The tartaric acid and soda in the generator do not mingle with the water, and the tartrate of soda, resulting from the combination, is emptied after the soda-water is drawn off, before renewing the charge.
A French modification of this apparatus, in glassvessels protected by cane netting, called a "gasogene," has recently been introduced, and is extensively used. The materials for generating the carbonic acid gas are put into the smaller vessels, and kept separate until the apparatus is inverted, and then gas is rapidly generated, and forces itself through the water.
The powders that are sold for making soda-water, by mixing them together, consist of carbonate of soda and tartaric acid. When brought together in solution, a violent effervescence ensues, but the gas is not combined with the water in the same manner as when it is forced in and allowed to remain for some time with the liquid to be aerated. There is the further disadvantage attending such powders, that the tartrate of soda, formed by the tartaric acid and the carbonate of soda, employed to generate the gas, is drunk with the water.
"Is there anything whereof it may be said, See, this is new? it hath been already of old time, which was beforeus."18This observation of Solomon, the correctness of which we have often seen verified in this History of Inventions, is applicable even to that great apparent novelty the formidable "Revolver"—that death-dealing weapon, which will fire six shots in rapid succession by merely pulling the trigger so many times, as fast as it is possible.
The Revolver was almost unknown in this country until 1851, when it was brought prominently into notice at the Great Exhibition, by the specimens shown there by Colonel Colt, of the United States. Pistols with six barrels, which might be fired successively with the same lock, by turning them round, were, indeed, previously seen in gun-shops; but their clumsy form and their great weight prevented them from being used. Nor was Colonel Colt much more successful in his earlier attempts to bring his Revolver into public notice. He obtained his first patent inAmerica in 1835, and established a manufactory for the pistols at Paterson, United States, where he expended £35,000 in attempting to bring the fire-arm to perfection, but with no beneficial result to himself beyond gaining costly experience. He made further improvements in 1849, and so far perfected the weapon that it had been used extensively in America before it was brought into notice in this country.
When Colonel Colt came to England, he undertook to investigate the origin of repeating fire-arms, with a view to ascertain how far he had been anticipated; and the result of his researches was, that repeating fire-arms, similar in principle to his own Revolver, had been inventedfour centuries before.
He found in the Armoury of the Tower of London a matchlock gun, supposed to have been made as early as the fifteenth century, which very closely resembles, in the principle of its construction, the Revolver of the present day. It has a revolving breech with four chambers, mounted on an axis fixed parallel to the barrel, and on that axis it may be turned round, to bring any one of the four loaded chambers in succession in a line with the barrel, to be discharged through it. There are notches in a flange at the fore end of the revolving breech to receive the end of a spring, which is fixed to the stock of the gun, for the purpose of locking the breech when a chamber is brought round into the proper position. The hammer is split at the end, so as to clasp a match, and to carry its ignited end down to the priming powder when the trigger is pulled. Each chamber is providedwith a priming pan that is covered by a swing lid, and, before firing, the lid is pushed aside by the finger, to expose the priming powder to the action of the lighted match. If the date of this gun be correctly stated, a very rapid advance in the art of gunnery must have been made after the invention of gunpowder, which took place only one hundred years previously. The want of a better mode of discharging the gun than a lighted match was one of the chief obstacles to the introduction of the Revolver four centuries ago.
There is also in the Tower Armoury a specimen of a repeating fire-arm of a more recent date, though still very ancient, that presents considerable improvement on the preceding one. It has six chambers in the rotating breech, and is furnished with a barytes lock and one priming pan, to fire all the chambers. The priming pan is fitted with a sliding cover, and a vertical wheel with a serrated edge projects into it, nearly in contact with the powder in the pan. To this wheel a rapid motion is given by means of a trigger-spring, acting upon a lever attached to the axis of the wheel; and the teeth of the wheel strike against the barytes, which is brought down, previously to firing, into contact with it, and the sparks thus emitted set fire to the powder in the priming pan, and discharge the piece. In this instance, also, the breech is rotated by hand.
A still further advance towards perfection in repeating fire-arms is to be seen in the United Service Museum, where there is a pistol, supposed to havebeen made in the time of Charles I., with the breech rotated by mechanical means. In this pistol, the act of pulling back the hammer turns the breech, containing six chambers, one-sixth part of a revolution, and the priming powder is ignited by a flint hammer striking against steel.
The manufacture of these fire-arms presented some practical difficulties which could only be overcome by great care and skill in the construction; and from the failure in this respect they were not patronized. It was necessary, in the first place, that the loaded chambers should be brought into an exact line with the barrel, and be firmly retained there during the discharge. It also required great nicety in the fitting of the breech to the barrel, to prevent the fire from communicating to the other chambers. A further difficulty was to prevent the spindle, whereon the breech revolved, from becoming foul by the explosion of the powder; otherwise, after firing a few times it would stick fast, and the gun would become useless.
The earliest patent for repeating fire-arms in this country was obtained by James Puckle, in 1718, for a gun with a rotating breech. There were six chambers in the breech, which was turned round by a winch, and, when the six were fired, there was an arrangement by which the chambered breech could be removed, and another loaded one substituted for it. Mr. Puckle appears to have been of a poetical turn of mind, and the specification of his patent is enlivened by the following loyal couplet, which deserves to be quoted as a novelty in patentrecords:—
"Defending King George, our country and laws,Is defending yourselves and the Protestant cause."
