-building, with long concave
bows. It is to be propelled by the combined powers of the paddle-wheel
and the screw. The engines for the former consist of 4 oscillating
cylinders, 16 feet long and 74 inches in diameter, and the screw is
to be worked by 4 separate engines, with cylinders of 84 inches in
diameter. The speed which the "Great Eastern" is estimated to attain
is 24 miles an hour, and it is calculated that the voyage to Australia
will be accomplished in 30 days. There seems, at present, but small
prospect of those calculations being realized, for the great cost
incurred in launching the vessel and other expenses have exhausted the
funds of the company by whom the ship was constructed.
Another company has, however, been formed for the purpose of
completing, if possible, this great experiment in Steam Navigation;
and the opinion so strongly expressed by Mr. Fairbairn at the recent
meeting of the British Association at Leeds, of the strength of the
monster ship, will give additional stimulus to their exertions. The
ship is built on the same principle of construction as the Britannia
Bridge over the Menai Straits, and it was stated by Mr. Fairbairn that
it might be supported out of water, either in the centre or at each
end, without injury.
STEAM CARRIAGES AND RAILWAYS.
No invention of the present century has produced so great a social
change as Steam Locomotion on railways. Not only have places that were
formerly more than a day's journey from each other been made accessible
in a few hours, but the cost of travelling has been so much reduced,
that the expense has in a great degree ceased to operate as a bar to
communication by railway for business or pleasure.
Though the coaching system in this country had attained the highest
degree of perfection, a journey from London to Liverpool, previously
to the formation of railways, was considered a serious undertaking.
The "fast coach," which left London at one o'clock in the day, did not
profess to arrive in Liverpool till six o'clock the following evening,
and sometimes it did not reach there till ten o'clock at night; and the
fare inside was four guineas, besides fees to coachmen and guards. The
same distance is now performed in six hours, at one-third the expense,
and at one-fourth the fatigue and inconvenience.
Railway Locomotion, however, forms no exception to the rule, that
most modern inventions have their prototypes in the contrivances
of ages past. They were used upwards of two hundred years before
locomotive engines were known, or before the steam engine itself was
invented. The manifest advantage of an even track for the wheels
long ago suggested the idea of laying down wood and other hard,
smooth surfaces for carriages to run upon. They were first applied
to facilitate the traffic of the heavily laden waggons from the coal
pits; the "tramways," as they were called, being formed of timber
about six inches square and six feet long, fixed to transverse timbers
or "sleepers," which were laid on the road. These original railways
were made sufficiently wide for the wheels of the waggons to run upon
without slipping off; the plan of having edgings to the rails, or
flanges to the wheels, not having been adopted till a later period.
To protect the wood from wearing away, broad plates of iron were
afterwards fixed on the tramways.
Cast iron plate rails were first used in 1767. The flat plates on which
the wheels ran were made about three inches wide, with edges two inches
high, cast on the near side, to keep the wheels of the "trams" on the
tracks. These iron plates were usually cast in lengths of six feet, and
they were secured to transverse wooden sleepers by spikes and oaken
pegs. The tramways were laid down on the surface of the country without
much regard to hills and valleys, the horses that drew the trains being
whipped to extra exertion when they came to a hill, and in descending
some of the steep inclines, the animals were removed, and the loaded
waggons were allowed to descend the hills by their own gravity, the
velocity being checked by a break put on by a man who accompanied them.
The chief use of the tramways was to facilitate the conveyance of
coals from the pits to the boats; and as the level of the pit's
mouth was higher than that of the water, it was an object, in laying
down a tramway, to make a continuous descent, if possible, for the
loaded trains to run down, the dragging back of the empty ones being
comparatively easy. Thus, though "engineering difficulties" were
not much considered in the construction of those early railways,
engineering contrivances were adopted to diminish the draught, by
making the gradients incline in one direction.
Soon after the invention of the Steam Engine had been practically
applied to mining purposes, its power was directed to draw the coal
waggons on railways. This was done about the year 1808; and, in
the first instance, the application of steam power was limited to
drawing the loaded waggons up steep inclines. A stationary engine was
erected at the top of the incline, and the waggons were drawn up by a
rope wound round a large drum. This mode of traction was afterwards
extended, in many instances, along the whole railway, so as to
supersede the use of horse power. The employment of stationary engines
in this manner was continued, even after the invention of locomotive
steam engines, to draw the trains up inclines that were too steep for
the power of the small locomotives at first used to surmount; nor has
this plan been yet altogether abandoned.
The application of steam to the direct propulsion of carriages was
a comparatively slow process. It was, indeed, contemplated by Watt,
as a substitute for horse power on common roads, though he does not
seem to have contrived any means by which it might be done. The first
known application of the kind was made by Mr. Murdoch, an engineer in
the employment of Messrs. Boulton and Watt, who in 1784 constructed a
working model of a steam carriage, still preserved, and which formed
one of the most interesting objects in the Great Exhibition of 1851.
The boiler of this model locomotive is made of a short length of brass
tube, closed with flat ends. The furnace to generate the steam consists
of a spirit lamp. The steam is conducted directly from the boiler to a
single cylinder, which is mounted on a pivot near the centre, so that
by the movement of the cylinder the piston-rod may adapt itself to the
varying positions of the crank. The two hind wheels are fixed to the
axle, and on the latter is the crank, attached to the piston-rod. A
single wheel in front serves to guide the carriage, which is propelled
by the rotation of the two hind wheels. The elastic force of the steam
is directly applied as the moving power; and after it has done its work
in the cylinder, it is allowed to escape into the air.
This first known application of steam as a locomotive power is more
perfect in its general arrangements than many steam carriages that
were subsequently brought into operation; and in the plan of balancing
the cylinder on pivots, we perceive the origin of the oscillating
engines, which have been recently introduced with much success in Steam
Navigation. By that arrangement there is attained the most direct
application of the piston-rod to the crank, with the least loss of
power.
Mr. Murdoch's intention was to employ such carriages on common roads,
but he did not proceed to put his plan into operation. Several other
engineers, among whom was Symington--who, as we have before seen,
took an active part in the invention of Steam Navigation--afterwards
endeavoured to realize Mr. Murdoch's ideas on a working scale; but the
first who succeeded in making a locomotive engine, that ran with any
success, were Messrs. Trevethick and Vivian. In 1804 they constructed a
locomotive engine, which was employed on a mineral railway at Merthyr
Tydvil, in South Wales. The boiler of their engine resembled the one
in Mr. Murdoch's model, in having circular flat ends; but, to increase
the heating surface, a flue was introduced in the middle of the boiler,
which passed through it and back again, in the shape of the letter
U. The lower part of the tube formed the furnace, and the upper part
returned through the boiler into the chimney. The steam was admitted
into and escaped from the cylinder by the working of a four-way cock,
the contrivance of the slide-valve being then unknown. On the axle of
the crank a cog-wheel was fixed, and, by means of the usual gearing, it
communicated motion to the hind wheels, which were fixed to the axle,
so that when the wheels revolved the carriage was propelled.
It is a remarkable fact that this engine of Mr. Trevethick's presents
the first practical application of high-pressure steam as a motive
power. Watt had, indeed, suggested the application of the impulsive
power of steam, and Mr. Murdoch's model locomotive was necessarily
constructed on that principle; but until Mr. Trevethick's locomotive
engine was in action, no application of high-pressure steam had been
made on a working scale.
The projectors of locomotive engines were for many years possessed with
the notion that it was necessary to have some contrivance to prevent
the wheels from slipping on the road, as it was supposed that otherwise
the wheels would be turned without moving the carriage. Numerous plans
were devised for overcoming this imaginary difficulty; and though
experience proved that even on railways the adhesion of the wheels was,
in ordinary circumstances, sufficient, yet various schemes continued
to be tried for the purpose of facilitating the ascent of hills.
The imitation of the action of horses' hoofs was one of the means
attempted, but such additional aids were eventually found to be of no
avail, and were discontinued.
All the endeavours that were made, in the first instance, to apply
steam power to locomotion, had in view the propulsion of carriages
on common roads, the idea of constructing level railways through the
country, for facilitating the general traffic, being looked upon as
too visionary a project to be realized. The inventors of locomotive
engines consequently directed their attention almost exclusively to the
arrangement that would best apply steam power to overcome the varying
obstacles and undulations of common roads.
It is very curious and interesting, in tracing the progress of an
invention, to observe the different phases through which it has passed,
before it has been brought into the state in which it is ultimately
applied. It not unfrequently happens that the original purpose sinks
into insignificance, and is almost lost sight of, as the invention
becomes more fully developed. Other objects, that were not perceived,
or were considered altogether impracticable, present themselves, and
are then pursued; and the invention, when perfected, is very different
from its original design. Thus the endeavours of the first inventors of
Steam Navigation were confined to the construction of steam-tugs that
would propel the boats along canals, or take a ship into harbour, the
notion of fitting a steam engine into a ship to propel it across the
sea not having been thought of. In the same manner, the invention of
Steam locomotion on railways was either not contemplated in the first
instance, or was considered very subordinate to the construction of
carriages to be propelled by steam power on common roads.
Among the most successful of those engineers, who constructed steam
carriages to run on roads, were Mr. Gurney, Mr. Birstall, Mr.
Trevethick, Mr. Handcock, and Colonel Maceroni. Mr. Gurney was one of
the first on the road. His steam carriage completed several journeys
very successfully, and proved the practicability of employing steam
power in locomotive engines many years before the first passenger
railway was brought into operation. This, like all other new
inventions, was, however, beset with difficulties, among which the
most annoying was the determined obstruction the plan met with from
the trustees of public roads, who levied heavy tolls on the carriages,
and laid loose stones on the roads to stop them from running, as the
driving wheels were found to be destructive to the roads. There was
also considerable danger in running steam carriages on the same roads
on which ordinary traffic was conducted, because the strange appearance
of the engines, their noise, and the issuing steam, frightened the
horses.
Notwithstanding these difficulties, the importance of applying steam
as a locomotive power for passenger traffic became so apparent, that a
Committee of the House of Commons was appointed in 1831, to consider
whether the plan could be adopted with safety on common roads, and
whether it should not be encouraged by passing an Act of Parliament for
regulating the tolls chargeable on such carriages, and for preventing
the obstructions to which they had been exposed. The evidence given
before the Committee was greatly in favor of steam carriages, and
tended to show that there was no insuperable difficulty to the general
adoption of them. The Committee accordingly reported as follows:--
"Sufficient evidence has been adduced to convince your Committee--
"1st. That carriages can be propelled by steam on common roads at an
average speed of ten miles an hour.
"2nd. That at that rate they have conveyed upwards fourteen passengers.
"3rd. That their weight, including engines, fuel, water, and
attendants, may be under three tons.
"4th. That they can ascend and descend hills of considerable elevation,
with facility and safety.
"5th. That they are perfectly safe for passengers.
"6th. That they are not (or need not be, if properly constructed)
nuisances to the public.
"7th. That they will become a speedier and cheaper mode of conveyance
than carriages drawn by horses.
"8th. That as they admit of greater breadth of tire than other
carriages, and as the roads are not acted upon so injuriously as by the
feet of horses in common draught, such carriages will cause less wear
of roads than coaches drawn by horses.
"9th. That rates of toll have been imposed on steam carriages which
would prohibit them being used on several lines of roads, were such
charges permitted to remain unaltered."
In defiance of this favourable report, experience proved that there
were defects in that system of locomotion greater than its advocates
were disposed to admit, and that the mechanism was frequently broken
or disarranged by the constant jarring caused by the roughness of
the road. The alarm of the horses drawing other carriages was also
calculated to produce fearful accidents.
So far, indeed, as regarded the power of locomotion, the steam
carriages were successful. The author was witness of this success
during a short excursion in Colonel Maceroni's carriage, which ascended
hills and ran over rough roads with great ease, and at a speed of
twelve miles an hour. The practical difficulties, however, were so
great, that steam carriages have not been able to compete with horse
power; for the original cost of the boiler and engine, the necessary
repairs, and the expense of fuel, amounted to more than the cost and
keep of horses. The plan was practically tried for several weeks, in
1831, by running a steam carriage for hire from Paddington to the Bank
of England. The carriage, of which the annexed diagram is an outline,
was one of those constructed by Mr. Handcock. The engine was placed
behind the carriage, which was capable of containing sixteen persons,
besides the engineer and guide. The latter was seated in front, and
guided the carriage by means of a handle, which turned the fore wheels.
The carriage was under perfect control, and could be turned within
the space of four yards. With this carriage, Mr. Handcock stated he
accomplished one mile up hill at the rate of seventeen miles an hour.
The carriage loaded very well at fares which would now be considered
exorbitant, but the frequent necessity for repairs rendered the
enterprise unsuccessful, and the steam carriage was taken off the road.
[Illustration]
The successful establishment of railways, and the great advantages
arising from them compared with the ordinary means of conveyance,
still further reduced the chance of establishing Steam Locomotion
on roads, and the plan is now in abeyance, at least, if it has not
been abandoned. It is very possible, however, that in the progress of
invention, modifications may be made in the steam engine, to adapt it
more successfully to the purpose; or more suitable motive powers may be
discovered, that may bring mechanical locomotion on roads again into
favour.
The successful application of Steam Locomotion on railways cannot be
dated more than thirty years ago; yet in that short period its progress
has been so rapid, that but few traces of the old mode of travelling by
stage coaches are now to be seen.
Some locomotive steam carriages had, indeed, been introduced on the
Stockton and Darlington coal railway, by Mr. George Stephenson, in
1825, but their results were not so satisfactory as to induce the
extension of the plan to the other railways that were then laid down
in the coal districts of England. The cylinders of those engines were
vertical, and each of the four wheels acted propulsively on the rails
by means of an endless chain running along cog-wheels fixed on the
axles. The utmost speed that could be obtained by this means was eight
miles an hour; and so little were these engines calculated to solve
the problem of the practicability of steam locomotive engines, that
when the first passenger railway was projected, from Liverpool to
Manchester, it was proposed to propel the carriages by the traction
of ropes, put in motion by stationary steam engines. The directors,
before finally determining on the system of locomotion to be adopted,
offered a premium of £500 for the best locomotive engine to run on that
line. The stipulations proposed, and the conditions which the required
engines were to fulfil, may be regarded as a curious exposition of the
limited views then taken of the capabilities of Steam Locomotion on
railways. The engine "was to consume its own smoke; to be capable of
drawing three times its own weight at 10 miles an hour, with a pressure
on the boiler not exceeding 50 pounds on the square inch; the whole to
be proved to bear three times its working pressure--a pressure guage
to be provided; to have two safety-valves, one locked up; the engine
and boiler to be supported on springs, and rested on six wheels, if
the weight should exceed 4½ tons; height to the top of the chimney not
to exceed 15 feet; weight, including water in boiler, not to exceed 6
tons, or less, if possible; the cost of the engine not to exceed £550."
