Transcribers' Note:
Greek transliterations were added by the transcribers and enclosed in {curly braces.}

GREAT FACTS.

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.]

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."

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.

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.

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.

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.

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.

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.

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.

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 d1 on both sides are reflected to form the single image d2, and the images e1 are in the same manner reflected to form the second image e2.

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.

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.

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.

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.

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.

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.

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.

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.

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.