"Defending King George, our country and laws,Is defending yourselves and the Protestant cause."
"Defending King George, our country and laws,Is defending yourselves and the Protestant cause."
The invention of percussion priming in 1800, by the Rev. A. J. Forsyth, was an important step towards the perfection of fire-arms generally, and of Revolvers in particular; for until the chambered breech could carry round with it in a compact form the priming for each chamber, the construction must have been clumsy, and the action uncertain.
Colonel Colt, as already stated, took out his first patent in 1835, and in 1849 he patented the improved Revolver, which he has brought into general use. It has six chambers in the rotating breech, and the nipples to hold the percussion caps are sunk into a recess, so that the lateral fire, if any, cannot reach them; and at the other end, the chambers are protected from lateral fire by chamfering their mouths. By these means, the danger of firing the gunpowder in the other chambers is effectually provided against.
The demand for Colt's Revolvers became so great after the last improvements were made, that at his manufactory, at Hartford, in America, he made 53,000 of them in 1853; and at his manufactory at Vauxhall, near London, he employs upwards of 300 workmen, though by far the largest portion of the work is done by machinery.
Several improvements have been introduced in Revolvers since Mr. Colt's patent of 1849, among which is the arrangement, made by Mr. Adams in 1851, for causing the chambered breech to turn by the action of pulling the trigger, which at the sametime draws back the hammer. By this arrangement, the whole of the six loaded chambers may be discharged in three seconds, whilst the pistol continues presented.
The latest improvements in Revolvers were contrived by Mr. Josiah Ells, of Pittsburg, North America, as specified in a patent obtained for him by the author, in his own name, in 1855. The annexed woodcuts show the figure of this Revolver, with the working parts round the lock exposed to view, together with the shape of the revolving chambered breech.
In this improved Revolver, the force required to pull back the hammer,a, is regulated by a doublespring,w, so as to diminish as the hammer is drawn back; and at the moment of firing a slight pull of the trigger is sufficient. Another improvement consists in the addition to the chambered breech,d, of a projecting tube, which prevents the spindle on which it turns from becoming foul; and there is also a safety bolt added, as a protection against accidental firing.
The plan of making the mere action of drawing the trigger turn the chambered breech and pull back the hammer, as originally contrived by Mr. Adams, required so much force to pull the trigger as to interfere materially with the accuracy of aim. There was danger, also, in that mode of turning the chambered breech, arising from premature firing. In Mr. Ells's Revolver these objections are in a great measure obviated; first, by the action of the double spring, by which the force required is diminished as the trigger is pulled farther back; and in the second place, by making the shoulder of the hammer catch into a small notch, which holds it at full cock, until, by a further pull of the trigger, the pistol is fired.
An improvement in the art of war, no less important than the Revolver, was introduced nearly at the same time. The Revolver affords a formidable means for attack or defence at short distances, whilst the Minié Rifle extends the destructive range of fire-arms far beyond the distance to which the ordinary musket ball could reach. The principle of rifling gun barrels was first made known in the specification of an invention patented in 1789, by Mr. Wilkinson, the improvement he effected being thus described:—"The gun, or piece of ordnance, after being bored in the usual method, hath cut therein two spiral grooves, which run the whole length of the bore. These curves, according to their curvature, will give a circular motion to the shot during its flight."
The spiral grooves, when the bullets are rammed down, cause the ball to offer greater resistance, therefore the explosive force of the gunpowder is brought to act upon them more completely before they leave the gun barrel; and the rotary motion imparts greater steadiness to the ball. Rifled barrels, therefore, carry the balls farther, and increase the accuracy of the aim. They, however, require increased power and longer time to ram down the ball in loading, and the risk of bursting the gun is increased if the ball be not rammed close upon the powder. For these reasons, they were considered unfit to be employed generally by soldiers, and they were entrusted only to select corps of rifle shooters. The object of Captain Minié's invention was to facilitate the loading of rifles, by contriving a bullet which might be easily rammed in, and would expand in the act of firing, so as to fill up the grooves. What is commonly called the Minié Rifle is, in fact, only a Minié Rifle Ball, for the barrels of the guns are nearly the same as the ordinary grooved rifles.
The ball is an elongated one, with a hollow cone at the bottom, into which is fixed an iron button. When the gun is fired, the button is forced into the cone, and expands the lead, which thus fills up the grooves and gives a spiral direction to the bullet.The Minié ball serves the purpose excellently for a short time, but after firing several rounds the iron button is forced through the lead, leaving a portion of it behind, which clogs up the barrel, and renders it unfit for use.
Several substitutes for iron were tried, to remove that inconvenience, and it was at length found that the button might be dispensed with altogether, for the hollow cone is of itself sufficient to expand the lead. The balls are, therefore, now made in that manner at the Government gun manufactory at Enfield, and the rifled guns now used in the army, which carry bullets to the distance of a mile and more, are called theEnfield Rifle. The cost of each of these rifles to the Government is stated to be £3 4s. 7½d. As the balls are made to slip into the barrels easily, they can be loaded as readily as the common musket: and they will carry three times the distance, with much more certainty.
