Discoveries and Inventions of the Nineteenth Century

non-compound, 32,104 lbs.; or, the consumption of coal by the former was 28 lbs. per mile; by the latter, 36 lbs. per mile. This represents a saving of about 21 per cent. of the fuel. As the steam enters the high-pressure cylinder first, it would not be possible to start the engine if it had stopped at one of the “dead-points” on that side, without a special arrangement for admitting the steam directly to the other cylinder in such cases. This, of course, is required only for the first stroke, and Mr. Worsdell and M. von Borries have contrived for this purpose an ingenious valve, brought into operation when required by a touch from the engineer, and then immediately adjusting itself automatically, so as to restore the steam connections to their normal condition. PLATE II.NORTH EASTERN RAILWAY LOCOMOTIVE. Fig. 10a.—G.N.R. Express Passenger Locomotive. Another type of the high-speed passenger engines used for express trains on several of the great English railways is well represented by one of the Great Northern Company’s locomotives, as depicted in Fig. 10a. In this there are a single pair of driving wheels of very large diameter, namely, 8 ft. 2 in., so that each complete movement of the pistons will carry the engine forwards a length of nearly 26 ft. There are outside cylinders, and therefore the driving axle is straight, and the leading wheels are in two pairs, mounted on a bogie which is capable of a certain amount of independent horizontal rotation. The Stephenson’s link motion, described on page 17, has lately been often supplanted by another arrangement known as Joy’s valve gear, which leaves the crank axle unencumbered with eccentrics, and, as taking up less space, is generally now preferred for locomotives and also for marine engines. Its principle is very simple, and will be readily understood from the diagram in Fig. 10b, where c is the spindle of the slide-valves 20as in Fig. 5, but capable, we shall now suppose, of a horizontal movement only. Jointed to it at D is a rod D E attached to a block at E, which can move only within a slot in the strong bar E F in a circular segment, the centre of which is at D. The bar we suppose for the moment to be immovable, and disposed symmetrically to C D. Now let an alternate up and down motion along the circular segment be given to block E, and the effect will be to leave the centre, D, unchanged in position, and, therefore, in that case the valve will not be moved at all. Now this reciprocating movement is given to the block E by a system of levers (not here shown), jointed to the connecting-rod (K, Fig. 9) in such a manner that the rod D E is compelled to follow the movement of the connecting-rod, but the end E must always travel in the circular segment. We have hitherto supposed this segmental piece to be fixed, but the engineer has the power of so turning it as to tilt either the upper or lower part towards D. If, for instance, the guiding segment is fixed as at II, the block in rising will push in the valve-spindle, and in descending draw it out, as the length of the rod D E is invariable. But if the guides be turned over so as to bring F nearer D than E, the same movement of the block will give the reverse motions to the valve-spindle. Fig. 10b.—Joy’s Valve Gear. From the great rapidity with which the machinery of the locomotive moves, the different parts require to be carefully balanced in order to prevent dangerous oscillations. For example, the centrifugal force of the massive cranks, etc., is balanced by inserting between the spokes of the driving wheels certain counterpoises, the weights and positions of which are finally adjusted by trial. The engine is suspended by chains and set in motion, and a pencil attached to one corner of the frame marks on a horizontal card the form of the oscillation, usually by an oval figure. When the diameter of this figure is reduced to about 116 inch, the adjustment is considered complete. 21The power of a locomotive, of course, depends on the pressure of the steam and the size of the cylinder, &c.; but a very much lower limit than is imposed by these conditions is set to the power of the engine to draw loads by the adhesion between the driving wheels and the rails. By the term “adhesion,” which is commonly used in this case, nothing more is really meant than the friction between surfaces of iron. When the resistance of the load drawn is greater than this friction, the wheels turn round and slip on the rails without advancing. The adhesion depends upon the pressure between the surfaces, and upon their condition. It is greater in proportion as the weight supported by the driving-wheels is greater, and when the rails are clean and dry it is equal to from 15 to 20 per cent. of that part of the weight of the engine which rests on the driving-wheels; but when the rails are moist, or, as it is called, “greasy,” the tractive power may be only 5 per cent. of the weight; about one-tenth may be taken as an average. Suppose that 30 tons of the weight of a locomotive are supported by the driving-wheels, that locomotive could not be employed to drag a train of which the resistance would cause a greater pull upon the coupling-links of the tender than they would be subject to if they were used to suspend a weight of 3 tons. The number of pairs of wheels in a locomotive varies from two to five; most commonly there are three pairs; and one, two, or all, are driven by the engine, the wheels being coupled accordingly; very often two pairs are coupled. The pressure at which the steam is used in the locomotive is sometimes very considerable. A pressure equal to 180 lbs. on each square inch of the surface of the boiler is quite usual. The greater economy obtained by the employment of high-pressure steam acting