GAS AND OIL ENGINES 



time the engine had no great commercial utility. The 

 idea was revived, however, about three-quarters of a 

 century later and an engine operated on Cayley's 

 principle was commercially introduced in England by 

 Mr. Buckett. This engine has a cold-air cylinder above 

 the crank-shaft and a large hot-air cylinder below, while 

 the furnace is on one side enclosed in an air-tight 

 chamber. The fuel is supplied as required through a 

 valve and distributing cone arranged above the furnace 

 and provided with an air lock in which the fuel is 

 stored. At about the time when this hot-air engine was 

 introduced, however, gas and oil engines of another and 

 more important type were developed, as we shall see 

 in a moment. 



Meantime, an interesting effort to utilize the expan- 

 sive property of heated air was made by Dr. Stirling in 

 1826 ; his engine being one in which heat was distributed 

 by means of a displacer which moved the mass of air 

 to and fro between the hot and cold portions of the ap- 

 paratus. He also compressed the air before heating it, 

 thus making a distinct advance in the economy and com- 

 pactness of the engine. From an engineering stand- 

 point his design has further interest in that it was a 

 practical attempt to construct an engine working on the 

 principle of the theoretically perfect heat engine, in 

 which the cycle of operations is closed, the same mass of 

 air being used throughout. In the theoretically perfect 

 heat engine, it may be added, the cycle of operations may 

 be reversed, there being no loss of energy involved; but 

 in practice, of course, an engine cannot be con- 

 structed to meet this ideal condition, as there is neces- 