An engine, called the "Rocket," constructed by Messrs. Booth and
Stephenson, was the successful competitor for the prize. It so far
exceeded the required conditions as to speed, that, when unattached to
any carriages, it ran at the rate of 30 miles an hour. The principal
cause of its successful action was the introduction of a boiler
perforated lengthwise by many tubes, through which the heated air of
the furnace passed to the chimney, and by this means a much larger
evaporating surface was obtained than in the boilers previously
employed, with a single flue passing through the centre. The tubes were
of copper, three inches in diameter, one end of each communicating with
the chimney, and the other with the furnace. There were twenty-five of
these tubes passing through the boiler, and fixed water-tight at each
end.
The boiler was 3 feet 4 inches in diameter, and 6 feet long; and it
exposed a heating surface of 117 square feet. There were two cylinders,
placed in a diagonal position, with a stroke of 16½ inches, and each
worked a wheel 4 feet 8½ inches diameter, the piston-rod being attached
externally to spokes of the driving wheels. The draught of the chimney,
aided by the escaping steam from the cylinders, which was admitted into
it, served to keep the fuel in active combustion. The "Rocket" weighed
41 tons; the tender, with water and coke, 3 tons 4 cwt.; and two loaded
carriages attached, 9½ tons; so that the engine and train together
weighed about 19 tons. The boiler evaporated 114 gallons of water in
the hour, and consumed, in the same time, 217 pounds of coke. The
average velocity of the train was 14½ miles per hour.
The accompanying woodcuts represent an elevation of the "Rocket,"
and a section of its boiler. In these figures, _a_ is the fire-box
or furnace, surrounded on all sides with water, with the exception
of the side perforated for the reception of the tubes; _b_ is the
boiler; _d_, one of the steam cylinders; _e_, the chimney; _h_ and _i_,
safety-valves; _f_, one of the connecting rods for communicating motion
to the driving wheels.
[Illustration]
Three other engines competed with the "Rocket," two of which had
attained great speed on previous trials. These were the "Novelty,"
constructed by Messrs. Braithwaite and Ericsson, which weighed only
2¾ tons; and the "Sans Pareil," manufactured by Mr. Arkworth, which
weighed 4½ tons. On the day of trial, the 6th of October, 1829, these
two locomotive engines were disabled by the bursting of some of their
pipes, and thus the field was left clear to the "Rocket," for the
fourth engine had no chance of winning the prize.
The "Rocket," indeed, more than fulfilled all the conditions required
by the directors of the railway, who thereupon decided on employing
locomotive engines for the traffic on the line.
The "Rocket" has formed the model on which all subsequent locomotive
engines have been constructed; for, though numerous alterations and
improvements have been made in details, and though the size of the
engines has been greatly enlarged, the principle of construction
remains essentially the same. Among the improvements that have been
introduced by different inventors, is an increase in the number of
the tubes in the boiler, so as to facilitate the generation of steam,
some of the engines now made having upwards of 100 tubes, though of
smaller diameter than those of the "Rocket." The boilers have also been
elongated, to enlarge the evaporating surface and economize fuel. The
cylinders are placed horizontally, and they are generally fixed inside
the boiler, to prevent the cooling of the steam. The piston-rods are
attached to cranks on the axle, placed at right angles to each other;
and the engines are generally mounted on six wheels, four of which are
driving wheels, made of larger size than the two others, and they are
coupled together by connecting arms. The large and powerful engines on
the Great Western Railway have, however, only two driving wheels, which
are 8 feet in diameter. These engines weigh as much as 31 tons, which
is seven times more than the weight of the "Rocket." They are capable
of taking a passenger train of 120 tons at an average speed of 60
miles an hour on easy gradients; and the effective power, as measured
by a dynamometer, is stated to be equal to 743 horses.
The accompanying engraving of one of the recently constructed engines
on the Great Western Railway presents a remarkable difference in
point of size and general arrangement to the original prototype, from
which, however, it does not materially differ in the principle of its
construction.
[Illustration]
The complete success of the "Rocket" having settled the question of the
mode of traction, the Directors of the Liverpool and Manchester Railway
made increased efforts to complete the line, and to open it for general
traffic. In September, 1830, all was ready for the opening, which it
was determined should take place with a ceremony indicative of the
importance of the great event. The principal members of the Government
consented to take part in the inauguration of the railway, and the
utmost interest was excited throughout the country for the success of
an undertaking that promised to be the commencement of a new era in
travelling. The 15th of September was the day appointed, and there
were eight locomotive engines provided to propel the same number of
trains of carriages, which were to form the procession. All along the
line there were crowds of persons collected to witness the ceremony.
The trains started from the Liverpool end of the railway; and, as they
passed along, they were greeted by the cheers of the astonished and
delighted spectators. On arriving at Parkside, seventeen miles from
Liverpool, the engines stopped to take in fresh supplies of fuel and
water. The passengers alighted and walked upon the line, congratulating
one another on the delightful treat they were enjoying, and on the
success of the great experiment. All hearts were bounding with joyous
excitement, when a disastrous event occurred, which threw a deep gloom
over the scene. The Duke of Wellington, Sir Robert Peel, and Mr.
Huskisson were among those who were walking on the railway, when one of
the engines was recklessly put in action, and propelled along the line.
There was a general rush to the carriages, and Mr. Huskisson, in trying
to enter his carriage, slipped backwards and fell upon the rails. The
wheels of the engine passed over his leg and thigh, and he was so
severely injured, that he expired in a few hours.
Notwithstanding this lamentable occurrence, the journey was continued
to Manchester, and the carriages returned to Liverpool the same
evening. On the following morning the regular trains commenced running,
and they were crowded with passengers, nothing daunted by the fatal
calamity on the opening day.
The immense advantages of this mode of travelling were at once
apparent, and lines of railway in different parts of the country
were quickly projected. The railway from London to Birmingham was
the first one commenced after the completion of the Liverpool and
Manchester line, and a connecting link with Manchester and Liverpool
was also begun by a separate company. The Birmingham Railway was opened
throughout on the 17th September, 1838.
Railway enterprise was not checked by the great cost of the
undertakings, nor by the miscalculations of the engineers, who, in the
first instance, frequently greatly under-estimated the expenditure
requisite for the cuttings, embankments and tunnels, which were thought
necessary to attain as perfect a level as possible. The original
estimate for the Liverpool and Manchester Railway was £300,000, but
the amount expended on the works at the time of opening was nearly
£800,000. The original estimate of the London and Birmingham Railway,
including the purchase of land, and the locomotives and carriages,
was £2,500,000, whilst the actual cost amounted to £5,600,000, the
cost of the works and stations being about £38,000 per mile. The Grand
Junction Railway, from Birmingham to Liverpool, was more economically
constructed, because the difficulties to be surmounted were not so
great, and less attention was paid to maintain a level line. It was
estimated to cost, including all charges, £13,300 per mile, though the
actual cost was £23,200.
The plan adopted for laying down and fixing the rails on all the
railways in England, with the exception of the Great Western, is
nearly similar to that on which the original coal-pit railways were
constructed. Pieces of timber, called "sleepers," are laid at short
distances across the road, and on to these sleepers are fixed cast iron
"chairs," into which the rails are fastened by wedges, the sleepers
being afterwards covered with gravel or other similar material, called
"ballast," to make the timbers lie solidly, and to keep the road dry.
The railway system of Great Britain was commenced without sufficient
attention to the determination of the best width apart of the rails.
In forming the Liverpool and Manchester Railway, the guage of the
railways in the collieries was adopted, and the width between the rails
was made 4 feet 8½ inches. The same width of rails was adopted on the
London and Birmingham and Grand Junction Railways; and as uniformity of
guage was essential to enable the engines and carriages on one line to
travel on another, the other railways connected with the grand trunk
line were made of the same width of guage. Mr. Brunel, the engineer
of the Great Western Railway, departed from that uniformity, and laid
down the rails 7 feet apart. The increased width of guage possesses
many advantages, of which greater steadiness of motion and greater
attainable speed, without risk, are the most important; but, at the
same time, the additional space incurs a greater expense in laying out
the line. As branches from the Great Western Railway spread into the
districts where the narrow guage railways had been laid down, much
inconvenience has arisen from the break of guage, as it occasions the
necessity for a change of carriages. On some railways, to avoid this
inconvenience, narrow and broad guage rails have been laid down on the
same line.
If the railway system of Great Britain were to be recommenced, after
the experience that has now been acquired, the medium guage would most
probably be adopted; and in commencing to lay down railways in Ireland,
the Irish Railway Commissioners recommended 6 feet 2 inches as the most
desirable width, and that standard has been advantageously adopted in
the sister country.
Travelling experience tells greatly in favour of the broad gauge. There
is no railway out of London whereon the carriages run so smoothly, and
on which the passengers are so conveniently accommodated, as on the
Great Western. The speed attained on that railway also surpasses that
on any other. The express train runs from London to Bristol, a distance
of 120 miles, in less than three hours. The author accompanied an
experimental train, when one of the large engines was first put upon
the line, and during some portion of the journey a rate of 70 miles an
hour was accomplished without any inconvenient oscillation.
It must be observed, with regard to the action of locomotive engines,
that as the piston-rods are attached directly to cranks on the axle,
each piston makes a double stroke for every revolution of the driving
wheels; consequently, when the engine is running at great speed, the
movement of the piston is so rapid, that there is neither time for
the free emission of the waste steam, nor for the full action of the
high-pressure steam admitted. There is, therefore, a great waste of
power occasioned by the admitted steam having to act against the steam
that is escaping; and an engine, calculated to have the power of 700
horses, will not exert a tractive force nearly equal to that amount.
With a driving wheel 6 feet in diameter, a locomotive engine will be
propelled 18 feet by each double stroke of the piston, if there be no
slipping on the rails; consequently, in the space of a mile, the piston
must make 300 double strokes. When running, therefore, at the speed of
30 miles an hour, the piston makes 150 double strokes per minute.
The success of the great experimental railway from Manchester to
Liverpool not only stimulated similar works in this country, undertaken
by private enterprise; but the Continental Governments quickly
perceived the importance of that means of communication, and commenced
the formation of railways at the national cost, and placed them under
governmental control. Belgium was peculiarly adapted, by the general
level state of the country, for the formation of railways; and long
before any connected system was completed in this country, the _chemins
de fer_ formed a complete net-work in that kingdom, and the system of
conducting the traffic was brought to a much higher state of perfection
than was attained in this country. The rate of travelling, however, was
slower.
It is a question that has been often mooted, whether it is better
to allow the system of communication throughout the country to be
conducted by independent companies of enterprising individuals, or
to place it entirely under the control of the Government. The want
of system manifested in the formation of the railways in England
has proved a serious inconvenience, and has occasioned wasteful
expenditure, besides having led to a fearful destruction of life,
owing to the want of careful attention to the means of safety, and to
ill-judged parsimony in the management of the traffic. There can be
no doubt that if the Government had undertaken the work zealously,
and with the view of establishing a complete system of railway
communication, many of the inconveniences now experienced might have
been avoided, and the railways might have been laid down and worked
at considerably less cost, and with a large addition to the national
revenue. There is, however, so strong a disinclination in this country
to the centralization of Government power, and to the extension of
Government influence, that the people generally had rather submit
to considerable inconvenience and expense, than tolerate the system
of railway management which has been adopted on the Continent. The
necessity of interference, to protect the interests of the public, has
nevertheless compelled the Government, though late, to adopt measures
for controlling the management of the railway companies, and stringent
regulations are now imposed with a view to prevent unnecessary danger
to railway passengers.
The railway system of Great Britain, though established entirely by
private enterprise, represents an amount of capital equal to one-third
of the national debt, and nearly 100,000 individuals are directly
employed in conducting the traffic on the various railways in this
kingdom. An idea of the vastness of these undertakings, and the
important interests involved in them, may be formed from the following
facts, stated by Mr. Robert Stephenson, at the Institution of Civil
Engineers:--
"The railways of Great Britain and Ireland, completed at the beginning
of 1856, extended 8,054 miles, and more than enough of single rails
were laid to make a belt round the globe. The cost of constructing
these railways had been £286,000,000. The working stock comprised 5,000
locomotive engines and 150,000 carriages and trucks; and the coal
consumed annually by the engines amounted to 2,000,000 tons, so that
in every minute 4 tons of coal flashed into steam 20 tons of water.
In 1854 there were 111 millions of passengers conveyed on railways,
each passenger travelling an average of 12 miles. The receipts during
1854 amounted to £20,215,000; and there was no instance on record in
which the receipts of a railway had not been of continuous growth,
even where portions of the traffic had been abstracted by new lines.
The wear and tear of the railways was, at the same time, enormous. For
instance, 20,000 tons of iron rails required to be annually replaced,
and 26 millions of wooden sleepers perished in the same time. To supply
this number of sleepers, 300,000 trees were felled, the growth of which
would require little less than 5,000 acres of forest land. The cost of
running was about fifteen pence per mile, and an average train will
carry 200 passengers. Without railways, the penny post could not have
been established, because the old mail coaches would have been unable
to carry the mass of letters and newspapers that are now transmitted.
Every Friday night, when the weekly papers are published, eight or ten
carts are required for Post Office bags on the North-Western Railway
alone, and would hence require 14 or 15 mail coaches."
Adverting to other advantages derived from railway locomotion, Mr.
Stephenson noticed the comparative safety of that mode of travelling.
Railway accidents occurred to passengers in the first half of 1854 in
the proportion of only one accident to every 7,194,343 travellers.
As regards the saving of time, he estimated that on every journey,
averaging 12 miles in length, an hour was saved to 111 millions of
passengers per annum, which was equal to 38,000 years, reckoning eight
working hours per day; and allowing each man an average of 3s. a day
for his work, the saving of time might be valued at £2,000,000 a year.
There were 90,000 persons employed directly, and 40,000 collaterally,
on railways; and 130,000 men, with their families, represent 500,000 so
that 1 in 50 of the entire population of the kingdom might be said to
be dependent for their subsistence on railways.
Every year adds to the extent of the railway system, and to the
increase of the traffic, so that considerable addition should be made
to the amounts stated by Mr. Stephenson to represent the state of
railway enterprise and railway traffic at the present day. The traffic
returns for the week ending the 25th of September, 1858, amounted
to £502,720; and the gross receipts of the railways in 1857 were
£24,174,610. The railways now open for traffic in England, Scotland,
and Ireland extended to upwards of 9,000 miles, and the lines reported
to be in the course of construction amount to one-ninth the length of
those completed.
