INTERNAL COMBUSTION ENGINES) and is usually operated with gasoline as the fuel, although less volatile hydrocarbon fluids, such as benzol, al cohol, kerosene and melted naphthalene may be used conditionally, especially benzol, which is employed regularly in Europe for motor trucks and omnibuses. From these facts it follows that the automobile intended for the transportation of persons and driven by means of gasoline burned in an auto mobile engine is the dominant type. It is to this type that the word automobile is applied without the use of additional qualifying terms. Motor car, car, motor, gasoline car, as well as other terms implying nothing to the contrary, are also usually meant to designate this type only. Gasoline motor trucks and delivery wag ons are variations of it, differing mainly in the dimensions of machine parts and in the ar rangements of the vehicle bodies for the carry ing of loads. Motorcycles (q.v.) would come under the same classification as the dominant type if they had not by common consent, due to their origin and peculiarities as bicycles with a motor equipment, been placed in a separate class. After those mentioned, other varieties of automobiles follow, in point of number of them in use, in this order: Electric trucks and delivery wagons, electric carriages and cabs, steam trucks (mainly in Great Britain), steam carriages.
As at least 95 per cent of all automobiles are operated by means of an internal-combus tion engine, burning a fluid hydrocarbon fuel and probably 90 per cent of these are used for the transportation of persons and constitute the dominant type of automobile, there is good reason for the popular usage in accordance with which the word "automobile,') when used as a noun, refers to this dominant type only. Going a step further in order to avoid all con fusion of terms, the word is used in the following only as an adjective, and the dominant type is designated as a motor car, while trucks and wagons of the same general type (using the same type of engine, especially) are mentioned as motor trucks and motor wag ons, and all other motor vehicles by their more specific names. The division of the very large
subject comes then, so far as mechanical con struction is concerned, under the following heads: (1) Motor cars, (2) Motor wagons, (3) Motor trucks, (4) Electric trucks and wag ons, (5) Electric carriages, (6) Steam trucks and (7) Steam carriages. But not even this division can be strictly adhered to on account of intermediate construction types and the in creasing number of special classes of vehicles in which the purpose and the special equipment adopted for serving it are of greater interest than the automobile mechanism which they share, in the essentials, with many other motor vehicles. Special constructions, among which motor omnibuses (see Mama OMNIBUS), fire department vehicles (see FIRE ENGINE), and army vehicles (see ARMY TRANSPORTATION; AUTOMOBILE IN WAR) are the most important. are treated mainly under special captions. Tractors and motor ploughs, while in part an outgrowth of the automobile movement and industry, are treated quite separately under TRACTORS and MOTOR PLOUGHS.
Every motor vehicle manufactured for the market has so far been made in three structural divisions, (1) the chassis, comprising a frame carrying the whole power equipment, the actu ating and control mechanism, the vehicle springs and axles and the wheels; (2) the vehicle body or carriage work, comprising all parts of the structural unit which is mounted upon the chassis frame for the purpose of carrying the load of persons or goods in a suitable manner, and (3) the accessories, comprising a number of detached or readily detachable devices serv ing secondary purposes. Rubber tires, lamps, speed-recorders, tops, carburetors, lubricators, fenders, motor-starters, air-pumps, lifting jacks — are commonly mentioned as accessories. But tires, electric lamps, lubricators, carburet ors and motor-starters operate in organic con nection with the engine or vehicle mechanism as a whole, and the classification is only one of convenience to indicate that these units are often manufactured separately.