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 forthe 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 applicationof 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 inboats 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 thewaste 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.
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 exceptionto 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 descendingsome 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 theoscillating 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 arrangementthat 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 locomotiveengines 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 asfollows:—
"Sufficient evidence has been adduced to convince yourCommittee—
"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 authorwas 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 fareswhich 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; andso 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 actionwas 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,ais the fire-box or furnace, surrounded on all sides with water, with the exception of the sideperforated for the reception of the tubes;bis the boiler;d, one of the steam cylinders;e, the chimney;handi, 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 averagespeed 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 theimportance 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 therails 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 someportion 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 formationof railways; and long before any connected system was completed in this country, thechemins de ferformed 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 whichhas 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 CivilEngineers:—
"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 railwayhad 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 tocold 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 ofconstruction 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.
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, afterwardsimproved 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 overan 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 sizeof 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; foras 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.
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 allphotographic 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"—thatignis fatuusof 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 yearsafterwards:—
"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 itwith 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 thiscase 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 beforeM. 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 hithertoproduced.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.