In estimating the importance and advantage of railway travelling, there
must not be omitted its cheapness and comfort, compared with travelling
by stage coach. There are some persons, indeed, who look back with
regret to the old coaching days; and it must be admitted that railways
have taken away nearly all the romance of travelling, and much of the
exhilarating pleasure that was experienced when passing through a
beautiful country on the top of a well-horsed coach in fine weather.
The many incidents and adventures that gave variety to the journey were
pleasant enough for a short distance; but two days and a night on the
top of a coach, exposed to cold and rain, or cramped up inside, with
no room to stir the body or the legs, was accompanied with an amount of
suffering which those who have experienced it would willingly exchange
for a seat, even in a third-class railway carriage. In a national and
in a social point of view, also, railways have produced important
improvements. They tend to equalize the value of land throughout the
kingdom, by bringing distant sources of supply nearer the points of
consumption; they have given extraordinary stimulus to manufacturing
industry; and by connecting all parts of the country more closely
together, railway communication has concentrated the energies of the
people, and has thus added materially to their wealth, their comforts,
and to social intercourse.
Nor must we, in noticing the grand invention of locomotion on
railways, omit to mention some of the many subsidiary works which
have been created during its progress towards perfection, and which
have contributed to its success. Tunnels, of a size never before
contemplated, have penetrated for miles through hard rocks, or through
shifting clays and sands; embankments and viaducts have been raised
and erected, on a scale of magnitude that surpasses any former similar
works; bridges of various novel kinds, invented and constructed for
the special occasions, carry the railways over straits of the sea,
through gigantic tubes; across rivers, suspended from rods supported by
ingeniously devised piers and girders; and over slanting roads, on iron
beams or on brick arches built askew. As to the locomotive engines,
though the principle of construction remains the same, the numerous
patents that have been obtained attest that invention has been active
in introducing various improvements in the details of construction,
to facilitate their working, and to increase their power. The various
plans that have been contrived for improving the structure of the
wheels and axles, for the application of breaks, for deadening the
effect of collisions, for making signals, for the forms of the rails,
and for the modes of fastening them to the road, are far too many to be
enumerated.
In addition to the innumerable contrivances that have been invented
for the improvement of the working of ordinary railways, several
distinct systems of railway locomotion have been introduced to public
notice, some of which seemed very feasible, though they have nearly
all gradually disappeared. Of these, the Atmospheric railway was the
most promising, and for a time it bid fair to supersede the use of
locomotive engines. The propulsion of the carriages, by the pressure
of the atmosphere acting on an attached piston working in a vacuum
tube, possessed many theoretical advantages, and if it could be
applied economically, railway travelling would become more pleasant
and more free from danger than it is. On several lines of railway the
atmospheric plan was put into operation, but owing to the expense of
working, it was gradually abandoned. The short line from Kingston to
Dalky, in Ireland, up a steep incline, was favourable to the working of
the atmospheric railway, and there it continued to linger for some time
after it had been abandoned elsewhere.
It is to be regretted that the atmospheric railway should have failed
in economical working, for it possessed greater advantages for general
traffic than the ordinary locomotive railway trains; and it is probable
that if the same amount of inventive power and industry, which have
been bestowed in improving locomotive engines, had been directed to
overcome the difficulties of atmospheric traction, it might have proved
economically successful.
The facility of travelling by railway has excited a spirit of
locomotion before undreamed of. Instead of the diminished demand for
horses which was apprehended when railways displaced stage coaches,
public conveyances have increased a hundredfold. We can now scarcely
conceive the time when there was not an omnibus in the streets of
London, yet, scarcely more than thirty years ago, they were unknown,
and travelling by stage carriages from one part of the town to another
was prohibited by law! On their first introduction, omnibuses were
considered absurdities, and were ridiculed as "painted hearses." The
present omnibus traffic in London alone amounts to nearly £20,000 per
week.
THE AIR ENGINE.
Numerous attempts have been made to supersede steam as a motive power,
with the view to avoid the loss of heat by its absorption in the steam
in a latent state. Mercury vapour and spirit vapour have been tried,
in the expectation that as they possess much less capacity for heat,
an equal pressure might be obtained, with a diminished loss of heating
power. Several gaseous agents have been applied to the same purpose, of
which carbonic acid gas seemed to present the best prospect of success,
because it becomes expanded with a comparatively small increase of
temperature. None of these attempts to produce a motive power superior
to steam have yet proved successful. They have all, after a short
season of promise, dropped out of notice; and the only one that is
still in the field, struggling for superiority, is the air engine.
The first known air engine was invented by Sir George Cayley, in 1803.
In his engine the air was heated by passing directly through the hot
coals of the furnace, which some engineers yet consider to be the best
mode of expansion; but its operation did not answer expectations. Mr.
D. Stirling, of Dundee, afterwards improved on Sir George Cayley's
plan, and introduced a method of regaining the heat from the expanded
air, after it had done its work in the cylinder, and of applying it to
expand the air again. Engines on this construction have been for some
years working in Scotland, and in 1850 Mr. Stirling took out a patent
for an improvement in the arrangement, which is stated to have been
very successful.
Though Sir George Cayley and Mr. Stirling were the first in the field
as inventors of air engines, the name of Mr. Ericsson, an American,
is more closely associated with the invention, as he has for many
years been conducting experiments on a large scale, and has tried his
"caloric engine" on land, and on a ship of large burthen, built for the
purpose.
The principle and the working of Mr. Ericsson's caloric engine is
nearly the same as Mr. Stirling's; but as it has been brought most
prominently into notice, we shall direct attention more particularly
to its construction and performances. Mr. Ericsson obtained a patent
for his caloric engine in this country in 1833, and a subsequent patent
for improvements on it was taken out in 1851. During those years, and
to a late period, he was indefatigably working out the principle, and
numerous highly favourable reports have from time to time been made of
the results of the experiments; but the advantages to be derived from
the air engine remain nevertheless very questionable.
The object attempted to be gained is to make the same heating power
do its work again and again. Atmospheric air, after being expanded by
passing over an extensive hot surface, exerts the force thus acquired
to raise the piston of a large cylinder, and it is then attempted
to abstract the heat as the air issues out, and to apply it to the
expansion of a further quantity.
The practicability of this plan has undergone much discussion; its
friends and foes being equally confident in their opinions. The
former pronounce it to be one of the most valuable inventions of
the age, being calculated to economize heat, and to give greatly
additional impulse to navigation; whilst its opponents declare that the
calculations are erroneous, the experiments fallacious, and that the
expanded air consumes more heating power than steam.
In one of the favourable notices of Mr. Ericsson's engine in an
American publication, it is thus described:--"Two caloric engines have
been constructed in New York, one of 5-horse power, the other of 60.
The latter has four cylinders; two of 6 feet diameter, placed side by
side, surmounted by two of much smaller size. Within are pistons, so
connected that those in the lower and upper cylinders move together.
A fire is placed under the bottom of the large cylinders, called the
working cylinders; those above are called the supply cylinders. As
the piston in the supply cylinder moves down, valves at the top admit
the air. As they rise, those valves close, and the air passes into
a receiver and regenerator, where it is heated to about 450°, and
entering the next working cylinder, it is further heated by a fire
underneath to 485°. The air is thus expanded to double its volume;
and supposing the supply cylinder to be half the size of the other,
the air, when expanded, will completely fill the larger cylinder. As
the area of the piston of the smaller cylinder will be only half that
of the larger, and as the air will be of the same pressure in both,
the total pressure on the piston of the large cylinder will be double
that on the small one. This surplus furnishes the working power of
the engine. After the air in the working cylinder has forced up the
piston within it, a valve opens; and as the air passes out, the piston
descends by gravity, and cold air rushes in, and fills the supply
cylinder.
"The most striking feature is the regenerator. It is composed of wire
net, placed together to a thickness of about 12 inches. The side
of the regenerator, near the working cylinder, is heated to a high
temperature. The air passes through it before entering the working
cylinder, and becomes heated to 450°. The additional heat of 30° is
communicated by the fire underneath to the large cylinder. The expanded
air forces the cylinder upwards, valves open, and it passes from the
cylinder, and again enters the regenerator. One side of the regenerator
is kept cool by the air on its entering in the opposite direction at
each stroke of the piston; consequently, as the air of the working
cylinder passes out, the wires abstract its heat so effectually, that
when it leaves the regenerator, it has been robbed of all except about
30°. In other words, as the air passes into the working cylinder, it
gradually receives from the regenerator about 450° of heat; and as it
passes out, this is returned to the wires, and it is thus used over and
over again; the only purpose of the fires beneath the cylinders being
to supply the 30° of heat which are lost by radiation and expansion.
"The regenerator in the 60-horse engine measures 26 inches in height
and width. Each disc of wire composing it contains 676 superficial
square inches, and the net has 10 meshes to the inch. Each superficial
inch, therefore, contains 100 meshes, and there are 67,600 in each
disc; and as 200 discs are employed, the regenerator contains
13,520,000 meshes, with an equal number of small spaces between the
discs as there are meshes; therefore, the air is distributed into
27,000,000 of minute cells. The wire in each disc is 1,140 feet long;
and the total length of wire in the regenerator is 41½ miles, or equal
to the surface of four steam boilers, each 40 feet long and 4 feet
diameter."
The accounts received from America of the great success that had
attended the working of Mr. Ericsson's air engine, on the ship
"Ericsson," attracted much attention in this country, and formed
the subject of two evenings' discussion in the Institution of Civil
Engineers. The most prevalent opinion was, that it is impossible to
regain the heating power without corresponding loss of mechanical force
or the addition of heat, and that there must have been some fallacy in
the reports of the work done and of the quantity of fuel consumed.
It is, indeed, evident that nothing approaching the amount of heat
said to have been recovered could be regained by passing through
the regenerator; for as the apparatus becomes heated by the first
portions of air passing through it, the temperature of the quantity
that afterwards passed must at least be equal to that of the heated
wires, and the last portions of air would consequently scarcely part
with any caloric to the regenerator, previously heated to nearly
its own temperature. Experience has since proved that the notion of
regaining the heat by the regenerator was fallacious, for in the
last improvements in Mr. Ericsson's engine, it is stated that the
regenerator has been abandoned, and the plan has been adopted of
cooling the air as it issues from the large cylinder, by passing it
through tubes surrounded by cold water, and then using the same air
over again.
One great practical inconvenience in the use of the air engine was the
necessity of having enormously large cylinders to attain the required
power, with the low amount of pressure that can be procured by the
expansion of the air. The consequent friction increased the loss of
power, and the difficulty of lubricating the pistons added to the
practical objections to the air engine. To overcome these objections,
the air in Mr. Stirling's engine is compressed before it is heated, by
which means an equal amount of pressure is obtained on a smaller piston.
The air engine would in many respects possess advantages over the steam
engine, if it could be worked economically. The space occupied by the
boilers would be saved, and the danger of explosions would be avoided;
for hot air does not scald, and the quantity at any time expanded would
be too small to do much injury.
A patent has since been obtained by Messrs. Napier and Rankine, for
improvements in the air engine, which they anticipated would remove
the objections that have been raised to the engines of Stirling and
Ericsson. The heating surface has been greatly increased by employing
tubes; and other defects in the former engines, to which their want
of complete success is attributed, have been remedied, so that Mr.
Rankine, in his description of the improvements at the meeting of the
British Association at Liverpool, confidently anticipated to effect a
great saving of heating power, combined with the other advantages of
the air engine. He estimated the consumption of fuel by a theoretically
perfect air engine on Mr. Stirling's principle at 0·37 lbs. per horse
power per hour; whilst a theoretically perfect steam engine would
consume 1·86 lbs. The actual average consumption of a steam engine
is, however, 4 lbs. of fuel per horse power per hour, and the actual
consumption of Stirling's engine is stated by Mr. Rankine to have
been 2·20 lbs, and that of Ericsson's 2·80 lbs. It appears from this
statement, therefore, that the air engines of Messrs. Stirling and
Ericsson are superior in point of economy of fuel to steam engines; and
if Mr. Rankine's anticipations of the superiority of his air engine be
realized, it will effect still greater economy. In Messrs. Napier and
Rankine's engine, the air is compressed before expansion, so that the
size of the cylinders may be reduced to even smaller dimensions than
the cylinders of steam engines of equal power.
PHOTOGRAPHY.
The power we now possess of fixing the transient impression of the rays
of light, and of retaining the beautiful images of the camera obscura,
is perhaps the most astonishing of the present age of wonders. Effects
similar to those of the electric telegraph, of steam navigation, of
dissolving views, and of other wondrous realizations of inventive
genius, had been anticipated in growing tales of Eastern romance
centuries ago; but the most fanciful imagination had not conceived the
possibility of making Nature her own artist, and of producing, in the
twinkling of an eye, a permanent representation of all the objects
comprehended within the range of vision.
Such an idea could scarcely have occurred until after the invention of
the camera obscura; but when looking at the beautiful pictures focused
on the screen of that instrument, it became an object of longing desire
to fix them there.
To trace the history of Photography from its earliest beginnings, we
must go back to the days of the alchemists, who were the discoverers
of the influence of light in darkening the salts of silver, on which
all photographic processes on paper depend. That property of light was
noticed in 1566, and it induced the speculative philosophers of that
day to conceive that luminous rays contained a sulphurous principle
which transmitted the forms of matter. Homberg, more than a century
afterwards, misled by this action of the sun's rays, supposed that they
insinuated themselves into the particles of bodies, and increased their
weight; and Sir Isaac Newton also entertained a similar opinion.
The influence of the solar rays in facilitating the crystallization of
saltpetre and sal ammoniac, was shown by Petit in 1722; and in 1777,
the distinguished chemist Scheele discovered that the violet rays of
the spectrum possess greater power in producing those changes than
any other. A solution of nitrate of silver, then called "the acid of
silver," was known to be peculiarly susceptible to the action of those
rays. The experiment by which it was illustrated consisted in pouring
the solution on chalk, which became blackened by exposure to light.
These discoveries were made by Scheele in his endeavours to find in
light the source of "phlogiston"--that _ignis fatuus_ of the chemists
of the last century. We thus perceive, in the first steps towards the
invention of Photography, one of the many instances of the discovery of
truth in the search after error.
At the beginning of the present century, Mr. Wedgwood, the celebrated
porcelain manufacturer, undertook a series of experiments to fix the
images of the camera, assisted by Mr. (afterwards Sir Humphry) Davy.
They so far succeeded as to impress the images on the screen, but
unfortunately they had not the power of preserving the paper from
being blackened all over when exposed for a short time to the light.
"Nothing," said Sir Humphry Davy, in his account of these experiments,
"but a method of preventing the unshaded parts of the delineation from
being coloured by exposure to light is wanting to render this process
as useful as it is elegant."
