Mathematical and Physical Papers. 211 



t™n«f *'"' f'f "' ^TT"' "'" P"™" '° '"' depended upon is that 

 transformod from the heat energy stored in the fuels that are avail- 

 able through the agency of some form of heat engine. There are 

 two general classes of these engines. In one the heat of the fnel 

 IS applied to some liquid, usually water, in a separate vessel, or 

 bmler, and the vapor thus formed is led to the working cylinder of 

 the engine, where it gives up its heat to produce the energy of 

 moving machine parts. The steam-engine with its boiler is the 

 only practical example of this class. It may use any fuel, as coal 

 oi , or gas, that wi 1 supply the heat. I„ the other cLs the fuel t 



of air and there burned. The heat so generated is applied directly 



flnW OfT'^'i ' "\f' ^"'' ""^ •'""^•^ 8»^«^ '°™« the working 

 finid. Of this class the most prominent types are the gas-engine 

 theoil-engme (using crude petroleum directly), the gasoline-engine 

 tit engiuTr"'""^""'' '^'''^ "'■' designated as internal-combus- 

 The fuel used by the gas-engine may be natural gas, artificial gas 

 from the producer used for general gas production' or that from a 

 special form of suction-gas producer, in which the engine in draw- 

 ing in Its fresh charge of air and gas furnishes the draught necel 

 sary to maintain combustion in the producer. This last system is 

 becoming popular, due to its economy in operation and L com 

 pactness and unity of the plant. Several electric generating planl 

 using this system have been installed in this state during^he la t 

 few years, and more are in process of erection. The fuel used in 

 the producers now in operation is anthracite coal, but at least one 

 company IS now perfecting plans for a producer adapted to the use 

 of he b tummous coal mined in this section of the country This 

 system IS of the greatest importance, since it insures theperma 

 nence of the gas-engine so long as the coal supply holds out 

 Natural gas is good where it may be had and as long as it lasts but 

 t can hardly be considered as a permanent fuel, and could not be 

 accepted as fulfilling the condition for an abundant source of power 



i he oil-engine, using crude petroleum directly as a fuel has been] 

 brought out in the United States in a really satisfacto y form by 

 only one company. . In this form it is a German design controlled 

 by the Diesel Motor Company, of New York, and buiUbv the 

 American and British Manufacturing Company in ProviLje R 

 I. In operation, the oil is pumped under high pressure into the 

 engine cy inder, in which air has been compressed to a pre sure of 

 500 pounds to the square inch. The oil is forced in ^^Zl 



