146 ADHESION OF THE WHEELS TO THE RAILS. machine being placed on a railway, and a chain applied to the back part of it, for the purpose of raising a weight as the engine was advancing, it was found that with steam equal to forty or forty-five pounds' pressure on the square inch, the engine was propelled at the rate of two miles and a half per hour, and raised perpendicularly 812 lbs. at the same speed; thus making the whole power equal to 896 lbs. at two miles and a half per hour, or nearly that of six horses. 107. Adhesion of the Wheels to the Rails.-The contrivances mentioned in the preceding paragraph were abandoned at this period, as it was now ascertained that there is sufficient adhesion between the wheels and the rails to propel an engine with a heavy load of carriages, along a road which is level, or moderately inclined, without any aid whatever. By experiments on the Wylam railroad, Mr. Blackett found that the adhesion was sufficient for the purpose in all kinds of weather, except when the surface of the rails was covered with snow; that, when the surfaces of the rails, and of the wheels, are either quite dry, or completely wet, the adhesion is the greatest, the surface being then most free from all extraneous matters; that when the rails, on the contrary, are moistened with wet, and partially covered with mud, the adhesion is the least; and that, in all the intermediate states of the rail, the adhesion becomes greater or less, according as its state approximates, more or less, towards either of these conditions. The experiments, by which the amount of adhesion was determined, are described in Wood's Treatise on Railroads. The author of this valuable work, on reviewing these experiments, considers the adhesion, exclusive of the power requisite to drive the engine itself, in the best or modern machines, as equal to the one-fifteenth part of the insistent weight; and in the common engines, working with vertical cylinders, as equal to the twentieth part of the weight, pressing on the rails by the driving wheels. 108. Stephenson's Killingworth Engine.-The amount of adhesion between the wheels and the rails having been deter STEPHENSON'S KILLINGWORTH ENGINE. 147 mined, it is interesting to trace the methods by which the power of the engine was communicated to the wheels, and the progressive motion of the machine effected. In 1814, Mr. George Stephenson constructed an engine for the Killingworth colliery; it had a cylindrical boiler, with a tubular flue passing through it, and two cylinders. The mode by which it was propelled is shown in the subjoined figure. B B Fig. 61, A A are the wheels of the carriage, supporting the engine; B B is the frame of the engine, supporting the boiler; a b and c d are connecting-rods, by which motion is communicated from the piston-rod to the crank, as in the fig. p. 148; be and d f are the cranks which turn the two cog-wheels e and f; the cranks are so adjusted as to be at right angles to each other, so that when one of them is at the stationary points, the other is at the points of its most energetic action (see pp. 55, 56); and this adjustment is secured by the interposition of another cog-wheel g, of the same size, which works into the two cog-wheels e and f. Two larger cogwheels K K are fixed upon the axles of the carriage wheels; the smaller cog-wheels turn the larger cog-wheels, and these, as they revolve, turn the driving wheels of the engine at the same time. This engine was found to draw after it, on a rail with an acclivity of about one yard in 450, eight loaded carriages, weighing altogether about 30 tons, exclusive of its own weight, at the rate of four miles per hour. 148 IMPROVED KILLINGWORTH ENGINE. 109. Improved Form of the Killingworth Engine.-In 1815, a patent was obtained by Messrs. Stephenson and Dodd for an improved form of the engine, in which it was proposed to get rid of the jerking motion, and other inconveniences caused by the cog-wheels. With this view, the crank-pin is connected immediately with one of the spokes of the engine wheels, by means of a ball-and-socket joint. In the following figure, A represents the cylindrical boiler; C C the two cylinders; at the top of each of the piston-rods is a transverse rod, to either extremity of which is fixed a connecting-rod; the connecting-rods are seen attached at F and G to one of the spokes of the driving wheels. The action of these cranks is maintained at right angles to each other, by means of an endless chain, which was made to pass over a toothed wheel, D and F, placed on each axle between the driving wheels. An ingenious contrivance was intro B H Fig. 62. duced into this engine. The machine was made to rest upon steam springs. The patentees thus speak of this improvement:-" Our invention consists in sustaining the weight, or a proportion of the weight, of the engine upon FIXED AND LOCOMOTIVE ENGINES. 149 pistons, moveable within cylinders, into which the steam or water of the boiler is allowed to enter, in order to press upon such pistons; and which pistons are, by the intervention of certain levers and connecting-rods, or by any other effective contrivance, made to bear upon the axles of the wheels of the carriage, upon which the engine rests." These cylinders are represented in the fig. at H H; they are screwed by flanges to one side of the boiler, into which they project a few inches; they are open above where they communicate with the steam or water in the boiler; they are also open below, where they are fastened upon the frame of the engine. Solid pistons II are fitted steam-tight to the cylinders; the piston-rods are directed downward, and fastened over the axles of the wheels, upon a moveable part of the frame. By this contrivance, the engine is entirely supported by the steam, which forms a spring of the nicest elasticity. Ingenious as this invention is, it is of little practical utility; for, when the steam loses the requisite elasticity for supporting the engine, the pistons are forced upwards into the cylinders, and the steam suspension is destroyed. Modifications of the engine, now described, were adopted: the endless chain was laid aside, and the axles of the driving wheels were cranked by means of a horizontal connecting-rod, a plan which will be more fully described hereafter; but, in the most improved state of the engine, as employed until the year 1829, its maximum performance was to convey forty tons at the rate of six miles per hour; the evaporating power of the boiler being equal to about fifteen gallons of water per hour. 110. Fixed and Locomotive Engines.—In the spring of the year 1829, the Liverpool and Manchester Railway being far advanced towards completion, the directors appointed Messrs. Walker and Rastrick to institute an inquiry into the comparative merits of fixed and locomotive engines, with reference to expenditure, and the capabilities of the machines. Their report contained the following statement:-" Upon the consideration of the question in every point of view, 150 FIXED AND LOCOMOTIVE ENGINES. taking the two lines of road as now forming; and having reference to economy, despatch, safety, and convenience, our opinion is, that if it be resolved to make the Liverpool and Manchester Railway complete at once, so as to accommodate the traffic as stated in your instructions, or a quantity approaching to it, the stationary reciprocating system is the best." Notwithstanding this report, a majority of the directors appeared to be in favour of locomotive engines, provided they could be made of sufficient power, of less weight than those hitherto employed, and capable of consuming their own smoke. A second inquiry was instituted by Messrs. Stephenson and Locke, and with a different result, founded on the increased power gained in the construction of locomotive engines subsequently to the date of the previous inquiry. The two estimates are given in detail in Wood's Treatise on Railroads. The comparison of the two kinds of engines, according to the latter estimate, is as follows: Messrs. Stephenson and Locke observe:-"That, in considering the long chain of connected power of the stationary engines, given out by so many machines, with the continual crossings of the train from one line to the other, and subject to the government of no fewer than 150 men, whose individual attention is all requisite to preserve the commu |