It was in June, 1802, that Mr. T. Wedgwood published "an account of a
method of copying paintings on glass, and of making profiles by the
agency of light; with observations by H. Davy." Mr. Wedgwood made use
of white paper or white leather, moistened with a solution of nitrate
of silver. The following description of the process, contributed to
the "Journals of the Royal Institution" by Davy, will be read with
interest, as showing how closely these experiments approximated to
the photogenic process, invented by Mr. Talbot thirty-six years
afterwards:--
"White paper or white leather moistened with a solution of nitrate
of silver undergoes no change in a dark place; but on being exposed
to daylight, it speedily changes colour, and after passing through
different shades of grey and brown, becomes at length nearly black;
the alterations of colour take place more speedily in proportion as
the light is more intense. In the direct rays of the sun, two or three
minutes are sufficient to produce the full effect. In the shade,
several hours are required; and light transmitted through different
coloured glasses acts on it with different degrees of intensity.
Thus it is found that red rays, or the common sunbeams passed through
red glass, have very little action on it. Yellow or green are more
efficacious; but blue and violet light produce the most decided and
powerful effects.
"When the shadow of any figure is thrown on the prepared surfaced, the
part concealed by it remains white, and the other parts speedily become
dark. For copying paintings on glass, the solution should be applied on
leather, and in this case it is more readily acted on than when paper
is used. When the colour has been once fixed on leather or paper, it
cannot be removed by the application of water, or water and soap, and
it is in a high degree permanent. The copy of a painting or a profile,
immediately after being taken, must be kept in a dark place. It may,
indeed, be examined in the shade, but in this case the exposure should
only be for a few minutes; by the light of candles or lamps, it is
not sensibly affected. No attempts that have been made to prevent the
uncoloured parts of the copy or profile from being acted upon by light,
have as yet been successful. They have been covered with a coating
of fine varnish, but this has not destroyed their susceptibility of
becoming coloured; and even after repeated washings, sufficient of the
active part of the saline matter will still adhere to the white parts
of the leather or paper, to cause them to become dark when exposed to
the rays of the sun.
"The woody fibres of leaves, and the wings of insects, may be pretty
accurately copied; and in this case it is only necessary to cause the
direct solar light to pass through them, and to receive the shadows
on prepared leather. Images formed by means of the camera obscura
have been found too faint to produce, in any moderate time, an effect
on nitrate of silver. To copy those images was the first object of
Mr. Wedgwood in his researches on this subject, and for this purpose
he first used the nitrate of silver, which was mentioned to him by a
friend as a substance very sensible to the influence of light; but all
his numerous experiments, as to their primary end, proved unsuccessful."
It will be seen, from the foregoing account of the results of their
experiments, that Mr. Wedgwood's process and the early processes
of Mr. Talbot were nearly alike; and if he had possessed the means
which the compound salt hyposulphite of soda afforded to subsequent
photographers, of destroying the sensibility of the prepared paper to
further impressions of the rays of light, there can be little doubt
that the invention would have attained a high degree of perfection at
the commencement of the present century. As it was, the failure of Mr.
Wedgwood to accomplish the object he was so nearly attaining appears to
have discouraged attempts by others, and twenty years elapsed without
any advance having been made towards its realization.
M. Niepce, of Chalons on the Saone, who was the first to succeed in
obtaining permanent representations of the images of the camera,
commenced experimenting on the subject in 1814, at least ten years
before M. Daguerre directed his attention to Photography. In 1826
these two gentlemen became acquainted, and conjointly prosecuted
the investigations which led to the beautiful result of the
Daguerreotype. M. Niepce having previously succeeded in obtaining
durable representations of the pictures focused in the camera, he
came to this country in 1827, and exhibited several of the results
of his process, and communicated to the Royal Society an account of
his experiments. These photographs, which may be considered the first
durable ones that had been obtained, were, with one exception, taken
on plates made of pewter. One of the largest was 5¼ inches long and 4
inches wide. It was taken from a print 2½ feet in length, representing
the ruins of an abbey. When seen in a proper light, the impression
appeared very distinct. Another one, which was stated to have been the
first successful attempt, was a view taken from nature, representing
a court-yard. Its size was 7½ inches by 6 inches, but it was not so
distinct as the preceding one. A third specimen was an impression on
paper, _printed from a photograph on metal_, the picture having been
etched into the plate by nitric acid, and then printed from. All these
specimens, though extremely curious as the first successful attempts
to preserve the images of the camera, were more or less imperfect,
and were far from presenting the beautiful results of Photography now
attained. It is remarkable, however, that the original process of
etching the picture on a metal plate, and printing from it, has now, in
the perfected state of the art, become the most recent improvement;
and the prints from photographic plates present some of the most
beautiful effects hitherto produced.[2]
M. Niepce communicated the particulars of his process to M. Daguerre
in December, 1829. They then entered into an agreement to pursue their
investigations jointly, but it was not until ten years afterwards that
the invention of the Daguerreotype by M. Daguerre was made known.
To M. Niepce must, therefore, be awarded the honour of having first
discovered the means of rendering permanent the transient images of
the camera obscura. The plan he adopted was to cover a plate of white
metal with asphalte varnish, and expose it to the action of light in
a camera, when the parts whereon the light was concentrated became
hardened, and the other parts remained unaltered, and could be washed
away.
In M. Niepce's account of the process, after describing the preparation
of the asphalte varnish, he says:--"A tablet of _plated silver_, or
well-cleaned and warm _glass_, is to be highly polished, on which a
thin coating of varnish is to be applied cold, with a light roll of
very soft skin. This will impart to it a fine vermilion colour, and
cover it with a very thin and equal coating. The plate is then placed
on heated iron, which is wrapped round with several folds of paper,
from which, by this method, all moisture has been previously expelled.
When the varnish has ceased to simmer, the plate is withdrawn from the
heat and left to cool and dry in a gentle temperature, and protected
from a damp atmosphere. The plate, thus prepared, may be immediately
subjected to the action of the luminous fluid in the focus of the
camera; but even after having been thus exposed a length of time
sufficient for receiving the impressions of external objects, nothing
is apparent to show that these impressions exist. The forms of the
future picture remain still invisible. The next operation then is to
disengage the shrouded image, and this is accomplished by a solvent."
The solvent employed was a mixture of one part of oil of lavender, and
ten parts of oil of petroleum. The solvent was poured over the plate,
and allowed to remain. M. Niepce continues: "The operator, observing
it by reflected light, begins to perceive the images of the objects
to which it has been exposed gradually unfolding their forms, though
still veiled by the supernatant fluid, continually becoming darker from
saturation with the varnish."
The time required for the exposure of the plates in the camera was six
or eight hours. For the purpose of darkening the pictures, M. Niepce
used iodine, and it has been supposed that the use of iodine for that
purpose suggested the employment of it to his partner.
The process adopted by M. Daguerre was, to deposit a film of iodine on
a highly polished silver plate, by exposing the plate to the vapour
of iodine in a dark box. The prepared plate was then placed in the
camera, and after an exposure of ten minutes or more, according to the
brightness of the day, an impression was made on the iodised silver,
but too faint to be visible. To bring out the image thus invisibly
impressed, the plate was exposed to the vapour of mercury, in a closed
box. The mercury adhered to the parts on which the light had acted,
and left the other parts of the plate untouched; and by this means a
beautiful representation was produced, in which the deposited mercury
represented the lights of the picture, and the polished silver the
shadows. The iodised silver remaining on the plate not acted on by
light, was washed away by a solution of hyposulphite of soda, and the
picture could then be exposed without injury.
Nothing can exceed the delicacy of delineation by such a Daguerreotype;
for the fine surface of the highly polished silver seems to exhibit the
impressions of the smallest objects that emit rays of light. The length
of time required to produce an impression was, however, a serious
obstacle to the use of the process, as originally invented, for taking
portraits. Numerous attempts were consequently made to obtain a more
sensitive material. Bromine was tried, in addition to iodine, and with
such complete success, that a few seconds were sufficient to effect an
impression on the plate, which could be forcibly brought out by the
vapour of mercury.
It was in 1840 that portraits were first taken by the Daguerreotype
process in this country. In the first instance, a concave mirror was
employed to concentrate the rays of light on the plate, instead of a
lens; and the author has now in his possession a portrait taken in
this manner, by "Wolcott's reflecting apparatus." The object of using
a concave mirror was to be able to concentrate a greater number of the
rays of light than could be done by a lens, and thus to form a brighter
image. At the time that portrait was taken, the means had not been
discovered of making the mercury adhere to the plate, and a feather
would brush it away. Soon afterwards, however, M. Fizeau ingeniously
contrived to fix the images on the plate by gilding it. This was done
by pouring on to the plate a few drops of a diluted solution of muriate
of gold, and holding it horizontally over the flame of a spirit lamp;
by which means the gold was deposited and formed a thin, beautiful film
of the metal over the surface, and thus not only made the picture more
durable, but gave it increased effect.
The French government, fully appreciating the importance of the
invention, determined to purchase it from the patentee, and to throw it
open to the public. An account of the invention was published in June,
1839; and in the following month an arrangement was entered into, to
the effect that, in consideration of M. Daguerre making the process
fully known, a pension of 6,000 francs should be granted to him for
life, and a pension of 4,000 francs to M. Isidore Niepce, the nephew of
the original inventor of Photography, his uncle having died before the
final success was attained.
It was generally supposed at the time, that by the grant of those
pensions the invention was thrown open to the whole world, as
represented by the French Minister; but, nevertheless, M. Daguerre
patented the process in other countries, and France alone reaped the
benefit of a free use of the invention.
Whilst M. Daguerre was thus successfully working out to perfection the
plan of producing beautiful naturally-impressed pictures on iodised
silver surfaces, Mr. Fox Talbot was at the same time nearly attaining
the same results. The following is the account given by himself of his
researches:[3]--"Having in the year 1834 discovered the principles of
Photography on paper, I some time afterwards made some experiments on
metal plates; and in 1838 I discovered a method of rendering a silver
plate sensitive to light, by exposing it to iodine vapours. I was at
that time, therefore, treading in the footsteps of M. Daguerre, without
knowing that he, or indeed any other person, was pursuing, or had
commenced or thought of, the art which we now call Photography. But
as I was not aware of the power of mercurial vapour to bring out the
latent impressions, I found my plates of iodised silver deficient in
sensibility, and therefore continued to use in preference my photogenic
drawing paper. This was in 1838. Some time after--in August, 1839--M.
Daguerre published an account of his perfected process, which reached
us during the meeting of the British Association; and I took the
opportunity to lay before the Section the facts which I had myself
ascertained in Metallic Photography."
Whilst to M. Daguerre must be awarded the honour of having first
brought to perfection the method of rendering permanent the images of
the camera on metal plates, Mr. Fox Talbot may claim to be the first
who perfected similar images on paper, which the comparative roughness
of the surface alone prevented from being as delicately beautiful
as the pictures of the Daguerreotype. He commenced his experiments
in Photography in 1834; and on the 31st of January, 1839, he read a
paper before the Royal Society, entitled, "Some Account of the Art of
Photogenic Drawing; or, a process by which natural objects may be made
to delineate themselves without the aid of the artist's pencil."
Mr. Talbot had not then succeeded in obtaining the impressions of
images focused in the camera; what he had succeeded in doing was to fix
upon paper the shadows of objects placed upon it, and exposed to the
light of the sun. The paper was first dipped into a solution of common
salt, and then wiped dry, to diffuse the salt uniformly through the
substance of the paper. A solution of nitrate of silver was then spread
over one surface with a soft brush, and dried carefully before a fire
in a darkened room. The strength of the solution was regulated by first
obtaining a saturated solution of the nitrate of silver, and afterwards
diluting it with six or eight times its volume of water. The objects to
be copied, such as leaves, lace, or other flat surfaces, were pressed
against the prepared paper by a glass fixed in a frame, and exposure
to light quickly darkened all the parts of the paper, excepting those
shaded by the objects. The image thus impressed was what is termed a
"negative," the dark parts which excluded the light being left white on
the paper, and the parts through which the light passed being darkened.
To produce a picture corresponding with the natural lights and shades,
the process was repeated, substituting the picture first obtained, on
thin transparent paper, for the original object, by which means the
lights and shadows were reversed.
The chloride of silver, formed on the surface of the sensitive paper
by the combination of the common salt and nitrate of silver, being
insoluble in water, great difficulty was experienced in washing it
away, so as to prevent the whole surface from afterwards darkening
on exposure to light. The application of hyposulphite of soda, for
the purpose of making the pictures durable, was suggested by Sir John
Herschel, and it answers remarkably well, as it dissolves the chloride
of silver. A solution of ammonia is nearly equally efficacious in
removing the chloride.
The Calotype process, by which the images of the camera can be
fixed upon paper, was invented by Mr. Talbot, in 1840. It is thus
described:--Dissolve 100 grains of crystallized nitrate of silver in 6
ounces of distilled water. Procure some fine writing paper, and wash
one side of it with the solution, laid on with a soft brush; then dry
the paper cautiously, by holding it at a distance from the fire. When
dry, dip the paper into a solution of iodide of potassium, containing
500 grains dissolved in 1 pint of water, and let it remain in the
solution two or three minutes. Then dip it into a vessel of water;
remove the water on the surface by blotting paper, and dry it by a
fire, in the dark or by candle-light. The paper thus prepared is called
"iodised paper;" it is not very sensitive to light, and may be kept for
some time without spoiling. Next dissolve 100 grains of crystallized
nitrate of silver in 2 ounces of distilled water; add to the solution
one-sixth of its volume of strong acetic acid, and call that mixture
A. Then make a strong solution of crystallized gallic acid in cold
water, and let that solution be called B. Mix equal volumes of A and
B together in small quantities at a time. That mixture Mr. Talbot
calls gallo-nitrate of silver, and with it wash over the surface of
the iodised paper. Allow the paper to remain half a minute, and then
dip it into water, and again dry it lightly with blotting paper. The
paper thus prepared is very sensitive, and will receive an impression
in the camera in the shortest possible time. The impression is at first
invisible, but it may be brought out by laying the paper aside in the
dark, or by washing it once more in the gallo-nitrate of silver, and
holding it at a short distance from the fire. To fix the picture, the
paper is first washed in water and lightly dried, and then soaked in
a solution of hyposulphite of soda for a few minutes, by which means
the iodised silver is removed, and after being again washed in water
and dried, the process is completed. The picture thus produced is a
negative one, and requires to be transferred in the manner before
stated. The original Calotype may, by that means, serve to produce a
great number of pictures.
