364 
ON THE THERMAL EFFECTS OF FLUIDS IN MOTION. 
have hitherto been made on the specific heat of air at constant pressure. The theo- 
retical results, according to this expression and to the determination 1390 for J, are 
as follow for several particular cases : — 
Mean specific heat of 
Mean specific heat of 
Range of temperature. 
air at atmospheric 
air at five times the 
pressure. 
atmospheric pressure. 
Cent, degrees. 
0 to 100 
*2390 
•2428 
0 to 300 
•2384 
•2396 
The comparison of these results with sufficiently accurate direct experiments on 
the specific heat of air at the atmospheric pressure, might lead to a correction on the 
value 1390 found for J by direct experiments on the generation of heat by friction; 
but it must depend on the evidence afforded by accounts of the experimental details, 
whether the value of the mechanical equivalent of the thermal unit is to be corrected 
from them, or whether we may assume the preceding results as nearer the truth than 
the results which they indicate. No such evidence, nor any demonstrating whether 
or not the influence of change of pressure is such as shown in the preceding Tables, 
has as yet been published. 
