
MECHANICAL ACTION OF HEAT. 193 
pressure is equal to that of liquid water x 0-305. Its dynamical value is 
therefore 
1 
Kp =k + GnM~ 1389 6 x 0:305 
=422:83 feet=129-18 metres per centigr. degree. 
1 
But Gnu 153:48 feet= 46-78 metres per centigr. degree. 
Therefore the real specific heat is 
k =269'35 feet= 82:40 metres per centigr. degree. 
Or, that of liquid water being taken as unity, 
kK 269-35 
K, ise96 °° 
The ratio of these two values of the specific heat of steam is 
1+ N=157. 
Their dynamical equivalents for FAHRENHEIT’S scale are 
k = 149-64 feet . . . K, = 235-46 feet. 
Neither the formule in the fourth Section, respecting the working of the 
steam-engine, nor the tables at the end of the paper, require any alteration; for 
the action of steam at full pressure being calculated from data independent of 
its specific heat, is not at all affected by the discrepancy I have mentioned; and 
the expansive action is not affected to an extent appreciable in practice. 