Mr. Talbot's patent was sealed on the 8th of February, 1841. In his
specification, he claimed the use of gallic acid, and he succeeded
in enforcing his claim in a Court of Law, though it appeared that on
the 10th of April, 1839, photographs of objects taken in the solar
microscope in five minutes, by the Rev. J. B. Reade, were shown at
the London institution, which were described to have been produced by
an infusion of galls, and fixed with hyposulphite of soda. It must be
mentioned, however, to Mr. Talbot's honour, that on a representation to
him by the President of the Royal Society that the art of Photography
was impeded in its progress in this country by patent monopolies,
he generously made a present to the public of all his inventions
and discoveries, reserving to himself only the privilege of taking
portraits.
The transfer from one paper to another of the picture obtained in
the camera, and the comparative roughness of the surface of the
paper itself, prevent Calotypes from exhibiting that sharpness and
delicacy of definition which are so admirable in a Daguerreotype.
Several attempts were therefore made to obtain a more smooth surface
for the reception of the image; but without much success, until glass
was adopted for the purpose. To make that material available, it is
necessary to coat it with some substance that will absorb the sensitive
solution. In the first instance, the white of eggs was employed
with considerable success. Albumen has, however, been supplanted by
collodion--a solution of gun-cotton in ether--which is found to be
peculiarly suitable for the reception of the sensitive preparation of
silver.
In conducting the collodion process, the collodion is first iodised by
adding to it iodide of potassium and iodide of silver, dissolved in
alcohol. The iodised collodion is then poured over a plate of glass
that has been carefully cleaned, and is moved about horizontally
until a perfectly uniform film is spread over the surface, to which
it adheres firmly. The plate is afterwards dipped into a solution of
nitrate of silver, which renders it so highly sensitive to impressions
of light, that it will receive an image in less than a second. The
image is latent, until it is developed by pouring over the plate a
mixture of pyro-gallic acid in distilled water, acetic acid, and
nitrate of silver. The impression is fixed with hyposulphite of soda.
The pictures produced by the collodion process are negatives, which
serve admirably for transferring positive pictures on to sensitive
paper. But, if required, the negative picture can be readily changed
into a positive one, by converting the darkened silver into white
metallic silver, by a mixture of protosulphate of iron and pyro-gallic
acid. In a short time a white metallic image is obtained, which, when
relieved by a background of black velvet or black varnish, equals in
delicacy of finish the most beautiful Daguerreotypes.
Many attempts have been made, but hitherto without success, to obtain
photographs coloured, as well as shaded, by nature. The opinions of
those who have most studied the subject differ as to the possibility
of ever attaining that desired object. Sir John Herschel has so far
shown that it is not impossible, as to have impressed the colours of
the solar spectrum on paper, by the mere action of light; and parts
of the images of objects fixed on the screen of the camera are also
sometimes coloured. These facts induce us to hope that in the progress
of discovery some means may be found of obtaining naturally-coloured
photographs, notwithstanding it has been pronounced, by good
authorities, to be an absolute impossibility.
Specimens of coloured photographs were exhibited by Mr. Mercer at the
recent meeting of the British Association, which showed that by the
use of various chemical preparations that are sensitive to light,
photographs may be shaded in colours. The principal re-agents employed
were salts of iron, and by immersing the paper in suitable menstrua,
after the image had been impressed in the camera, the picture was
developed in any colour required; the same tint being spread over the
whole. One purpose to which it was suggested this coloured photographic
process is applicable, is printing on woven fabrics, the action of
light serving as a mordant to fix the colours.
Photography has been already applied to various uses, and it is capable
of being rendered much more valuable. To the meteorologist it affords
the means of registering the rise and fall of the mercury in the
barometer and thermometer, and, by a self-registering apparatus, the
changes of temperature and of atmospheric pressure are marked upon
paper that records the time at which the changes occur. It may also be
applied, in the same manner, to register the directions of the wind,
and the times of its changes. The sun impresses his own image upon
paper; and the spots on his surface, thus correctly delineated, can be
compared with those seen in pictures of the sun at other times; and
the foundation is laid for more correct knowledge of the nature of
those appearances, and of the motion of the sun himself. Photographs of
the moon and planets present exact representations of those heavenly
bodies, as seen through the most powerful telescope; and, with the
assistance of the stereoscope, the figure of the moon is shown in its
true globular form, as it can be seen by no other means. It has been
proposed, indeed, by the aid of Photography, to extend our knowledge
of the stars far beyond the reach of telescopic vision; for as the
image focused on the screen of the camera is composed of rays from
every object on the body of a star, it might be possible to see those
objects by greatly magnifying the image. It remains, however, for the
further progress of discovery and invention, to arrive at so delicate a
delineation by photographic processes, as to obtain landscapes of the
moon, and portraits of the inhabitants of Jupiter!
One of the latest advances in the art of Photography has been the
engraving on steel-plates by the action of light, by which means more
forcible effects have been obtained than by the impressions of light
upon paper. Mr. Fox Talbot has distinguished himself in thus fixing the
images on steel, as he was the first to impress them upon paper. In
his method of doing so, he covers the steel plate with a solution of
isinglass and bichromate of potass, and placing a collodion negative
picture upon it, he exposes it to the action of light. When the picture
is sufficiently impressed, he etches it into the plate by means of
bichloride of platinum. M. Niepce, the nephew of the original inventor
of Photography, has produced the same effect by reviving the first
processes adopted by his uncle; using, as he did, bitumen, dissolved
in essential oil of lavender, to cover the plates. Two other foreign
photographers, M. Poitevin and M. Pretschi, have also successfully
directed their attention to engraving the images of the camera, which
has now obtained a high degree of perfection.
It is well worth notice that these most recent improvements in
Photography are but further developments of the original designs of M.
Niepce, who not only succeeded in etching the pictures impressed by the
light of the sun on his metal tablets, but made use of a glass surface,
on which the now generally adopted collodion process depends.
DISSOLVING VIEWS.
There are no optical illusions more extraordinary than those shown
in the exhibition of Dissolving Views. The effects of the changes in
the diorama are only such as are seen in nature, the same scene being
represented under different circumstances, and the marvel in that case
is that such beautiful and natural effects can be produced on the
same canvas. But Dissolving Views set nature at defiance, and exhibit
metamorphoses as great as can be conceived by the wildest fancy.
Whilst, for instance, the spectator is looking at the interior of a
church, he sees the objects gradually assuming different appearances.
The columns that support the vaulted roof begin to fade away, and their
places are occupied by other forms, which gradually become better
defined and stronger, and a tree, a house, or, it may be, a rock,
thrusts the columns out of view, and the roof dims into blue sky,
chequered with clouds. The original view thus entirely disappears, and
the scene is changed from the interior of a church to open country, or
to a rocky valley. This is done, not by changing at once one scene
into another, but by substituting different individual objects, which
at first appear like faint shadows, and then, becoming more and more
vivid, at length altogether supplant their predecessors on the field of
view, and will, in their turn, be extinguished by others.
It sometimes happens that some strongly marked object resists
apparently the efforts made to dispossess it, and in the midst of a
mountainous scene will be observed the form of a chandelier or of a
statue, that occupied a distinguished place in the church that has
just vanished. In a short time, however, these relics disappear, and
the mountain, the valley, and the lake are freed from the incongruous
images of the former scene.
[Illustration]
[Illustration]
These effects are produced in a manner as simple as they are
extraordinary. All that is requisite is to have two magic lanterns
fitted on to a stand, with their tubes inclined towards each other, so
that both discs of light may exactly coincide, and form on the screen
a single disc. If paintings on glass, representing different views, be
then placed in each lantern, with the lenses adjusted to bring the rays
to a focus on the screen, the two images will be so mingled together
as to present only a confused mixture of colours. Suppose one of the
views to be the interior of a church, and the other to be a mountain
scene;--the pillars of the church will be mingled with trees and rocks,
and in the midst of the confusion there may perhaps be discerned
a strongly painted chandelier or an altar piece. When an opaque
shade is placed before the lens of either of the lanterns, to prevent
the light from reaching the screen, the previous confusion becomes
instantly clear and distinct, and the church or the landscape is seen
without any interfering images. If the opaque screen be gradually
withdrawn from one lens, and at the same time drawn in an equal degree
over the other, the different objects will again be mingled, and those
in the one scene will predominate over those in the other in proportion
to the relative quantities of light permitted to issue from each
lantern to the screen. The two first of the accompanying drawings are
thus blended together in the third, when the screen is half withdrawn
from each.
[Illustration]
It is usual to fix the opaque shade, which alternately covers and
exposes the two magic lanterns, on to a central pin, so that it may be
moved vertically up or down. The shade is so arranged, that in raising
the end to cover the lens of one lantern, the farther end descends,
and exposes, in an equal degree, the other lens. During the time that
either of the views is altogether concealed, the painting is changed;
and in this manner an unlimited number of metamorphoses may be effected.
It requires no expensive apparatus to show the effect of Dissolving
Views on a small scale. Two common magic lanterns are quite sufficient
for the purpose of private exhibition, and the angle at which they
should be fixed on their stand may be readily ascertained after a few
trials. To make the transformation more extraordinary, a man's face may
be painted on one glass and a landscape on the other; and, when the
change is made from the face to the landscape, a strongly painted eye
or nose may be seen occupying the centre of the view, long after the
other features have disappeared, until all the rays of light from that
painting have been excluded. The change from youth to age, from beauty
to ugliness, may also be shown with striking effect.
It will be observed that the principle, on which the metamorphoses
of Dissolving Views depend, is similar to that which produces the
variations in the diorama. In both cases there are two paintings on
the same space, either of which may be shown at pleasure by different
dispositions of the light; the chief difference between them being
that the Dissolving Views are seen altogether by reflected light,
whilst in the diorama the paintings at the back and front are shown
alternately by reflected and by transmitted light.
THE KALEIDOSCOPE.
No invention, on being first brought out, created so general a
sensation as the Kaleidoscope. Every person, who could buy or make one,
had a Kaleidoscope. Men, women, and children--rich and poor; in houses
or walking in the streets; in carriages, or on coaches--were to be seen
looking into the wonder-working tube, admiring the beautiful patterns
it produced, and the magical changes which the least movement of the
glass occasioned.
It was in the year 1814 that Sir David Brewster discovered the
principle on which the effects of the Kaleidoscope depend, whilst
he was engaged in experiments on the polarization of light by
successive reflections between plates of glass. The reflectors were
in some cases inclined to each other, and he remarked the circular
arrangement of the images of a candle round a centre. In afterwards
repeating the experiments of M. Biot on the action of fluids on
light, he placed the fluids in a trough formed by two plates of glass
cemented together at an angle. The eye being placed at one end, some
of the cement which pressed through between the plates appeared to be
arranged in a circular figure. The symmetry of this figure being very
remarkable, Sir David Brewster undertook to investigate the cause of
the phenomenon, and the result of his investigations was the invention
of the instrument to which he gave the name of Kaleidoscope, from the
Greek words καλος {kalos}, beautiful, ειδος {eidos}, a form, and σκοπεω
{skopeô}, to see.[4]
The Kaleidoscope in its simplest form consists of two equal strips of
plate glass, about 8 inches long and 2 inches wide, silvered on one
side, to act as reflectors. These glasses are placed one over the other
exactly, and then the edges on one side being separated, whilst the
two other edges are kept close together, they are fixed by means of
separating pieces of wood and string at the angle required. The glasses
are then fitted into a metal tube, which has an eye-hole at one end,
and at the other end of the tube there is fixed a small cell of ground
glass, to contain pieces of differently stained glass or other objects,
that are to be multiplied by reflections into beautiful symmetrical
figures. In the better kind of Kaleidoscopes, the cell containing the
objects may be turned round, by which means the pieces of glass shift
their positions, and the figures instantly change. The same effect is
produced, though in a less agreeable manner, in the common kind of
instruments, by turning the tube.
To form by the combined reflections from the two glasses a perfectly
symmetrical figure, the sector comprised between the inclined sides of
the glasses may consist of any even aliquot part of a circle. In the
accompanying diagram, the ends of the flat silvered glasses _a c_, _b
c_, are inclined at an angle of 60 degrees; therefore the circle is
completed by the junction of six sectors. In such a Kaleidoscope, the
circular figure will be formed by three reflections from each glass.
[Illustration]
[Illustration]
To make the formation of the circular figure by repeated reflections
more intelligible, we will consider it as composed of the smallest
possible number of equal divisions, as in the second diagram, in which
the circle is divided into quadrants. In such an arrangement of the
reflectors, the figure seen on looking through the central aperture
will consist of four parts. In the first place, the objects included in
the space _a b c_, between the inclined glasses, will be seen directly
by rays of light from the objects themselves; viz., the small cross
_d_, and the triangle _e_. The same field of view will be reflected
from both mirrors, by which reflection the cross on one side will
seem to be doubled, and the triangle on the other will have another
similar one added to it, to make a complete rhomb. The cross will also
be reflected by the mirror on the right side, and the triangle by the
one on the left. The images of the objects contained within the space
_a b c_, being thus presented by reflection on both sides, they become
the objects for further reflections from parts of the mirrors still
nearer the spectator. Thus the images _d_¹ on both sides are reflected
to form the single image _d_², and the images _e_¹ are in the same
manner reflected to form the second image _e_².
When the angle formed by the inclination of the mirrors divides the
circle into a greater number of sectors, the reflections of the images
are repeated, from points nearer and nearer to the eye, and the circle
is thus completed, however numerous the sectors may be; but at each
repetition of the reflection, the images will become more dim, since,
owing to the imperfection of reflecting surfaces, a portion of the
light is absorbed at each reflection.
In the first instruments that were constructed, the objects were
fixed in the field of view, therefore scarcely any change of pattern
was obtainable. It was not until some time afterwards that the idea
occurred to Sir David Brewster of producing endless changes of the
figures, by making the objects movable in a cell of glass at the end
of the instrument. He afterwards introduced other improvements in the
Kaleidoscope, for extending its range of objects, for varying the
angles of inclination, and for projecting the figures on a screen. In
the instrument, as ordinarily made, the objects to be seen properly
must be placed close to the end of the reflectors; but by the addition
to the instrument of a tube containing a lens, the rays from distant
objects are brought to a focus near the mirrors, and the image formed
there is repeated by the reflectors in the same manner as a solid
object.
The projection of the figures on a screen, by an apparatus similar to
a magic lantern, gives great additional pleasure to the effects of
the Kaleidoscope, as the figures are not only seen by several persons
at the same time, but they are presented in a magnified form. The
projection of the figures also increases the use of the instrument in
designing patterns, for which purpose it has been employed with great
advantage.