Many ingenious men have vainly attempted to apply what has been erroneously called "centrifugal force" as a motive power, conceiving that the effort made by bodies to fly off when whirled round in a circle was occasioned by a force generated by their rotation. The experiment of the "whirling table," which is commonly shown to illustrate centrifugal action, tends to confirm the notion that force is generated; for it is there seen that, when the velocity of rotation is doubled, the centrifugal force is quadrupled, and that it continues to increase in a geometrical ratio. It has, therefore, been conceived that a power might be generated of indefinite amount; for as a double velocity can be communicated by doubling the moving power, whilst the tendency to fly off at the circumference is quadrupled, there appeared to be a creation of power which, if properly applied, would realize perpetual motion.
A working engineer known to the author was so fully possessed with the notion that power might thus be created, and that its application would be of the utmost benefit, that he imagined he had been speciallyappointed to reveal the principle to man, as a boon of inestimable value to the manufacturing arts. The plan he adopted was to employ what he called a generating engine, consisting of a centrifugal pump; and the force with which the water was projected from the ends of two rotating horizontal arms was directed against pistons working in cylinders, as the force of steam is in a steam engine. Having once set this machine in action, he expected to be able, by means of the self-creating centrifugal force, to generate the power that worked the generating engine, and thus to have a reservoir of force of any magnitude constantly at command. So completely satisfied was he of the practicability of the plan, founded, as he supposed, upon one of Newton's laws of motion, and he felt so happy in the thought of being charged with an important mission for the benefit of mankind, that it was almost cruel to attempt to correct his notions of the power of centrifugal force. He spent all his money in endeavouring to realize this impossible project, and even its failure did not convince him of his error.
The simple kind of Centrifugal Pump applied in that chimerical scheme was known upwards of one hundred years ago. It consisted of a vertical hollow shaft, into which were inserted two horizontal arms. The shaft was supported on a pivot at the bottom, and was turned by a handle at the top, as represented in the accompanying drawing. The lower end of the vertical shaft was immersed in water, and when rotary motion was given to the machine, the centrifugalaction propelled the water from the ends of the arms, and the water rose in the vertical shaft to supply its place.
The effect in a pump of this construction is due to the pressure of the atmosphere, for the outpouring of the water from the rotating arms tends to produce a vacuum in the shaft, in the same manner as the lifting of the plunger in a common pump. It is evident, therefore, that a Centrifugal Pump of that construction could not raise a column of water higher than the pressure of the atmosphere would force it up, which would be about thirty feet.
Mr. Appold's Centrifugal Pump, which constitutedone of the most remarkable features of the Machinery Department of the Great Exhibition, is constructed on a different plan, though the principle is the same. The rotating arms are immersed in the water to be raised, and to diminish the resistance which would be produced by the rotation in water of two or more exposed arms, they are enclosed within discs of metal, about one foot in diameter, and three or four inches apart. The arms are formed by curved partitions between the discs, which radiate from the centre to the outer rim, towards which the space betweenthe discs is contracted. This pump is fixed on an axis, to which rapid rotary motion can be given; and it is fitted into a case connected with the pipe that conveys the water to the discharging orifice. The water enters the rotating disc through a large aperture in the centre, and it is forced through the spaces formed by the radical arms with increasing velocity, until it escapes from the circumference. Sections of Mr. Appold's pump are shown in the accompanying diagrams, in which A is the central opening for the admission of water; C, C, C, the curved radical partitions which form the arms by which motion is communicated to the water, and through the ends of which it issues into the external case, connected with the lift-pipe, D.
In the Great Exhibition there were two other Centrifugal Pumps shown in action, one by Mr. Bessemer, and one by Mr. Gwynne, from America; but neither of them exhibited such striking effects as Mr. Appold's, which was so arranged as to throw out a continuous cascade of water from an aperture six feet wide, at a height of twenty-six feet. The Jury of Class V., who made numerous experiments to determine the practical efficiency of Centrifugal Pumps, and the relative merits of the three exhibited, reported very favourably of that of Mr. Appold, to whom a Council Medal was awarded. When rotating at the rate of 788 revolutions in a minute, and lifting the water 19·4 feet, the greatest practical effect, compared with the power employed, was attained. The discharge of water per minute at that height, with thepump rotating with a velocity of 788 revolutions, was 1,236 gallons; and with a lift of 8 feet, 2,100 gallons per minute were discharged, when the rotating velocity was 828 revolutions per minute. In Mr. Gwynne's and Mr. Bessemer's pumps, which had straight vanes, the ratio of power to the effect did not exceed 0·19. One of Mr. Appold's pumps, only one inch in diameter (the exact size of the small diagram), will discharge ten gallons per minute. The greatest height to which water has been raised by the pumps that are one foot in diameter is 67·7 feet, with a velocity of 4,153 feet per minute.
The velocity with which the pump should revolve depends upon the height to which the water is to be raised. Beyond a certain height, the required velocity is practically unattainable, but long before that limit is reached the waste of power becomes so great, that the pump is of no value, for the pressure on the circumference counteracts the force with which the water is expelled. It is, therefore, only at comparatively low levels that the Centrifugal Pump is a useful engine. The absence of all valves renders it very suitable for draining marshes, and for other similar purposes, as the muddy water and suspended matters will not obstruct its action.
