SECT, v.] NONCONDENSING ENGINES. 183 



loss of heat in the operation ; consequently, as far as the generation of the steam is 

 concerned, the lower the force the better. But in the noncondensing engine the 

 steam has to work against the pressure of the atmosphere, and loses so much of its 

 effect ; hence the more its force exceeds the atmospheric pressure, the greater will 

 be the effect of a given quantity of steam in proportion to this loss. On the 

 contrary, when the strength of the steam is considerable, there is much waste by 

 leakage, 1 which with the extra expense of fuel tends to counterbalance the ad- 

 vantage of increasing the force; and considering these circumstances, with the 

 danger of strong steam, it appears to me that steam of four or five atmospheres is 

 about the best force for these engines. 



1 The rate of increase of loss by leakage may be estimated, for it depends jointly on the goodness 

 of the workmanship, and the force tending to separate the parts. Now a good workman may fit 

 the parts so that they would not exceed, under a strain of 1 atmosphere, a continued aperture of 

 the 5000th part of an inch in breadth; and then if/ be the force in inches of mercury, and a the 

 diameter in inches, the magnitude of the joint will be, 



3-1416 a f 3-1416 af 



30 x 5000 = 150000 SqUa 



The velocity of escape will be less than 6-5 V 86-5 (459 + t) or 60 V 459 + t (art. 136.) ; con- 

 sequently, the quantity lost per second cannot exceed, 



3-1416 af y/ 459 + t 

 2500 



If v be the velocity of the piston in feet per second, the steam required in the same time will be 

 7854 a 2 v; hence, the quantity required being unity, the loss will be less than, 



3-1416 af ^459 +1 _ f y/ 459 + t 

 7654 a*v x 2500 625 a t; 



When v = 4, a = 10, /= 133, and t = 300, 



625 a v 



