160 OF THE POWER OF STEAM, [SECT. iv. 



form for the piston, would cause more friction, and expose a larger portion of 

 surface to the cooling effect of the atmosphere. These are radical objections to 

 the rotary action of steam that cannot be removed by art. 



318. It is so obvious, that it is not necessary to show, that the impulse of 

 steam cannot be employed without great loss of fuel ; we may, however, take a 

 general view of the modes in which the action of steam may be applied. 



MODES OF APPLYING THE POWER OF STEAM. 



319. The arrangement being presented in a tabular form, will be more clear 

 than in continued description. The modes of obtaining the different species of 

 power, and the measures of their effects, have already been explained ; for conden- 

 sation, in art. 291. ; for generation, in art. 295. ; and for expansion, in art. 297. 



f 1. the generation of steam. (Worcester.) 

 320. The action of steam as a moving force is I 



< 2. the expansion of steam. (Hornblower. 

 derived from - 



I 3. the condensation of steam. (Savery.) 



Of the species of action there may be used 



The action may be J * 



L by impulse. 



f generation, 

 separately ( 



. condensation. 



1 and 2. 



1 and 3. (Savery.) 

 t 2 and 3. (Hornblower.) 

 [_ 1, 2, and 3. (Woolf.) 



a solid, (Newcomen,) ) f continuous. 



successive. 



_,, . f a solid, (JNewcomen,) i ( 



The action may be exerted on ( aflu . d> (Worcester>) } and may be { 



The motion of the surface acted upon may be in a ( strai ht 1 j; ne 



I curved / 



321. The pressure of steam is the kind of action which is employed in prac- 

 tice ; and the reasons for giving the preference to rectilineal motion have been 

 shown, art. 317. In order that it may be economically employed, it is found 

 that a solid is best adapted to receive its action, fluids being liable to decompose 

 by contact with hot steam, or to condense and waste the steam. And, in con- 

 sequence of a cylinder being the figure adapted to the object, and possessing the 

 greatest capacity with the least surface, and therefore having the least loss both 

 by cooling and by friction, it is almost universally employed. The action is 