In the Report of the Jury the influence of the curved shape of the radial arms is considered very important in producing the effects. "If the vanes be straight," the Report observes, "it is evident, that whatever may be the velocity of the water in the direction of a radius, when it leaves the wheel its velocityin the direction of a tangent will be that of the circumference of the wheel, so that the greater the velocity of the wheel the greater will be the amount ofvis vivaremaining in the water when discharged, and the greater the amount of power uselessly expended to create thatvis viva. If, however, the vanes be curved backwards as regards the motion of the wheel, so as to have nearly the direction of a tangent to the circumference of the wheel at the points where they intersect it, the velocity due to the centrifugal force of the water carrying over the surface of the vane in the opposite direction to that in which the wheel is moving, and nearly in the direction of a tangent to the circumference, will—if this velocity of the water over the vane in the one direction be equal to that in which the vane is itself moving in the other—produce a state of absolute rest in the water, and entire exhaustion ofvis viva." It is an interesting fact in the history of the invention, that the curved form was formerly adopted in some of the American pumps, and afterwards abandoned.
There are competing claims to the invention of Centrifugal Pumps in the form now adopted. This kind of pump is stated to have been used in America in 1830. M. Charles Combe took out a patent in France for a similar pump in 1838; but though Mr. Appold was later in the field with his more perfect machine, he appears to have proceeded independently of previous inventors.
No sooner had the formation of railways commenced for carrying passengers in long trains of carriages drawn by heavy locomotive engines, than the want was experienced of some different kind of bridge from any then existing for crossing rivers, roads, and valleys. The train could not be turned sharply round a curve to cross a road at right angles; and to make the requisite bend to enable it to do so would have taken the railway considerably out of its direct course. To overcome this difficulty "skew bridges" were designed, that crossed roads and canals in slanting directions. Iron girder bridges were also constructed, and thus the railway trains were carried across roads and narrow rivers at any required inclination, supported on flat beams of iron. Suspension bridges were found to be unfitted, on account of their oscillation, for the passage of locomotive engines; therefore, when it became necessary to carry railways across arms of the sea, or wide navigable rivers, at heights sufficient to allow the largest ships to pass underneath, neither girder bridges nor suspension bridges were suited for the purpose. Then arose the necessity of contriving some form of bridge of extensivespan that would be sufficiently strong and rigid for railway trains to pass over them in safety.
The Britannia Bridge, across the Menai Straits, was a triumphant response to the call for a new kind of suspended roadway adapted to the requirements of railways. The tubular principle of construction, designed by Mr. Robert Stephenson, was practically tested by Mr. Fairbairn; and the result of numerous experiments on the strength of iron, in different forms and combinations, established the soundness of that principle. The rigidity and strength of the Britannia Bridge depend on cellular cavities at the top and bottom, which, acting as so many tubes, give stability to the riveted plates of iron, and enable the bridge to bear the immense pressure and vibration of a heavy railway train without deflecting more than half an inch.
It was Mr. Stephenson's original intention to make a circular or oval tube, suspended by chains, for the trains to run through; but Mr. Fairbairn's experiments proved that a rectangular shape is stronger, provided the top and bottom, which bear the greatest part of the strain, are made rigid, either by additional plates of iron, or by tubes. The notion of a circular tube was, therefore, abandoned, and the rectangular form, with cells at the top and bottom, was adopted; first for the railway bridge at Conway, and afterwards for the much greater work across the Menai Straits.
It has been stated by Mr. Stephenson, that the idea of forming a tubular bridge was suggested by experience gained in constructing the railway bridgeat Ware, which consisted of a wrought-iron cellular platform; but a more exact representation of the principle on which the Britannia Bridge is constructed had been long previously seen across the Rhine, at Schauffhausen, where a rectangular tube, or hollow girder, made of wood, was erected in 1757. That bridge, though of different material, was in its principle of construction similar to the iron tubular bridges at Conway and at the Menai Straits. Another similar bridge, carried over the river Limmat, at Wettingen, constructed in 1778, had a span of 390 feet; and that, as well as the former, was raised to its position in one piece, by means of powerful screw-jaws. These curious and interesting structures, which may be considered the forerunners of the gigantic iron Tubular Bridges of the present day, were burnt by the French in 1799.
In constructing the Britannia Bridge, Mr. Stephenson took advantage of a rock midway from shore to shore, whereon to erect the central pier. Two other piers, at a distance, on each side, of 460 feet, were built without much difficulty in shallower water, and between these and the masonry on each side was a distance of 230 feet. There are eight rectangular tubes resting on those piers, to form two lines of railway, each tube being 28 feet high and 14 feet wide, exclusive of the cellular cavities at the top and bottom. These cavities are rectangular, and extend from one end of the bridge to the other, and may be regarded as long tubes. There are eight of them at the top, each 1 foot 9 inches square, and there are sixat the bottom, the latter being 2 feet 4 inches wide, and the same depth as those at the top. Sound is conveyed through these cavities as readily as through speaking tubes, and conversation can be thus easily carried on across the Straits.
