OF STEAM ENGINES. 



165 



the great consumption of fuel ; a considerable portion of the 

 caloric employed in the generation of the steam being absorbed 

 in heating the new surface of cold water last raised from the well ; 

 and where great heights are required, there appears no mode of 

 completely obviating this objection. Should it, however, be requir- 

 ed merely to raise water about thirty feet, there are few contrivan- 

 ces more economical or better adapted for general use. While 

 speaking of Savery's apparatus, it may be advisable to notice 

 the very ingenious adoption of the same principle to the con- 

 struction of a gas-engine by Mr. Brown. In the latter case a 

 vacuum is formed by the introduction of an inflamed jet of car- 

 buretted hydrogen gas, which consumes the oxygen, and rarefies 

 the nitrogen by the increase of temperature which ensues. The 

 vacuum thus produced is much more perfect than would at first 

 view have been supposed from the nature of the process resorted 

 to by the patentee, but the economy of employing hydrogen gas, as 

 a substitute for condensible vapour, is still somewhat problematic. 

 The atmospheric engine will come next in order, and its claim 

 to practical utility is much greater 

 than either of those we have yet de- 

 scribed. The cylinder b is in this 

 case placed over a boiler , and if we 

 suppose the piston be made to fit air- 

 tight, it will be evident that it must be 

 driven up by the action of the steam 

 beneath, should a sufficient supply of 

 heat be applied ; when this is effected, 

 the condensible vapour may be re- 

 duced to its original bulk by the in- 

 troduction of water from the cistern i. 

 In the working engine however, the ascent of the piston is effect- 

 ed by the action of the lever e g acting on the fulcrum /; to the 

 end g of this lever or working beam is attached the pump rod h, 

 and it will be apparent that whenever that preponderates over 

 the piston p, the latter must be drawn up. On the readmission 

 of the steam, a new supply of condensing water is introduced by 

 turning the cock /, and the pressure of the atmosphere above the 

 piston being unbalanced by any resistance beneath, the end e 

 is again depressed, and the pump rod again elevated. The pipe 

 g is employed to carry off" the condensing water which would 

 otherwise accumulate within the cylinder ; and the small forcing 

 pump with its rod v s supplies the condensing cistern t by the 

 pipe t. 



LECT. 



V. 



