LOCOMOTIVE ENGINE. Any en gine which, being employed to draw loads in transport overland, travels with the load which it draws.
Since the improvement and extension of iron railways, this term has been ex clusively applied to the steam engine, by which loads are drawn upon them. Al though, strictly speaking, the steam en gine by which a ship is propelled is a lo comotive engine, it is not usual to apply that term to it ; such an engine is called a marine engine. (See STEAM NAVIGA no:sr.) The term locomotive engine must, therefore as at present used, be under stood to mean the travelling steam engine by which trains are drawn on railways.
History of the Locomotive Engine.— The first practical application of the steam engine as a locomotive power took place in 1804, on a railroad at Merthyr Tydvil, in South Wales. The engine was constructed by Messrs. Trevethick and Vivian, under a patent obtained by them two years previously. This engine, in several respects, resembled in its form and structure those which have been since used for a like purpose.
The boiler was a cylinder, with flat cir cular ends placed upon its side. A large tube entered it at one ene end, and, being carried near the other, was there received and carried back parallel to its first direc tion ; its course through the boiler resem bling the letter U. 1'he two months or openings of this tube were therefore placed at the same end of the boiler. One of the mouths of this tube communicated with the chimney, the base of which was flanged upon it, and the other contained the grate and furnace. The flame and heated air were drawn through the curved tube, and up the chimney. The engine was worked by high-pressure steam without condensation ; the steam being admitted to the cylinder, and withdrawn from it, by the well-known mechanical contri vance called a four-way cock. The cyl inder was placed on its side ; and in one position of the cock a communication was opened between the boiler and one end of the cylinder, while another com munication was opened between the other end of a cylinder and a tube lead ing to the chimney. Steam was thus ad mitted to act on one side of the piston, end allowed to escape from the other side to the chimney. When the piston attained the end of the stroke the posi tion of the cock was reversed, and the steam which had just driven the piston in one direction was allowed to escape to the chimney, while steam from the boiler was admitted on the other side of the piston, to impel it in the contrary direction ; and in this manner the piston was continually driven backwards and forwards, in a horizontal direction, and parallel to the direction of the load. The
piston rod was moved through a hole cor responding with it in magnitude, in the cover of the cylinder, in which it was ren dered steam tight by a stuffing box proper ly lubricated. The piston rod acted by means of a connecting rod oria crank,which it kept in revolution in the same manner as the crank in a common double-acting steam engine is moved. (See STEAM EN GINE.) On the axle of this crank was placed a cogged wheel which by means of ordinary gearing, conveyed motion to the axle of the hind wheels of the engine, so as to keep that axle in constant revolu tion. The wheels being keyed upon that axle, so as not to be capable, like the wheels of a common carriage, of turning upon it were necessarily made to revolve with it ; and so long as their pressure upon the road was sufficient to prevent them from slipping, a progressive mo tion of the carriage was the necessary consequence of their revolution.
The early projectors of locomotive en.. gines were all impressed with a notion that the adhesion of the driving wheels with the rails must be insufficient to en able the power applied to these wheels to give progressive motion to the carriage ; and, withou, thinking it necessary to as certain by actual experiment, whether such were really the case or not, they ex pended much ingenuity and capital in de vising means of overcoming this difficul ty, which, after all turned out to be merely imaginary. Engineers were, in fact, impressed with a notion that if any power compelled the wheels to revolve, they would merely slip upon the rails, and that the carriage or engine would re main stationary. To provide against this, Messrs. Trevethick and Vivian proposed to make the external rims of the wheels intended for common roads rough and uneven, by surrounding them with pro jecting heads of nails or bolts, or by cut ting traverse grooves in them. Seven years afterwards, Mr. Blinkensop, of Leeds, obtained a patent for a method of surmounting this imaginary difficulty by the substitution of a rack rail for the ordi nary smooth rail, and constructing teeth to the driving wheels to work in the teeth , in this track Various other ingenious contrivances were subsequently produced for the same purpose, until about the year 1814, when experience at length forced upon engineers the knowledge of the fact, that the adhesion of the tires of the wheels with the rails was amply sufficient to propel the engine, even when drawing after it a great load.