A patent for the Kaleidoscope was taken out in 1817, but the high
prices charged by the opticians who were authorized by the inventor
to sell the instrument, and the facility with which it could be
made, occasioned a general violation of the patent right, and it was
not long before the claim of Sir David Brewster, as the original
inventor, was disputed. In the indignant vindication of his claim, he
observes:--"There never was a popular invention which the labours of
envious individuals did not attempt to trace to some remote period;"
and the Kaleidoscope was not an exception. It was found that Kircher
had described the effects of repeated reflections as far back as
1630; and that Mr. Bradley had, in 1717, made a philosophical toy,
consisting of two small mirrors, that opened like a book, which, when
partially opened, repeated the reflections of objects placed near it
in the same manner as the Kaleidoscope. But this instrument was so
different in its construction, and in the effects it produced, from the
Kaleidoscope, that Sir David Brewster's claim to be the inventor may
be freely admitted. The fact that it took the world by surprise, and
created a sensation greater than any other invention had done before,
is sufficient to establish its title as an original invention.
THE MAGIC DISC.
There are several ways of illustrating the retention by the retina of
the eye of the images of objects after they have been withdrawn from
sight, but none is so curious as the philosophical toy called the Magic
Disc, which, from the optical principles involved in its extraordinary
effects, deserves to be noticed as one of the remarkable inventions of
the present century.
One of the most striking methods of exhibiting the retentive property
of the retina, before the invention of the Magic Disc, was to paint
different objects at the back and on the front of a card, and by then
giving rapid rotation to the card, both objects were seen together.
Thus, when the figure of a bird is painted on one side, and an empty
cage on the other, by rapidly turning the card, the bird appears to be
in the cage. In the Magic Disc the objects are painted on the same side
of a circular piece of card-board, and both are exposed to view during
their rapid rotation.
The disc is divided into eight or ten compartments, in each one of
which the same figures are repeated, though the positions of one
or more of them are changed. A favourite subject represented is a
clown leaping over the back of a pantaloon, which affords a simple
illustration of the apparent relative movements of two bodies, and will
serve to explain how the effect is produced.
[Illustration]
The instrument consists of a disc of stiff card-board, about nine
inches diameter, mounted on a horizontal pivot in the centre, on which
it may be freely turned. Between each of the compartments of the disc
there is an elongated aperture, about one inch long and a quarter of an
inch wide, for the eye to look through. Suppose the disc to be divided
into eight compartments, by radial lines. In the compartment No. 1,
the pantaloon is represented in a stooping posture, and the clown is
on the ground ready to make a spring. In No. 2 the pantaloon is in the
same attitude, but the clown has commenced his leap, and is raised a
little way from the ground. In the third division he is shown still
higher in the air; and in the fourth he is mounted above the shoulders
of pantaloon, who retains the same posture as at first. The fifth
compartment represents the clown as having jumped over pantaloon's
head, and coming down to the ground; and in each succeeding division
his farther descent is shown, till, in No. 8, he has reached the ground
again, and is ready to recommence the leap.
When the disc is turned rapidly round on its pivot, the figures
painted upon it are mingled together, and present a confused medley of
lines and colours, in which no object can be distinctly defined. This
mingling of the objects is caused by the retention of the images by the
retina, so that if the eye be directed to any point, the impression of
the lines and colours that pass rapidly before it is not effaced before
another and another appear to produce fresh impressions, and they
mingle together in confusion. If, for instance, there were a circle
formed of dots marked on the disc, the impression of each dot on the
retina would be prolonged; and as, by the rotation, other dots would
come into the field of view before the impression of the first was
removed, it would form an unbroken ring. But if the disc were screened
from sight, at intervals of nearly equal duration to that of the
continuous impression, so as to efface the image of one dot before the
rays of another were admitted to the eye, then the ring would be seen
to be composed of dots, as distinctly as when the disc was stationary.
The effect of screening the objects from the eye at short intervals
is produced by looking with one eye through the openings at the image
of the disc, reflected from a mirror. The figures are then seen only
when the apertures come opposite the eye; but as the impression of one
view remains till it is renewed by the light admitted through the next
aperture, there is continuous vision of the objects painted on the disc.
It is thus that the figures of pantaloon and clown become visible, and
their apparent relative movements are occasioned. For instance; each
time that the impression of the figure of the pantaloon is renewed,
he is seen in the same place and in the same attitude; therefore he
appears to be stationary, though the successive pictures that compose
his figure to the eye are in rapid rotary motion. The figure of the
clown, however, is seen in a different position each time that he
comes into view, therefore he appears to be in motion relatively to
pantaloon, though stationary as regards his absolute position on the
disc.
The same effect would be produced if the disc, during its rotation,
were seen by successive electric sparks. The electric spark is so
momentary in its duration, that the most rapidly moving objects appear
stationary; therefore each spark would show a seemingly stationary
disc, on which the figure of the clown would appear in different
relative positions; and the illusion would be as perfect as when the
rays of light are interrupted at intervals.
The electric spark is so instantaneous that a cannon ball might be
seen in its rapid flight, if illuminated by a flash of lightning, and
would seem to be stationary. Professor Faraday mentioned, in one of his
lectures, the extraordinary appearance which a man, who was jumping
over a stile, presented when seen by lightning on a dark night. The man
seemed to be resting horizontally in the air, with one hand touching
the stile.
The duration of the impression of an object on the retina is capable of
illustration by means of the Magic Disc in a great variety of designs,
each one of which may represent many movements. The turning of the
wheels of machinery, the tossing of balls, the dancing figures of men
and women may thus be shown, the designs for which afford ample scope
for exercising the pencil of an ingenious artist.
THE DIORAMA.
Those who are old enough to remember the Regent's Park before there
were any houses northward of the New Road, may recollect that among
the first buildings erected, on what is now called Park Square, was a
strange-looking, partly semi-circular erection, provided with ample
lighting space, which attracted great attention during its progress,
and was the cause of much speculation as to its probable purpose. That
building was intended for the exhibition of the Diorama.
M. Daguerre, the inventor of the Daguerreotype, had, in conjunction
with M. Bouton, a short time previously opened a similar exhibition in
Paris, where the beauty of the paintings, aided by the extraordinary
effects of newly contrived dispositions of the light, had excited
a great sensation. The Diorama was opened in London on the 6th of
October, 1823, and for a long time it was equally popular in this
metropolis.
The visitors, after passing through a gloomy anteroom, were ushered
into a circular chamber, apparently quite dark. One or two small
shrouded lamps placed on the floor served dimly to light the way
to a few descending steps, and the voice of an invisible guide gave
directions to walk forward. The eye soon became sufficiently accustomed
to the darkness to distinguish the objects around, and to perceive
that there were several persons seated on benches opposite an open
space, resembling a large window. Through the window was seen the
interior of a cathedral, undergoing partial repair, with the figures
of two or three workmen resting from their labour. The pillars, the
arches, the stone floor and steps, stained with damp, and the planks
of wood strewn on the ground, all seemed to stand out in bold relief,
so solidly as not to admit a doubt of their substantiality, whilst the
floor extended to the distant pillars, temptingly inviting the tread
of exploring footsteps. Few could be persuaded that what they saw was
a mere painting on a flat surface. This impression was strengthened
by perceiving the light and shadows change, as if clouds were passing
over the sun, the rays of which occasionally shone through the
painted windows, casting coloured shadows on the floor. Then shortly
the brightness would disappear, and the former gloom again obscure
the objects that had been momentarily illuminated. The illusion was
rendered more perfect by the excellence of the painting, and by the
sensitive condition of the eye in the darkness of the surrounding
chamber. Whilst gazing in wrapt admiration at the architectural
beauties of the cathedral, the spectator's attention was disturbed by
sounds underground. He became conscious that the scene before him was
slowly moving away, and he obtained a glimpse of another and very
different prospect, which gradually advanced until it was completely
developed, and the cathedral had disappeared. What he now saw was a
valley, surrounded by high mountains capped with snow. This mountain
valley seemed scarcely less real than the arched roof and columns of
the cathedral, whilst a foaming cascade, dashing down the rocks, and
the sound of rushing waters, added to the illusion. After looking for
some time at this beautiful valley, the clouds were seen to gather on
the mountain tops, and a storm impended. A gleam of sun-light, still
resting on the edge of the clouds, exhibited a strange contrast between
the silvery brightness and the dense black vapour that shrouded the
hills, and could almost be felt. It was but a passing thunderstorm.
Presently the dark clouds rose from the valley, and dispersed; the sun
again shone on cottage, vineyard, and mountain, charming the spectator
as much by the beauty of the scene as he was astonished by the
wonderful change.
Such was the Diorama as it was first exhibited in London to admiring
crowds. In subsequent years greater changes were made in the variations
of light and shade; and by the introduction of mechanical contrivances,
with more or less success, the magical effects were increased, without,
however, adding to the apparent reality of the objects. A church or
cathedral was always the subject of one view, and sometimes of both.
The interior of an empty church would be shown by evening twilight.
The shades of evening gradually darkened into the obscurity of
night, and then the glimmer of candles would be seen spreading more
and more widely, until the church was lighted up, and it was occupied
by a crowded congregation at midnight mass. Some views represented
the exterior of a ruin or of a cathedral after sunset, and as night
advanced, the stars twinkled in the blue sky, and the moon rose and
threw its silvery light on water, buildings, and clouds, contrasting
in some cases with the red glare of lamps from the windows of houses
and shops. The disc of the moon exactly resembled that of the real
luminary, and all around being so dark, the rays from its surface cast
shadows of intervening objects. In one picture a still more astonishing
appearance was produced, by the change of the interior of a beautifully
painted and decorated church into a mass of charred ruins.
The means principally adopted for the production of these magical
changes in a painting on a flat surface, and for giving such seeming
reality to the objects represented, were for some time kept secret;
nor do we think they are even yet much known. As in many other clever
inventions, the effects are produced in a very simple manner. The
picture is painted on both sides of a transparent screen, and the
change of scene is occasioned almost entirely by exhibiting the picture
at one time by reflected light, from the surface nearest the spectator,
and afterwards by transmitted light, after excluding the light from the
front.
Let us take for illustration the interior of a church, at first seen
empty, and afterwards filled with people, and illuminated by candles.
The empty church is painted on the front on fine canvas or silk, in
transparent colours, and at the back are the figures and candles,
and other objects intended to appear with them. The arrangements for
illuminating the picture are so contrived, that the light may be thrown
entirely on the front or on the back, or partly on both. When the light
is on the front, the empty church only is visible. It is then gradually
darkened, and the back of the picture is illuminated, by which means
the figures and candles are seen; and the form of the building being
preserved, the same church, which was before empty, becomes occupied by
a crowded congregation.
It may be mentioned, as an illustration of the perfect illusion of
the Diorama, that a lady who on one occasion accompanied the author
to the exhibition, was so fully convinced that the church represented
was real, that she asked to be conducted down the steps to walk in the
building.
[Illustration]
The effect of changing the direction of the light may be readily
perceived by making a drawing on both sides of a sheet of paper, as
shown in the annexed engraving. The side backing this page represents
the interior of St. Paul's Cathedral when empty, and on the back
several figures are drawn. Those figures are invisible until the
leaf is held up against the light, and when the drawing is seen as a
transparency, the objects on the back, as well as those in front, come
into view, and the building appears to be occupied.
[Illustration]
Any one who has a taste for drawing, and a little ingenuity, may thus
produce many pleasing and astonishing effects. It will be desirable
to procure, in the first instance, a box, so contrived that it will
hold the painting, and afford the means of throwing the light on the
front or on the back at pleasure. The diagram shows the form of such
a box. The letters _a_, _b_, _c_, _d_ mark the outside; the aperture,
at _c d_, being enlarged to permit several persons to look into it at
the same time. The box may be of any required dimensions, to suit the
size of the drawing, which is to be fitted into a groove at _a b_,
and the interior must be blackened. The lid, _e_, when open, as in
the diagram, admits the light to the front of the picture, the back
being covered with an opaque screen. As the lid is closed, the picture
becomes darkened, and by the gradual removal of the screen at the same
time, it is changed into a transparency. This portable Diorama can be
most conveniently shown by lamplight, the flame of an argand lamp, the
wick of which can be heightened and lowered, being best adapted for
the purpose. The effect by daylight is, however, superior, but the
room must then be darkened, and the admission of light confined to the
picture.
[Illustration]
The moving water, and the motion of smoke and clouds, which were
frequently introduced in the Diorama, were mechanical additions, the
effects being produced by giving motion to bodies behind, the forms
of which were seen by transmitted light. The introduction of such
mechanical aids, however, detract from the artistic character of the
Diorama, the principal merit of which consists in exhibiting the
changes occasioned by variations in the mode of throwing the light on
the two-faced picture.
It is to be regretted that exhibitions of a larger and more showy kind
should have superseded the Diorama in public estimation; and that,
from the want of support, their charming and marvellous pictorial
representations, which formed, in days gone by, one of the principal
"sights" of London, should be now closed.
THE STEREOSCOPE.
One of the most beautiful as well as the most remarkable pictorial
illusions is produced by the combination of two views into one by the
recently invented instrument called the Stereoscope. In the Diorama, in
the Magic Disc, and in the Dissolving Views, separate paintings combine
to produce different effects; but in the Stereoscope the two pictures
unite into one to give additional effect to the same view, and to make
that which is a flat surface, when seen singly, appear to project like
a solid body.
The principle of the Stereoscope depends on the different appearance
which near objects present when seen by the right or by the left eye.
For instance, on looking at a book placed edgewise, with the right eye,
the back and one side of the book will be perceived; and on closing
the right eye and opening the left, the back and the other side of the
book will be seen, and the right-hand side will be invisible. It is the
combination of both these views by vision with two eyes that produces
the impression of solidity of objects on the mind; and if the different
appearances which the book presents to each eye be copied in separate
drawings, and they can afterwards be placed in such a position as to
form a united image on the retinæ of the eyes, the same effect is
produced as if the book itself were looked upon.
[Illustration]
This diagram represents the outlines of a near object, as seen by each
eye separately. The one on the right hand shows it as seen with the
right eye, and the other as it looks with the left eye; and if both
drawings be combined into one image, it stands out in bold relief.
This may be done without any instrument, by squinting at them; but
the effect is more readily and far more agreeably produced by the
Stereoscope, so named from the Greek words στερος {steros}, solid, and
σκοπεω {skopeô}, to see.
