182 OF THE CONSTRUCTION OF [SECT. v. 



which, corrected, becomes when x = I, 



385fal 1 1 + hyp. log. m n \ -385 m n af I. 

 Or 



385/ a 1 1 1 + hyp. log. mn- mnf ' \ = the power. 



383. The ratio of the capacity of the large cylinder to the small one is 

 dependent on the amount of friction and loss of force. In the small cylinder the 

 loss must be the same as in the cylinder of an engine working at full pressure ; this 

 appears from our mode of inquiry to be 0'4 of the force of the steam in the boiler, 

 (art. 367.) And in the second cylinder the friction of the piston, the cooling of 

 the cylinder, and the excess of force required to expel the steam into the atmo- 

 sphere added together make '016 + -2 + '007 = '223 of the remaining force, or 

 223 x '6 + '4 = -5338 = the whole loss in the two cylinders. Hence, 



5338 / + 30:/:: 1 : m = .5333 y + 3 Q = the capacity of the large cylinder, when 



that of the small one is unity. 

 If/= 120 inches, then, 



5338 f + 30 = 1'28, the relative capacity of the large cylinder. 



And in all cases the value of m n must be less than that of n in the note to 

 art. 377. Also, since -533S/ + 30 =/', we have, from art. 382. 



385/a* (l + hyp. log. m n - ^') = -385 /' v hyp. log. . 



3Q . 



for the power of the engine, of which the velocity of the small piston is v feet per 

 minute, and its diameter a inches, the whole force of the steam being / inches of 

 mercury in the boiler. 



Consequently, the power is less in an engine with a double cylinder, than in one 

 with a single cylinder, in the ratio of, 



the hyperbolic log. of ^SBS to that of T- 



A decrease of power and a more complex arrangement renders the double 

 cylinder engine inferior in every respect, except that of the moving force being 

 more equable than in a single cylinder. 



384. Of the best force for the steam of noncondensing engines. The circum- 

 stances determining the choice of the force of the steam are almost entirely of a 

 practical nature. As far as regards the production of the steam itself, a greater 

 quantity of fuel will be required to generate strong steam, and there will be more 