The height of the central pier of the Britannia Bridge, from the foundation to the top, is 230 feet; and the height of the roadway above high water mark is 104 feet. The length of the large tubes, through which the railway carriages pass, on each side of the central pier, is 460 feet: and the total length from shore to shore, 1,531 feet. The tubes are connected together at the piers to give the bridge additional strength, and they are composed altogether of 186,000 separate pieces of iron, which were pierced with seven millions of holes, and united together by upwards of two millions of rivets. The whole mass of iron employed weighed 10,540 tons.
The Britannia Bridge was commenced in May, 1846, and the first of the main tubes was completed in June, 1849. The work was carried on close to the bridge, on the Anglesea shore; and when the tube was ready to be transported to its place on the piers, which had been prepared to receive it, eight flat-bottomed pontoons were provided to carry it, which, being brought underneath, floated the ponderous mass on the water as they rose with the tide.
The floating and fixing in its place of the tube took place on the 27th of the same month, in view of an immense concourse of spectators. After the preliminary arrangements for letting go had beencompleted, Mr. Stephenson, and other engineers, got on the tube, with Captain Claxton, R. N., to whom the management of the floating was entrusted. A correspondent of theIllustrated London Newsthus describes the proceeding, and its successful result:—"Captain Claxton was easily distinguished by his speaking trumpet, and there were also men to hold the letters which indicated the different capstans, so that no mistake could occur as to which capstan should be worked; and flags, red, blue, and white, signified what particular movement should be made. About 7.30 p.m. the first perceptible motion, which indicated that the tide was lifting the mass, was observed, and at Mr. Stephenson's desire, the depth of water was ascertained, and the exact time noted. In a few minutes the motion was plainly visible, the tube being fairly moved forward some inches. This moment was one of intense interest, the huge bulk gliding as gently and easily forward as if she had been but a small boat. The spectators seemed spellbound, for no shouts or exclamations were heard, as all watched anxiously the silent course of the heavily freighted pontoons. The only sounds heard were the shouts of Captain Claxton, as he gave directions to 'let go ropes,' to 'haul in faster,' &c.; and 'broadside on,' the tube floated majestically in the centre of the stream. I then left my station, and ran to the entrance of the works, where I got into a boat, and bade the men pull out as far as they could into the middle of the Straits. This was no easy task, the tide running strong; but it afforded me several splendidviews of the floating mass, and one was especially fine; the tube coming direct on through the stream—the distant hills covered with trees, two or three small vessels and a steamer, its smoke blending well with the scene, forming a capital background; whilst on one side, in long stretching perspective, stood the three unfinished tubes, destined ere long to form, with the one then speeding on its journey, one grand and unique roadway. It was impossible to see this grand and imposing sight, and not to feel its singleness, if we may so speak. Anything so mighty of its kind had never been before: again it would assuredly be; but it was like the first voyage made by the first steam-vessel—something until then unique. At 8.35 the tube was nearing the Anglesea pier, and at this moment the expectation of the spectators was greatly increased, as the tube was so near its destination: and soon all fears were dispelled, as the Anglesea end of the tube passed beyond the pier, and then the Britannia pier end neared its appointed spot, and it was instantly drawn back close to the recess, so as to rest on the bearing intended for it. There was then a pause for a few minutes, while waiting for the tide to turn: and when that took place, the huge bulk floated gently into its place on the Anglesea pier, rested on the bearing there, and was instantly made fast, so that it could not move again. The cheering, till now subdued, was loud and hearty, and some pieces of cannon on the shore gave token, by their loud booming, that the great task of the day was done."
The tube, when in position, was lowered down upon its bearings on the pier by opening valves in the pontoons, which thus sunk sufficiently to ease them of their load.
The work of raising the tube to its position, 100 feet above high water mark, was a much slower operation, and was attended with serious difficulties. Hydraulic presses were used for the purpose, placed at the top of the piers; two smaller ones, which had served to raise the Conway Bridge, being at one end, and a much larger press, made for the occasion, being fixed at the other. The immense tube was lifted by chains fixed to the heads of the presses, and two steam engines, of 40-horse power each, were employed to force the water into the cylinders. The diameter of the ram of the largest hydraulic press was 20 inches, and the pressure upon it was equal to 2¼ tons on each circular inch. The tube was raised by successive lifts of 6 feet each, and, as it was lifted, the space was built in with masonry for its ultimate bearing. During the operation of lifting, the bottom of the cylinder of the large hydraulic press burst out, and fell on the top of the tube, in which it made a considerable indentation. Mr. Stephenson had provided against the possibility of such accident, by having blocks of wood, an inch thick, introduced under the tube as it was elevated, and these blocks arrested its fall, or it would otherwise have been dashed to pieces. Even the small fall of an inch did considerable injury. This accident caused some delay, but the other tubes were in the meantime progressing, and the completed bridgewas opened for public traffic on the 21st of October, 1850.
