BELT.) If two cylinders mounted on parallel shafts are set so far away from each other that their surfaces do not touch, one may be from the other by encircling both with an endless• flat belt of flexible material. The driving power from the motor shaft is transmitted to the driven shaft by means of the friction between the sur face of the belt and that of the two pulleys. Change of speed is accomplished by increasing or decreasing the diameter of the driven pulley as compared with the driving pulley. Change in the direction of rotation is accomplished by twisting the belt; thus a horizontal or an oblique pulley can be driven from a vertical pulley. Belt trans mission is particularly an American development and is more extensively used in this country than elsewhere. in English practice for many years gearing was preferred to belts, and at present rope drivers are used in England in preference to belts. Rope transmission is similar to belt transmission in principle and operation, but in place of flat belts, embracing smooth-faced pulleys, one or more parallel endless ropes are used, embracing groove-faced pulleys. Rope transmission, like belt transmission and transmission by gearing, involves the use of shafting as a part of the trans mission system. See SHAFTING.
The dynamic or wire rope transmission is a special development of rope transmission, whose most familiar example is perhaps the cable rail way. The dynamic transmission is especially suited to distances up to about one mile. Water under high pressure (700 to 2000 pounds per square inch and upward) affords a very satisfac tory method of transmitting power to a distance, especially for the movement of heavy loads at small velocities, as by cranes and elevators. The system usually consists of one or more pumps ca pable of developing the required pressure (see PUMPS AND PUMPING M AC II INERY ) ; one or more accumulators by which a quantity of water may be accumulated at the required pressure (see ACCUMULATORS) ; the distributing pipes, and the presses. cranes, or other machinery operated. See 11 YDRA ULIC PRESS: HYDRAULIC PRESsURF, ENGINE.) Systems of hydraulic transmission for general industrial purposes exist in London, Liv erpool. Hull, Birmingham. and Manchester, Eng land; in Antwerp, in Holland; in Zurich, and in Geneva, Switzerland : and in many other places.
Air under pressure is one of the most e,xten sively employed means of power transmission at present practiced. Some of the great variety of uses to which compressed air is put at present are listed in the article on AIR COMPRESSORS. The system for compressed air transmission usually consists of an air compressor plant. including re ceivers, for compressing air and storing it under compression (see AIR COMPRESSORS) , the pipes for conveying and distributing the compressed air, and the drills, hoists, and other motors oper ated. (See DRILLS ; PNEUMATIC TOOLS ; HAM MERS ; AIR BRAKE; COM PRESSED-AIR LOCO Mo 11 YE : DISPATCH.) The longest dis tance to which air has ever been transmitted in America is three miles, at the Chapin mine, Iron Mountain, Michigan.
The most modern and in some respects the most important means of power transmission is electricity, which is now used for lighting. street railway, and general purposes, in constantly in creasing amounts. The system for electric power transmission consists of the generating plant of engines and dynamos (see DYNA MO-ELECTRIC MACHINERY ) . the transmission line wires, cables or bars, and the motors operated. (See ELECTRIC RAILWAYS; ELECTRIC LIGHTING; STORAGE BAT TERIES; TRANSFORMERS.) One of the earliest at tempts at long distance electric transmission was made between Munich and Meisbach, Germany, in 18S2. The distance was 32 miles. In 1886 power was transmitted between Creil and Paris. France, 36 miles, and in 1891, on the occasion of the elec tric exhibition at Frankfort, Germany, power was transmitted from to Frankfort, 109 miles. The longest transmission line in America is from Redlands to Los Angeles, Cal.. SO miles. There is also a 24-mile line from Folsom to Sacramento, Cal., and a 35-mile line at Provo, Utah.
BIBLIOGRAPHY. For the best available literaBibliography. For the best available litera- ture on power transmission, see Kent, Mechanical Engineers' Pocket Book (New York. 1900) ; blather, Rope Driving (New York, 1895) ; Mark, Hydraulic Power Engineering (New York, 1900) ; Richards, Compressed dir (New York, 1895) ; Unwin. Development and Transmission of Power (London, 1894).