Professor Wheatstone claims to be the first who contrived an instrument
to illustrate this effect of binocular vision, and he also claims to be
the first who brought to notice the different appearances of objects
seen with each eye separately. Sir David Brewster, however, disputes,
on behalf of Mr. Elliot, of Edinburgh, Professor Wheatstone's claim to
the invention of the first stereoscopic instrument; and he has shown
that the difference of vision with each eye was remarked by Galen,
1,700 years ago; that it was noticed by Leonardo da Vinci in 1500, and
formed the subject of a treatise by a Jesuit, named Francis Aquilonius,
in 1613; and that it was a well-known phenomenon of vision long before
it was mentioned by Professor Wheatstone.[5] Mr. Elliot, though he
conceived the idea, in 1834, of constructing an instrument for uniting
two dissimilar pictures, did not carry it into effect until 1839, the
year after Mr. Wheatstone had exhibited his reflecting Stereoscope to
the Royal Society, and at the meeting of the British Association.
Mr. Elliot's contrivance, to which Sir David Brewster is inclined to
give precedence in point of date, was very inferior in its effects
to the reflecting Stereoscope. It was without lenses or mirrors, and
consisted of a wooden box 18 inches long, 7 inches broad, and 4½ deep,
and at the end of it was placed the dissimilar pictures, as seen by
each eye, that were to be united into one. The view he drew for the
purpose comprised the moon, a cross, and the stump of a tree, at
different distances; and when looked at in the box, the cross and the
stump of the tree appeared to stand out in relief.
The accompanying woodcut represents the original stereoscopic pictures,
copied from Sir David Brewster's book; and by looking towards the
picture on the left with the right eye, and on the right-hand picture
with the left eye, the two will be seen united, and the cross and the
stump of the tree will appear to stand out solidly.
[Illustration]
The arrangement of the apparatus, as described by Professor Wheatstone,
in his paper read before the Royal Society, consists of two plane
mirrors, about 4 inches square, placed at right angles; and the
drawings, made on separate pieces of paper, were reflected to the eyes
looking into the mirrors at their junction. The diagram is a sketch of
this arrangement. In the middle of a narrow slip of wood, _d e_, about
12 inches long, the two mirrors, _a b_, are fixed, inclined at the
required angle from their line of junction at _c_. Upright pieces of
wood, _d h_, _e f_, at each end, are furnished with slides or clips to
hold the drawings, which are reflected from the inclined mirrors, and
seen in them by each eye separately. Thus, the left eye sees only the
picture fixed on _d h_, and the right eye sees the one placed at _e f_;
and the two images, being combined at the seat of vision, produce the
same impression as a solid body.
[Illustration]
It is almost unnecessary to describe the external appearance of the
lenticular instrument invented by Sir David Brewster, and explained by
him at the meeting of the British Association in 1849. In the best kind
of instruments the glasses, through which the pictures are seen, are
composed of a single large double-convex lens, divided in the middle,
the thin edges being set towards each other, about 2½ inches apart. The
more improved instruments, indeed, are made from lenses upwards of 3
inches in diameter, which, being cut into two, and the thin parts being
ground flat, are set edge to edge, and from an aperture sufficiently
large for both eyes to look through. By this means the instrument
suits all eyes, without requiring adjustment, and the field of view is
increased. A diaphragm, or partition, placed at the junction of the two
lenses, confines the vision of each eye to its appropriated picture,
and thus tends to prevent the confusion of images that might otherwise
arise.
The object of using semi-lenses is to facilitate the union of the two
pictures into one, by looking through the lens towards its edge,
instead of through the centre, the image being thus refracted to a
different position. This may be easily exemplified by looking at an
object steadily through different parts of the same lens. After looking
at it with the right eye through the centre, and whilst keeping the
axis of the eye in the same direction, move the lens slowly towards the
right, so as to bring the edge of the lens opposite the pupil. This
movement of the lens towards the right hand will be accompanied by an
apparent movement of the image towards the left, so as to bring it to a
point between the two eyes. If the experiment be repeated with the left
eye, the image will be removed towards the right hand; and thus, by
looking at the two stereoscopic pictures through the thin parts of two
lenses, the images are superposed and form a single one.
Sir David Brewster attached much importance to the semi-lenses, which
have the effect of prisms in refracting the rays of light; but that
form of lens is not essential to give apparent solidity to the images;
and many of the commoner kind of instruments are now made with ordinary
double-convex lenses, and without any partition. With the semi-lens,
however, there is less difficulty in uniting the two pictures into one
than when an ordinary lens is employed.
In taking photographic pictures for the Stereoscope with a single
camera, it is necessary to alter the angle of the instrument after
having taken one picture, to direct it to the same object in the
angle of vision as seen by the other eye. This method of producing
stereoscopic pictures with the same camera is very objectionable when
any moving objects are in the field; for they will be in a different
position in each, and sometimes disappear altogether from the second
picture. The plan adopted by the best photographers is to have two
cameras set at the requisite angle to each other, so that both pictures
or portraits may be taken at the same time.
At the meeting of the British Association in 1853, M. Claudet
endeavoured to establish some rules for the angle at which photographic
pictures must be taken, in order to produce the best effect of relief
and distance without exaggeration. He observed, that in looking at a
single picture with two eyes, there is less relief and less distance
than when looking at it with one eye, because in the latter case we
have the same effect we are accustomed to feel when we look at the
natural objects with one eye; while, if we look at the single picture
with two eyes, we have on the two retinæ the same image with the same
perspective, which is not natural, and the eyes have not to make the
usual effort for altering their convergence according to the plane on
which the object observed is situated. This inaction of the convergence
of the eyes diminishes the illusion of the picture, because the same
convergence for all the objects represented gives an idea that they
are all placed on the same plane. The photographic image being the
representation of two different perspectives, we must, when we look
at them in the Stereoscope, as when looking at the natural objects
themselves, converge, more or less, the axes of the eyes. Therefore
we make the same effort, and have the same sensation in regarding
the combined photographic pictures, as when we look at the objects
represented.
Sir David Brewster has suggested various applications of the
Stereoscope; viz., to painting, to sculpture and engineering, to
natural history, to education, and to purposes of amusement. The latter
is the principal purpose to which the instrument is at present applied;
and some of the many ways in which it may contribute to delight the
spectator are pointed out in Sir David Brewster's book.
"For the purpose of amusement," he observes, "the photographer might
carry us even into the regions of the supernatural. His art enables
him to give a spiritual appearance to one or more of his figures,
and to exhibit them as 'thin air,' amid the solid realities of the
stereoscopic picture. While a party are engaged with their whist or
their gossip, a female figure appears in the midst of them with all the
attributes of the supernatural. Her form is transparent; every object
or person beyond her being seen in shadowy but distinct outline. She
may occupy more than one place in the scene, and different portions
of the group might be made to gaze upon one or other of the visions
before them. In order to produce such a scene, the parties which are
to compose the group must have their portraits nearly finished in the
binocular camera, in the attitude which they may be supposed to assume
if the vision were real. When the party have nearly sat the proper
length of time, the female figure, suitably attired, walks quickly to
the place assigned to her, and after standing a few seconds in the
proper attitude, retires quickly, or takes as quickly a second, or even
a third, place in the picture, if it is required, in each of which she
remains a few seconds, so that her picture in these different positions
may be taken with sufficient distinctness in the negative photograph.
If these operations have been well performed, all the objects
immediately behind the female figure, having been previous to her
introduction impressed upon the negative surface, will be seen through
her, and she will have the appearance of an aërial personage, unlike
the other figures in the picture."
It is in the foregoing manner that the remarkable stereoscopic effect
of "Sir David Brewster's ghost" is produced, a representation of which
is given in the next page.
Sir David Brewster mentions many other curious applications of the
Stereoscope, among which are the dioramic effects of pictures seen
alternately by reflected and by transmitted light; a daylight view
being apparently lighted up artificially in the night, by seeing it at
one time with the light reflected from the surface, and then excluding
the light from the front, and viewing it as a transparency.
One of the most interesting effects of the Stereoscope has been
recently produced by Mr. De la Rue, who has contrived the means of
giving apparent rotundity to the surface of the moon, as viewed
through a powerful telescope. The disc of the full moon, however
highly magnified, presents, as is well-known, the appearance of a flat
surface, with the lights and shadows marked seemingly on a plane.
Owing to the great distance of that luminary, there is no variation
in its appearance, whether it be looked at with one eye or with the
other, therefore it seems removed beyond the operation of the ordinary
cause of stereoscopic effects. Nevertheless, Mr. De la Rue has taken
photographs of the moon which, when placed in the Stereoscope, combine
to form a solid-looking globe, on which all the lights and shadows are
distinctly and beautifully delineated. He has produced this effect by
taking his photographs at different periods of the year, when there is
a slight variation in the direction of the moon's face to the earth;
and by combining these separate photographs into one image in the
Stereoscope, the form of the moon appears as convex as the surface of
an artificial globe.
[Illustration]
M. Claudet, who is one of the most successful photographers in
the metropolis, has contrived an arrangement which he calls a
"Stereomonoscope," by which the appearance of solidity is communicated
to a single image formed on a screen of ground glass. The screen of
ground glass has a black back, and is placed in the focus of a lens in
an ordinary camera obscura, wherein the image may be seen by looking
down upon it. The particles of the roughened glass reflect to each
eye different parts of the image focused on the screen, and by this
means a similar effect is produced as when two dissimilar pictures are
looked at through a stereoscope instrument. One great advantage of this
arrangement is that several persons may look at the image at the same
time.
Mr. John Sang, of Kirkaldy, has very recently imparted stereoscopic
effect to copies of paintings and engravings, the flat surfaces of
which were previously thought to defy any such application of the
Stereoscope. The means he employs of doing so are at present kept
secret, but he has shown its practicability by copying, on wood
engravings, Mr. George Cruikshank's series of "The Bottle." In some
respects this process seems almost more wonderful than the original
Stereoscope, for it gives solid form and apparent substantiality to the
mere creations of the artist's pencil.
THE ELECTRIC TELEGRAPH.
No application of science has so completely realized the visions of
fancy as the Electric Telegraph. So closely, indeed, does the real of
the present day approach to the ideal of ages past, that it might be
supposed the narratives in the tales of faëry land were true records
of the inventions of former times, and that the combined efforts of
inventive genius during the last half century were but imitations and
reproductions of what had been successfully accomplished "once upon a
time." There is also an intermediate period--between the indefinite
of faëry tales and the positive of scientific history--in which
sympathetic tablets and magical loadstones, scarcely less mythical, are
stated to have been invented; and the individuals are named who thus
paved the way for instantaneous communication between all parts of the
world.
The Jesuits of the sixteenth and seventeenth centuries took the
place of the magicians of the Middle Ages. In the seclusion of their
monasteries, they speculated on the mysterious powers of Nature, then
partially revealed to them, and shadowed forth images of their possible
applications. It is to a vague speculation of this kind that we may
attribute the notice given by Strada, in his "Prolusiones Academicæ,"
of the sympathetic magnetic needles, by which two friends at a distance
were able to communicate; though the then fanciful idea has been
literally realized. A still more extraordinary foreshadowing of one
of the most recent improvements of the Electric Telegraph was the
transference of written letters from one place to another by electric
agency. This is said to have been accomplished by Kircher, who, in his
"Prolusiones Magneticæ," describes, though very vaguely, the mode of
operation. But even admitting that there were substantial foundations
for these imaginary phantasms, that would not in the least detract from
the merit of those who, following closely the footsteps of scientific
discovery, have successfully applied the principles unfolded by the
investigations of others, and by their own assiduous researches. Thus,
whilst steam navigation was facilitating the means of intercourse over
rivers and seas, and whilst railways and locomotive engines served to
bring distant cities within a few hours' journey of each other, another
source of power, infinitely more rapid in its action than steam, has
been made to transmit intelligence from place to place, and from one
country to another, with the speed of lightning.
The plan of making communications by signals has been in operation from
time immemorial; the beacon lights on hills having served in ancient
as well as in modern times to give warning of danger, or to announce
tidings of joy. Such simple signals were not capable of much variety of
expression; but even beacon lights might be made to indicate different
kinds of intelligence, by multiplying the number of the fires, and
by altering their relative positions. It was not, however, till the
invention of telegraphs that anything approaching to the means of
holding regular communication by signals was attained. The semaphore
of the brothers Chappe, of France, invented by them in 1794, was the
most perfect instrument of the kind, and was generally employed for
telegraphic purposes, until it was supplanted by the Electric Telegraph.
The semaphore consisted of an upright post, having arms on each side,
that could be readily extended, at any given angle. The extension of
these arms on one side or the other, either separately or together,
and at different angles, constituted a variety of signals sufficient
for the purposes of communication. The semaphores, erected on elevated
points, so as to be visible through telescopes, signalled intelligence
slowly from one station to another, till it reached its ultimate
destination; and thus--daylight and clear weather permitting--brief
orders could be sent from the Admiralty to Portsmouth in the course of
a few minutes. But the communication was liable to be interrupted by
fogs, as well as by nightfall.
A remarkable instance of the imperfection of sight telegraphs occurred
during the Peninsular War. A telegraphic despatch, received at the
Admiralty from Portsmouth, announced--"Lord Wellington defeated;"--and
then the communication was interrupted by a fog. This telegraphic
message caused great consternation, and the utmost anxiety was
experienced to learn the extent of the supposed disaster. When,
however, the fog dispersed, the remainder of the message gave a
completely opposite character to the news, which in its completed form
ran thus: "Lord Wellington defeated the French," &c.
Some better means of transmitting important intelligence was evidently
wanted; for not only was the semaphore liable to frequent interruptions
by the weather, but its action was very slow, and the frequent
repetitions from station to station increased the risk of blunders.
The instantaneous transmission of an electric shock suggested the
means of communicating with greatly increased rapidity; and when
it was ascertained, by experiments made by Dr. Watson at Shooter's
Hill, in 1747, that the charge of a Leyden jar could be sent through
a circuit of four miles, with velocity too great to be appreciable,
the practicability of applying electricity for conveying intelligence
became at once apparent.
Of the many means by which this object was attempted to be
accomplished, it will be only possible, in this general survey, to
notice those that mark the first steps of the invention, and the most
important of those that have accompanied its progress to the present
time.
The first method that suggested itself was to transmit signals by
means of pith-ball electrometers. When, for instance, two pith-balls
are suspended from a wire that is made to form part of an electric
circuit, the electricity communicated to the balls causes them to
diverge, and when the electricity in the wire is discharged, they
immediately collapse. This action of pith-balls, when electrified,
was the simplest mode known of making telegraphic signals, and it was
accordingly adopted by several of the early inventors of Electric
Telegraphs. The first person who proposed to apply it for that purpose
was M. Lesage, of Geneva, in 1774. His plan was to form 24 electric
circuits by as many separate wires, insulated from each other in glass
tubes; and to place in the circuit, at each communicating station,
an equal number of pith-ball electrometers. Each electrometer was to
represent a letter of the alphabet, and they were to be brought into
action by an excited glass rod. When a communication was to be made,
the wires connected with the separate galvanometers were to be charged
alternately with electricity by the excited rod of glass; and the
person at the receiving station, by noticing which of the electrometers
were successively put into action, could spell the words intended to be
communicated.