The strength of the bridge was tested before passenger trains were allowed to pass through it, by placing in the centre of the longest tubes twenty-eight waggons, loaded with 280 tons of coal, and two locomotives, and by afterwards sending those heavy trains through the bridge at full speed. The deflection of the tubes in the centre amounted to only three-quarters of an inch in each cell; it being rather less when the trains were at full speed than when stationary. The strongest gusts of wind to which the bridge has been exposed have not caused a vibration of more than one inch. The total cost of construction was £601,865; of which sum £3,986 was for experiments, and £158,704 for masonry.
Another Tubular Bridge of rival magnitude to the one across the Menai Straits is now in the course of construction by Mr. Brunel across the Tamar, at Saltash, for the South Devon and Cornwall Railway. As no rock presented itself conveniently halfway across whereon to erect the central pier, Mr. Brunel was obliged to work at a great depth below the surface of the water in making the foundation of the Royal Albert Bridge. In the plan of making the foundation, as well as in the structure of the bridge itself, Mr. Brunel adopted a course altogether original. Instead of attempting to construct a coffer-dam by piles, which would have been almost impracticable at such a depth, and very costly, he caused a large iron tube to be put together, thirty-six feet in diameter, andninety-six feet long, to reach to the bed of the river. This monster tube was lowered perpendicularly in the middle of the river, and the water being pumped out of it, the men could work at the bottom in safety. In this manner, after much labour, the rock was prepared to receive the blocks of granite, which were laid one on the other, till they rose above the surface of the water. On that granite pedestal a cast-iron pier was raised to a height of 100 feet, the level of the roadway of the rails.
The cast-iron pier consists of four octagon columns, 10 feet in diameter. They stand about 10 feet apart, forming a square, and they are bound together by massive lattice-work of wrought iron, to prevent any lateral movement. Each of these columns weighs 150 tons; and when the full weight of the bridge rests on the foundation of the central pier, the pressure will be equal to 8 tons on the square foot, or double the pressure of the Victoria Tower on its base.
In the structure of the bridge, Mr. Brunel availed himself of the results of the experiments made by Mr. Fairbairn on the strength of iron tubes, but he adopted a very different plan from that of Mr. Stephenson. Instead of constructing a large tube for the trains to pass through, Mr. Brunel made tubular arches, consisting of iron plates curved and riveted together, to serve as rigid supports, from which the roadway is suspended by chains and by connecting iron bars.
The placing of the first of the tubular arches in position between the pier near the shore at Saltash and the central pier, which took place on the 1st ofSeptember, 1857, excited great interest, and at least 50,000 persons were assembled from places far and near to witness the operation. The tube, with the roadway and suspension chains, was floated from the yard where it was put together on four pontoons; and it was thus conveyed, and safely deposited on the piers at a height of 30 feet above high water mark. It was afterwards gradually raised by hydraulic presses to the top, a height of 100 feet. The work of raising it commenced on the 25th of November, and was completed on the 19th of May last.
The following lively description of the Royal Albert Bridge, and its surrounding scenery, extracted from a recent article in theTimes, gives a very good idea of the magnitude of the structure, by comparison with well-known objects:—"Though, probably, our readers may care little and have heard less about Saltash proper, it is likely henceforth to receive a fair share of general attention, and we can safely say, to those who will journey down to see the bridge, that the viaduct requires indeed to be a fine one to attract their attention from the lovely scenery of the valley of the Tamar, which it crosses. The banks of this noble river narrow in considerably as the stream reaches Saltash, and, hemmed in there to half a mile or so, suddenly widens out into as fine a sheet of water as any of its kind in the kingdom, its distant banks covered with cottages, and fringed with undulating woodlands down to the very edge. Across this narrow part of the channel, where Saltash, in picturesque dirt and disarray, straggles up the banks on one side,and a steep hill, covered with rock and rock-grown underwood, forms the other, the viaduct stretches high in air. The briefest general way of describing it is to say that it consists of nineteen spans or arches, seventeen of which are wider than the widest arches of Westminster Bridge; and two, resting on a single cast-iron pier of four columns in the centre of the river, span the whole stream at one gigantic leap of 910 feet, or a longer distance than the breadth of the Thames at Westminster. The total length of the structure from end to end is 2,240 feet,—very nearly half a mile, and 300 feet longer than the entire stretch of the Britannia Bridge. The greatest width is only 30 feet at basement; its greatest height from foundation to summit no less than 260 feet, or 50 feet higher than the summit of the Monument. The Britannia Bridge, both in size, purpose, and engineering importance, seems to offer the best comparison with that of Saltash, but the similarity between the structures is far from being as great as might be at first supposed. The Britannia tube is smaller, and cost nearly four times the price of the Saltash Viaduct, though the engineers had natural facilities which Mr. Brunel, for his Cornish bridge, certainly had not."
The form of the tubes is an oval, 17 feet in its longest diameter, and 12 feet in its shortest. They are bent into an elliptical curve, with a rise in the middle of twenty-eight feet. With the roadway and suspension chains attached, each tube weighs 1,100 tons. The total weight of wrought iron in the bridge, when completed, will be 2,650 tons; of cast iron,1,200; of masonry and brickwork there will be about 17,000 cubic yards; and of timber, about 14,000 cubic feet.
The second tube, which is in every respect like the first, was completed on the 30th of June last, and on the 10th of July was successfully placed in position between the central pier and the Devonshire side of the river. The operation of elevating it began on the 9th of August, and it has now reached nearly the level of the first one, the tube being raised six feet in a week.