expansively in the cylinder, points to the probability of much higher pressures being adopted. There is practically no limit but the power of the materials to resist enormous strains, and there is no reason, in the nature of things, why steam of even 500 lbs. per square inch should not be employed, if it were found otherwise desirable. It need hardly be said that locomotives are invariably constructed of the very best materials, and with workmanship of the most perfect kind. The boilers are always tested, by hydraulic pressure, to several times the amount of the highest pressure the steam is required to have, and great care is bestowed upon the construction of the safety-valves, so that the steam may blow off when the due amount of pressure is exceeded. The explosion of a locomotive is, considering the number of engines in constant use, a very rare occurrence, and is probably in all cases owing to the sudden generation of a large quantity of steam, and not to an excessive pressure produced gradually. Among the causes capable of producing explosive generation of steam may be mentioned the deposition of a hard crust of stony matter, derived from the water; this crust allows the boiler to be over-heated, and if water should then find its way into contact with the heated metal, a large quantity of steam will be abruptly generated. Or should the water in the boiler become too low, parts of the boiler may become so heated that on the admission of fresh water it would be suddenly converted into steam. When an explosion does take place, the enormous force of the agent we are dealing with when we bottle up steam in an iron vessel, is shown by the effects produced. Fig. 11 is from a photograph taken from an exploded locomotive, where we may see how the thick plates of iron have been torn like paper, and the tubes, rods, and levers of the engine twisted in inextricable confusion. Fig. 11.—Locomotive after Explosion. Fig. 12.—Hancock’s Steam Omnibus. Locomotive engines for propelling carriages on common roads were 22invented many years ago, by Gurney, Anderson, Scott Russell, Hancock, and others. One designed by Hancock is represented in Fig. 12. Such engines do not appear to have found much favour, though the idea has been successfully realized in the traction engines lately introduced. Probably the application of steam power to the propulsion of vehicles along common roads fell into neglect on account of the superior advantages of railways, but the common road locomotive is at present receiving some attention. In the tramways which are now laid along the main roads in most large cities we see one-half of the problem solved. It is not so much mechanical difficulties that stand in the way of this economical system of 23locomotion, as the prejudices and interests which have always to be overcome before the world can profit by new inventions. The engines can be made noiseless, emitting no visible steam or smoke, and they are under more perfect control than horses. But vestries and parochial authorities offer such objections as that horses would be frightened in the streets, if the engine made a noise; and if it did not, people would be liable to be run over, and the horses be as much startled as in the other case. But horses would soon become accustomed to the sight of a carriage moving without equine aid, however startling the matter might appear to them at first; and the objection urged against the noiseless engines might be alleged against wooden pavements, india-rubber tires, and many other improvements. It is highly probable that in the course of a few years the general adoption of steam-propelled vehicles will displace horses, at least upon tramways. The slowness with which inventions of undeniable utility and of proved advantage come into general use may be illustrated by the fact of some great English towns and centres of engineering industry not having made a single tramway until, in all the populous cities of the United States, and in almost every European capital, tramways had been in successful operation for many years. [1890.] Some time has elapsed since the foregoing paragraph was written for an earlier edition of this work, and during that period there has been an advance in both practice and opinion; so that now it has become highly probable that before the century ends a great change may be witnessed in our modes of locomotion, even on ordinary roads. Already every town of importance throughout the United Kingdom has been provided with excellent tramways, along which, in not a few instances, horseless vehicles roll smoothly, to the great convenience of the general public, while not one of the difficulties and dangers to general street traffic has been experienced that were so confidently predicted by those who were unable to perceive that an innovation might be an improvement. The now universally-popular bicycle has been continually receiving improvements, of which there appears to be no end, and as the machine and all the contrivances connected with it are so familiar to everyone, there is no need here to do more than to refer to them, because they have led the way to great improvements in ordinary carriages. The steam-propelled vehicle for common roads has just been mentioned as an invention belonging to the first half of the century, and the reasons it did not find favour have been alluded to. There exists in the United Kingdom a law concerning horseless carriages travelling on highways, which was passed to apply to traction engines, and enacts that other than horse vehicles are not to go along a road at a greater speed than four miles an hour, and only two miles an hour through a town, and moreover they are to be preceded by a man bearing a red flag, etc. But a bill has been introduced (1895) into the legislature to amend