By the means thus proposed, correspondence could have taken place at
only short distances, for the charge of an excited glass rod would have
been too feeble to produce any sensible effect on the electrometers had
the length of the circuit been considerable. This difficulty might
have been overcome by substituting the charge of a Leyden jar for the
excited glass; but the more serious obstacle to the use of such a
telegraph would have been the cost, and the difficulty of insulating
the 24 wires required to work it.
Most of the early telegraphic inventors encumbered their inventions
with the same obstacle, as they seemed to consider it necessary to
have a separate circuit for each letter of the alphabet. It was not so
however, with all; for M. Lomond, a Frenchman, who ranks second in the
list of telegraphic inventors, modified the principle of M. Lesage, so
as to enable him to work with only two wires and one electrometer at
each station. With the experience since gained in the application of
the needle telegraph, such an arrangement seems very simple, and we are
inclined to wonder that it was not generally adopted, especially after
M. Lomond had shown the way.
To produce all the requisite signals with a single pith-ball
electrometer, it was necessary to vary the durations of each
divergence, and to combine several to form a single symbol. Thus,
suppose that a single divergence of the pith-balls for a second was
understood to signify the letter _A_; one divergence, followed by an
immediate collapse, by discharging the electricity, might signify _B_;
two prolonged divergences might signify _C_, and two short ones _D_;
and by thus increasing the number and varying the divergences of the
two pith-balls, all the letters of the alphabet might be indicated.
A still more direct method of representing the letters of the alphabet
was proposed by M. Reizen in 1794, by the application of the means
frequently adopted for exhibiting the light of the electric spark. The
charge of a Leyden jar was sent through strips of tin foil, pasted on
to a flat piece of glass, so as to form several lines, joined at the
ends alternately into a continuous circuit. Interruptions were made
in the foil by cutting small portions away, at which points brilliant
sparks appeared when the jar was discharged. As the interruptions
were so contrived as to form letters, and the strips of tin foil were
all arranged separately on a long pane of glass, any letter required
could be distinctly made visible by discharging the jar through that
particular circuit. To produce all the letters of the alphabet in this
manner, a separate circuit was required for each.
Another plan, far less feasible, and scarcely deserving of notice,
excepting for its peculiarity, was proposed in the following year
by M. Cavallo, who suggested the setting fire to combustibles, or
the explosion of detonating substances, as the means of signalling
intelligence. About the same time several attempts were made by
electricians in Spain to transmit signals by electricity, but their
plans were not more practicable than those already mentioned, and
depended for their effects on the discharge of Leyden jars.
The discovery of voltaic electricity at the beginning of the present
century was an important step in the progress of the Electric
Telegraph, though several years elapsed before the applicability of
the discovery for that purpose became known; and it was not fully
appreciated till within the last twenty years.
The electricity generated by the voltaic battery is far greater in
quantity than the most powerful electrical machine can excite, whilst
its intensity is so feeble that it cannot pass in a spark through the
smallest interval of air. It presents, therefore, much less difficulty
in the insulation of the wires than frictional electricity, whilst
the rapidity of its transmission is for practical purposes equally
efficient. The electricity generated by the voltaic battery being great
in quantity and feeble in intensity, it is capable also of effecting
chemical decomposition and of imparting magnetism, both of which
properties have proved eminently useful in perfecting the Electric
Telegraph.
The first application of voltaic electricity to telegraphic purposes
was made by Mr. Soemmering in 1809. The signals of his telegraph
consisted of the bubbles of gas arising from the decomposition of
water, during the action of the electric current. His apparatus
consisted of a small glass trough, filled with acidulated water,
through the bottom part of which were introduced several gold wires
corresponding to the letters of the alphabet. The instant that an
electric current was sent through any two of the wires, by making
connection with a voltaic battery at the transmitting instrument,
bubbles of hydrogen gas rose from one of the gold wires, and bubbles of
oxygen gas from another; and as the volume of hydrogen gas, liberated
during the decomposition of water, exceeds by sixteen times that of
the oxygen, it was easy to distinguish them. In this manner all the
letters of the alphabet could be indicated by using 24 wires. The
object of having gold wires in the decomposing trough was to prevent
the oxidation of the metal; for had copper, or any other metal that
combines with oxygen, been employed, the points of the wires would soon
have become corroded.
This telegraph of Soemmering's, though not adapted for practical
application in the form he presented it, on account of the number of
wires required for the purpose, was nevertheless superior to any that
had previously been invented; and by a little modification it might
have been made a perfect instrument, capable of transmitting messages
by means of only two wires. Such a modification of the instrument was
proposed by M. Schweigger, twenty years afterwards; the only thing
required being the adoption of a code of symbols, by means of which
all the letters might be indicated by combinations of the four primary
signals that are obtainable by two wires, as is at present done by the
needle telegraph in common use. At that time, however, the discovery of
the magnetic properties of the electric current, and other improvements
in the means of communicating, superseded for some years the use of
signals made by electro-chemical decomposition.
The next important step in the progress of telegraphic invention, after
that of Mr. Soemmering, was made by Mr. Ronalds, who in 1816 succeeded
in making a perfect apparatus, that transmitted every requisite signal
with the use of only a single circuit. In the agent employed, however,
there was a retrogression to frictional electricity and the pith-ball
electrometer, for at that time the property which a voltaic current
possesses of deflecting a magnetic needle had not been discovered.
Mr. Ronalds's plan was to have, at each communicating station, a good
clock with a light paper disc fixed on to the seconds wheel, on which
were marked all the letters of the alphabet, and the ten numerals. Only
so much of this disc was exposed to view as to show a single letter
at a time, through a small aperture, as the seconds wheel revolved.
The clocks at the corresponding stations were set exactly together, so
that the same letter was exposed to view at each instrument at the same
instant. A pith-ball electrometer, connected in a single circuit with
the transmitting station, was kept distended during the transmission
of a message by charging the wire from an electrical machine; and when
the letter required to be indicated appeared at the aperture of both
instruments, the operator at the transmitting instrument instantly
discharged the electricity of the wire by touching it, and thus
caused the pith-balls to collapse. In this manner the person at the
receiving station, by attentively watching the pith-balls, and noticing
the letter that appeared at the instant of collapse, could read the
messages signalled.
Mr. Ronalds so far perfected his invention, that it worked accurately,
though slowly, through eight miles of wire insulated in glass tubes.
Having thus succeeded in putting into action his single wire
telegraph, Mr. Ronalds sought the patronage of Government for its
practical adoption, such a notion as that of establishing a telegraph
for commercial purposes not being at that time entertained. For a
length of time his application received no attention, and when at
length the Lords of the Admiralty condescended to answer, they sent Mr.
Ronalds, as the reward for his ingenuity, and as compensation for the
time and money bestowed in perfecting the invention, the expression of
their opinion--that "telegraphs are of no use in time of peace, and
that during war the semaphore answered all required purposes"! This
reply, so characteristic of the manner in which Government _employés_
generally regard anything new to which their attention is solicited,
completely disheartened Mr. Ronalds. He abandoned the Electric
Telegraph to its fate; and having gone abroad, he returned some years
later to find that, notwithstanding the _dictum_ of the Lords of the
Admiralty, telegraphs are of great use in time of peace as well as
of war, and that the old semaphore had been entirely superseded by
the means of transmission he had indicated twenty years before. Mr.
Ronalds has since received a small pension, not however as a reward
for his ingenious telegraph invention, but for his services in other
departments of science.
The discovery of the magnetic property of an electric current by
Professor Œrsted, in 1818, was most important in the subsequent
progress of telegraphic invention, though it was not applied in a
practical manner till nearly twenty years afterwards. In 1820, indeed,
M. Ampère submitted to the Academy of Sciences at Paris a telegraphic
instrument for the transmission of signals by the deflection of
needles, but he adopted the impracticable plan of the earliest
inventors, of having a separate wire for each letter of the alphabet. A
much more important contribution to telegraphic invention by M. Ampère
was the discovery of electro-magnets, which act an important part in
many recent electric telegraphs.
As the magnetic properties of a voltaic current are extensively applied
in electric telegraphs, it is desirable briefly to explain the nature
of the action of voltaic batteries before proceeding farther with the
history of the invention.
To excite a current of voltaic electricity, it is usual to employ a
series of zinc and copper plates, arranged alternately in separate
jars; or, what is now most common, in cells of gutta percha, separated
from each other in a gutta percha trough. The cells are nearly filled
with diluted sulphuric acid, and a wire is attached to each end of
the trough; one being connected with the last zinc plate, and the
other with the last copper plate of the opposite ends of the trough.
When these wires are brought into contact, electricity is instantly
generated by the action of the acid on the zinc plates. The electricity
excited by the action on the zinc in one cell is carried on to the
next, and that again excites and transfers an additional quantity to
the third cell, thus increasing in intensity to the last pair of plates
in the series. The _electric current_, as it is called, passes along
the wire, and whether the wire be one yard, or whether it be a hundred
miles long, the generation of electricity takes place the instant
that the circuit is completed, and ends the instant that the circuit
is broken. There is this difference, however, in the transmission of
electricity through a long and through a short circuit, that in the
former case the increased resistance offered by the length of the wire
greatly diminishes the quantity of electricity transmitted though it
does not perceptibly retard the velocity.
When a balanced magnetic needle is held above a short thick copper wire
whilst it is transmitting an electric current, the needle is deflected
from its natural position, and inclines either to the right or to the
left, according to the direction in which the current passes. If, for
instance, the north pole of the needle be pointed towards the copper
pole of the battery, it will be deflected towards the east, but if
the direction of the battery current be reversed, the deflection will
be towards the west. The effect instantly ceases when the current is
interrupted by breaking connection with either pole of the battery. The
copper wire, though under ordinary circumstances incapable of being
rendered magnetic, thus becomes endowed with strong magnetic properties
when it is transmitting an electric current, and acts on the magnetic
needle in the same manner as if there were an immense number of small
magnets placed along the wire across its diameter.
The magnetic property of an electric current, first discovered by
Œrsted, was applied by M. Ampère to impart magnetism to iron, by
coiling a length of copper wire round a bar of iron, taking care to
cover the wire with an insulating substance, so that when an electric
current was transmitted the electricity might not pass through the
iron. Coils of copper wire, covered with cotton or silk, can thus
impart most powerful magnetism to a piece of soft iron; but it loses
its magnetic power the instant that the electric current is interrupted.
The effect of a coil of insulated wire in increasing the magnetic
power of an electric current, was applied by M. Schweigger in 1832
to increase the sensitiveness of a suspended magnetic needle. By
surrounding a compass needle with several convolutions of covered wire,
it was found that the deflections of the needle were much greater
and more active; and he thus showed the way to the construction of
those delicate galvanometers, which indicate by their deflections
the slightest disturbance of electrical equilibrium. Schweigger may,
therefore, be considered the original inventor of the Needle Telegraph;
and as he pointed out a method of impressing symbols on paper
mechanically, by means of electro-magnets, he may be considered also as
the original inventor of Recording Electric Telegraphs.
The first near approach to the needle telegraph, now used in this
country, was made by Baron de Schilling, who, in 1832, constructed
at St. Petersburg an electric telegraph consisting of five magnetic
needles. This may be considered as the precursor of the five-needle
telegraph, first patented by Professor Wheatstone in 1837. By the
separate deflection of those needles to the right hand or to the
left, by reversing the connections with the poles of the batteries,
ten primary signals could be obtained; and by bringing two into
action at the same time, many more signals might be made than were
required for indicating the letters of the alphabet, and they could
be appropriated to express several words. For the action of this very
efficient telegraph only five wires were required, and the signals
being all primary ones, the messages might have been transmitted very
quickly.[6] In a subsequent modification of the telegraph, he contrived
to make all the signals with one magnetic needle alone, by repeating
the deflections to the right and to the left, as done in the needle
telegraph now generally used in England.
Another step made by Baron de Schilling was the invention of an
alarum to call attention when a message was about to be sent. Some
contrivance of this kind was considered essential in the early days of
the practical application of the Electric Telegraph, as no one then
contemplated that telegraphic communications would be so frequent as
to require a person to be always near the instrument, waiting for the
receipt of messages.
Baron de Schilling's alarum was very simple. One of the magnetic
needles acted as a detent which held a weight suspended, and when
the needle was deflected, the weight fell upon a bell. The alarums
subsequently invented were constructed on the same principle, but
instead of employing one of the magnetic needles as a detent, an
electro-magnet was used for the purpose, and clock mechanism was
introduced to sound a bell continuously, as soon as it was set in
action by the withdrawal of the detent. At the present time alarums are
not used in the regular stations of the electric telegraph companies;
the sound of the needles, as they strike against the ivory rests on
each side, being sufficient to call the attention of the clerks, who
are in constant attendance.
We have hitherto been enabled to trace, step by step, the advances
made at intervals--years asunder--in bringing the Electric Telegraph
into practical use; but we are now approaching a time when it becomes
difficult to enumerate, and impossible to describe within reasonable
compass, the numerous inventions that were patented and otherwise made
known for giving greater efficiency to that means of communication.
In the early part of the year 1837, the electric telegraphs of Mr.
Alexander, of Edinburgh, and of Mr. Davy, were publicly exhibited
in London, and excited much attention; though, at that time it was
not supposed that it would be possible to make use of that means of
communication for general purposes. Mr. Alexander's telegraph was the
same in principle as those of M. Ampère and of Baron de Schilling,
though in some respects not so efficient as either, for its action was
slow, and it required a separate wire for each letter of the alphabet.
It was considered a great advantage of this telegraph at the time,
that it exhibited actual letters of the alphabet, instead of symbols.
This was effected by having the twenty-six letters painted on a board,
and concealed from view by a number of small paper screens, which were
attached to magnetic needles. When any of the needles was deflected
by sending an electric current through the surrounding coil, the
screen was withdrawn and exposed the letter behind. Twenty-six keys,
resembling those of a pianoforte, were ranged in connection, one with
each wire, and on pressing down any one of the keys, contact was made
between the battery and the wire connected with its associated magnetic
needle; and in this manner, messages might easily be transmitted
and read. The objections to this telegraph, in the form in which it
was exhibited, were not only the impracticability of laying down
and insulating so many wires, but the paper screens attached to the
needles impeded their action, and rendered the transmission a very slow
process. It is questionable, indeed, whether that telegraph could have
been worked at all through a circuit of many miles.
Mr. Davy's telegraph was similar to that of Mr. Alexander's, though
much more compact and better arrang
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