The engraving on the other side is a view of this wonderful structure in its completed form. Its appearance is far more light and elegant than that of the Britannia Bridge, but it remains to be seen whether it will be equally steady under a gale of wind, and whether any vibration of the suspended roadway will interfere with the rapid motion of the trains. As the South Devon Railway has only one line of rails for the greater portion of its length, but a single roadway is provided on the Royal Albert Bridge.
The progress of railway locomotion has not only given rise to the construction of new kinds of bridges, but it has directed mechanical science to devise better means of applying the strength of materials. On the South Devon and Cornwall Railways are to be seen wooden viaducts, carrying the line over valleys at great heights, constructed with such slender timbers, that, to an inexperienced eye, they seem frightfully frail for the support of heavy railway trains.
ROYAL ALBERT BRIDGE, OVER THE TAMAR, AT SALTASH.
ROYAL ALBERT BRIDGE, OVER THE TAMAR, AT SALTASH.
We must not omit to notice, among the remarkablebridge erections connected with railways, the viaduct across the valley of the Boyne, which passes over the river close to the town of Drogheda, at a height of 95 feet. The central portion of the viaduct is supported on four piers, 90 feet above high water mark, with a span in the centre of 250 feet, and on each side of 125 feet. This elevated portion of the work is approached on the southern side by twelve arches, of 60 feet span each, and on the north by three similar arches. The viaduct is constructed of limestone and iron lattice-work, and is calculated to bear 7,200 tons.
During the erection of this viaduct the railway trains were carried over the valley on a wooden platform, without side railings, supported by scaffold-poles; and the crackling of the timbers, as the carriages passed over it, and the dizzy height at which they were carried through the air, produced a sensation of terror in nervous passengers, that was fully justified by the apparent danger.
The manufacturing progress of this country has depended, in a great degree, on the facility possessed of making machinery of all kinds by the aid of powerful engines worked by steam power. These engines, most of which appear to be self-acting, forge and roll and cut and bore beams of iron, boiler plates, and cylinders of immense size, which it would be impossible to make by hand; and they do the work with a rapidity and mechanical accuracy that would be otherwise unattainable. In the progress of manufacturing invention, the small steam engine first made by manual labour created the power to make other steam engines of large size; and those more powerful engines supplied the means of making still larger shafts and cylinders for engines that were to be employed in the construction of machines of various kinds, to be worked by the power thus accumulated.
The important advantages derived from the invention and application of self-acting machinery, not only by the community at large, but even by the workmen whose labour they for a time superseded, were forcibly stated by Mr. Whitworth, in his opening address atthe Institution of Mechanical Engineers, in September, 1856:—"I congratulate you," he observed, "on the success which in our time the mechanical arts have obtained, and the high consideration in which they are held. Inventors are not now persecuted, as formerly, by those who fancied that their inventions and discoveries were prejudicial to the general interest, and calculated to deprive labour of its fair reward. Some of us are old enough to remember the hostility manifested to the working of the power-loom, the self-acting mule, the machinery for shearing woollen cloth, the thrashing machine, and many others. Now the introduction of reaping and mowing machines, and other improved agricultural machinery, is not opposed. Indeed, it must be obvious, to reflecting minds, that the increased luxuries and comforts which all more or less enjoy, are derived from the numerous recent mechanical appliances and the productions of our manufactories. That of our cotton has increased during the last few years in a wonderful degree. In 1824, a gentleman with whom I am acquainted sold on one occasion 100,000 pieces of 74-reed printing cloth at 30s. 6d. per piece of 29 yards long; the same description of cloth he sold last week at 3s. 9d. One of the most striking instances I know of the vast superiority of machinery over simple instruments used by hand, is in the manufacture of lace, when one man, with a machine, does the work of 8,000 lace makers on the cushion. In spinning fine numbers of yarn, a workman in a self-acting mule will do the work of 3,000 hand-spinners with the distaff and spindle.
"Comparatively few persons, perhaps, are aware of the increase of production in our life-time. Thirty years ago, the cost of labour for turning a surface of cast iron, by chipping and filing with the hand, was 12s. per square foot—the same work is now done by the planing machine at a cost for labour of less than one penny per square foot: and this, as you know, is one of the most important operations in mechanics; it is, therefore, well adapted to illustrate what our progress has been. At the same time that this increased production is taking place, the fixed capital of the country is, as a necessary consequence, augmented; for in the case I have mentioned, of chipping and filing by the hand, when the cost of labour was 12s. per foot, the capital required for tools for one workman was only a few shillings; but now, the labour being lowered to a penny per foot, a capital in planing machines for the workman is required which often amounts to £500, and in some cases more."
Notwithstanding the great economy of labour by the self-acting machines now employed for doing all kinds of work, it is gratifying to find that it has not had the effect of throwing men out of employ; for the increased demand, consequent on the facility of production, has more than compensated for the substitution of automaton mechanism for handicraft.
