98 THE NATURE AND [SECT. n. 



its specific heat, allowing for the exposed side of the cylinder decreasing, is equal 

 to that of 



200 ( / + d) d v 



16 



cubic feet of steam heated one degree ; but the temperature will rise to the mean 

 between the condensing and boiling points, or to 



160 + 212 _ 18fi o 

 2~ 



or the addition of heat will be 26 degrees. The whole quantity of heat consumed 

 will therefore be 



200 x 26 (/ + d)dv 



This divided by the capacity of the cylinder, or - , gives 



16 



- 



50 x 26 (/ + d) 

 Id ~~> 



the loss it would sustain in temperature, or 



1300 (/ + rf) 



^ -- > * an d d being here both expressed m feet. 



When the length of the cylinder is twice its diameter, or 2 d = I, the loss becomes 



1950 



d 



Now one-fifth of the whole power is lost by imperfect condensation, more 

 than in engines with a separate condenser ; which is equal to 



-i 197 



iigi- = 225 degrees of heat ; 



and by the condensation and cooling in the cylinder, we have found 



1950 



d ' 



Hence the total heat, over and above what is required in other engines, is equi- 

 valent to converting into steam 



1500 



times the water necessary for the steam engine, with a condenser and steam 

 pressure. 



With a cylinder 1*5 feet diameter, double the fuel is required, but for a 6-feet 

 cylinder only one-third more than in the single engine of Watt's construction. 



164. This enables us to illustrate the fact observed by Mr. Watt, when he 



