LOCONEOTIVS.
locomotive, considered as a whole, may be defined as an "engine running on wheels," or it may be treated as a boiler supply ing steam to an engine for driving a propelling mechanism. Ordinarily, the term " engine " is applied, not merely to the cylinders, valves, and valve-operating mechanism, but to the entire machine. The importance of the subject, and the difficulty of separating the engine, or motor proper, from the rest of the machine as an entirety, leads us to devote a separate heading to the subject of locomotives, although this heading forms a part of the matter relating to steam-engines.
Locomotives differ essentially in their running-gear from the locomo biles previously mentioned (p. 274). In modern forms of construction the main portion of this running-gear consists principally of "driving-wheels" which have either a smooth periphery (in which case they act by friction upon the surfaces they touch) or a toothed periphery (in which case they catch into a comparatively soft basis or gear into a rack). The carriage is generally a wheeled vehicle, though sometimes a sled (bl. 104, jig. 3), and the motive machine is always a steam-engine.
According to the nature of the roadway over which they are to run, locomotives are differently constructed, and are distinguished as railway-, street-, field-, and ice-locomotives. Street-, and particularly field-, locomo tives are called " traction engines," and where the arrangement for draw ing attached loads is omitted, and the load consists of persons sitting on the locomotive itself, there are applied to it the terms (formerly in general use for the locomotive) steam-carriage, steam-omnibus, and steam-sled.
The locomotive, long in the minds of inventors an ideal wagon mov ing without driver and horses, has only recently been practically realized, and even yet, except for railroads, for whose use it has been crowned with astonishing success, there has been invented no locomotive likely to sur vive that entirely replaces the tractive power of horses or other animals. The real history of the locomotive begins with the period when iron rail roads were first used. These were a development of the wooden tramways originating in the sixteenth century in Germany for mining, and consist ing of flat wrought-iron straps spiked on wooden rails, these rails being replaced in England, about 1700, by low cast-iron rails, and these again, in 182o, by high rails of wrought iron or steel, or of both combined in one rail. (See Vol. V., p. 171.) The invention of the locomotive is associated with that of the so-called "high-pressure" steam-engine—that is, of a steam-engine which can dis pense with the condenser and can be made comparatively small, being for both reasons especially adapted as a motor for a vehicle. Oliver Evans,
the inventor of the high-pressure steam-engine, was also the inventor of the locomotive. Ilis first locomotive, the " Oruktor Amphibolos," was constructed in 18or, and in 1803 ran through the streets of Philadelphia. (See Vol. V., p. 172.) The development and perfection of this invention, however, which should really be classed with street-locomotiVCS, d id nut take place in America. It was perfected in England, where, independent of Evans, Trevithick and Vivian in 1802 took out a patent for the application of a high-pressure steam-engine to a wagon, and in i80.1 produced the first practical railroad locomotive. This fiist English locomotive was of a crude type, and was soon succeeded by a number of scarcely less imper fect constructions by other inventors. They were mostly used for the comparatively slow transport of pig-iron, coal, and other heavy materials. Their running-gear consisted in part of a spur cog-wheel catching into a toothed central rail, or, instead of the wheel, they had a stake-like appa ratus pressing against the ground. They were provided with complicated vertical beam-engines. In 1815-182o, however, George Stephenson brought out a form of construction which, perfected by his son Robert and greatly improved by other inventors, has since 1828 been practically the model of existing locomotives. By this invention Robert Stephenson gained nearly the same rank among his co-workers in this line that Watt occupies among the inventors of the steam-engine. (See Vol. V., p. 171, el seq.) The successful application of the use of the locomotive was based on the fact that the friction or adhesion of a smooth wheel upon a smooth rail sufficed for propulsion, provided the road was nearly level; and a sat isfactory result can be attained only by complying with these conditions and by arranging the engine horizontally and using a multitubular boiler, which, having more heating surface, is capable of producing a great quan tity of steam in a limited space. Another step was the introduction of the so-called " Stephenson's link-motion," which allows of a quick reversal and a great variation in the degree of expansion. This apparatus, as improved by Allen, is shown in Figure 4 Ca 97). Another important feature was in substituting for the bellows, or similar contrivance orig inally used Tor stirring the fire, the exhaust-nozzle and the blast-pipe.