It is extremely interesting to visit a large engineering factory, and to witness the ease with which the masses of crude metal are wrought in various ways, and converted by a number of seemingly self-acting engines into other engines and machines which are,in their turn, to become the agents of the further development of the skill and ingenuity of man. In the new Government factory at Keyham, near Devonport, which we believe to be one of the largest establishments of the kind in the world, most of those powerful engines of the best construction may be seen in operation. The completeness of the arrangements redounds much to the credit of Mr. Trickett, the chief engineer, under whose supervision they were made; and a walk through the factory, which is thrown open to public inspection, will well repay a journey of many miles. A detailed description of all its machinery would fill a volume, but we must now limit ourselves to a bare enumeration of some of the most remarkable features.
Numerous machines of the largest size, placed under the cover of an extensive and lofty roof, are employed in doing everything requisite for the fitting out of the largest steam-ships in the British navy. Shears, put in continuous motion by steam power, are seen moving steadily up and down, and cutting through the thickest boiler plates without the least apparent effort, the chisel-shaped knives that cut the metal moving just the same whether they be dividing the air or shearing iron. Punching engines, in like manner, force holes through iron plates an inch thick. Shaping and planing machines pare off the tough iron as if it were not harder than cheese. Riveting machines of different kinds bind together the plates of monster boilers with marvellous rapidity; whilst machines for boring, for drilling, for forging, and fordoing every variety of smaller work, are to be seen in operation in various parts of the factory.
Among the smaller self-acting engines, the forging machine for making bolts attracts attention by the rapidity of its action. It consists of a series of hammers placed side by side, so constructed as to shape small bars of iron into any required form, according to the mould of the swages beneath them, representing miniature anvils. It is interesting to watch how readily the hot iron receives its shape under the action of the hammers, which make about 700 strokes per minute, the work being transferred from one to another to be progressively finished. There is a circular saw that cuts through bars of iron as thick as railway rails, by making upwards of 1,000 revolutions per minute. A rivet-making machine forms the rivet, and shapes the head to the requisite size, with great accuracy and quickness. There are compound drilling machines, in which six drills are acting simultaneously; hydraulic presses, that force parts of machines together, and a great variety of other engines for the saving of time and labour.
Not the least curious of the smaller contrivances is an apparatus which deserves notice as a useful application of magnetism to manufacturing purposes. Several horse-shoe magnets are attached to two endless chains, moving over suitable wheels, and inclined at an angle of 30 degrees. These magnets at the lower end of the chain, dip into a tub containing the mixed brass and iron turnings and filings from the lathes and other tools, and the pieces of iron, beingattracted by the magnets, are carried away and brushed off into a box, leaving the brass behind to be remelted.
In one department of the building are immense foundry furnaces, where metals are melted and cast, the blast of the fires being maintained by large rotating fans, kept in action by a powerful steam engine, by which also the other machines are worked. The foundry is most conveniently contrived for casting works of any required size, fixed and travelling cranes being so stationed and arranged as to carry the ladles of liquid metal to any part of the floor.
In another department is the smithy, where the iron to be wrought into shape is heated in forges; and near to the forges stand the Steam-Hammers—those gigantic Cyclops of modern times, that strike blows, compared with the force of which the blows of the fabled Cyclops of antiquity were but as the fall of a feather.
Ranged in a row there are four of these ponderous engines, of various sizes; the largest hammer being so heavy as to require the power of four tons to lift it, and when falling from a height of 6 feet nothing can withstand its crushing blow. Yet the force of this mighty giant is so completely under control, and may be brought to act so gently, as scarcely to crack a nut placed to receive its fall.
The invention of the steam-hammer was the result of necessity. The shaft of a steam engine having to be made larger than usual, no hammer then in action by water power was capable of forging it, and Mr.James Nasmyth was applied to, to give his aid in contriving the means of removing the difficulty. It was then that the idea of lifting the hammer-block by the direct action of steam occurred to him, and by a succession of extremely ingenious devices, he at length perfected the steam-hammer, which has been pronounced to be one of the most perfect artificial machines, and one of the noblest triumphs of mind over matter that modern English engineers have yet developed.
The accompanying woodcut represents the largest of the four steam-hammers in Keyham factory. The hammer-block,a, weighing four tons, is guided in its ascent and fall by grooves in two massive uprights, which hold the whole together. The hammer-block is lifted by the piston-rod of the steam cylinder above it, which is made of such diameter, that the pressure of the steam on the surface of the piston may considerably overbalance the weight of the hammer-block, and overcome the friction of the connecting mechanism. The cylinder of the largest steam-hammer at Keyham is 18 inches diameter, which gives an area of 254 square inches; and the pressure of the steam generally used being fifty pounds on the square inch, the total steam pressure tending to force the piston up, when the whole of it is brought to bear, is equal to five tons and a half. The force of the blow of the hammer, when falling from its greatest height, is equal to 144 tons.
By the arrangements of levers, screws, and pipes and valves, shown in the engraving, the steam is firstadmitted under the piston, and thus acts directly in forcing it up, with the heavy hammer-block attached to the piston rod. When the block has been raised to the required height, it strikes against the end of a lever, which then shuts off the steam, and allows it to escape; whereupon the hammer falls with its full force vertically on the anvil. The end of the leverwhich turns off the steam may be adjusted at any height, according to the required force of the blow, so that the hammer may fall from a height of six feet, or be merely raised a few inches.