M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. 373 
would conduce to the determination of several other important elements 
of the theory of heat, with regard to which we know nothing, or have 
arrived by our experiments at very insufficient approximations only. 
In this number may be included the heat disengaged by the compression 
of solid or liquid bodies; the theory that we have enunciated enables 
us to determine it numerically for all the values of the temperature for 
which the function C is known in a manner sufficiently exact, that is to 
say, from ¢ = 0 to ¢ = 224°. 
We have seen that the heat disengaged by the augmentation of 
pressure dp is equal to the dilatation by the heat of the body subjected 
to experiment, multiplied by C. With regard to the air taken at zero, 
the quantity of heat disengaged may be directly deduced from the ex- 
periments upon sound in the following manner. 
M. Dulong has shown that a compression of 5-= a raises the tempera- 
ture of a volume of air taken at zero by 0°-421. Now the 0°267 unity 
of heat necessary to elevate a kilogramme of air taken at zero under a 
constant pressure by 1°, are equal to the heat necessary to maintain the 
temperature of the gas dilated by of its volume at zero, above the 
heat necessary to elevate the dilated volume, maintained) constant, by 
; ? 1 
‘Ri lt 
1°; the last is equal to O41 
to the first multiplied by 1 + —— 0-491 , ak ; the former therefore, that is the 
= necessary to maintain the temperature of 1 kil. of air, dilated by 
of the first; their sum is therefore equal 
= 
0:07911. 
_ We arrive at, the same results by the application of the formula 
Q=R (B—C log p); 
—. of its volume, at zero, is equal to (0°267) : ( aaa wa)? or to 
whence 
ZQ=RC = 
putting C = aw and observing that a diminution of volume of — o 
1 
corresponds to an increase of pressure equal to 267 of an atmosphere. 
Knowing the quantity of heat disengaged from gases by compression, 
to ascertain that which a similar pressure would disengage from any 
substance whatever, from iron for example, we write the proportion: 
_ 0:07911 of heat disengaged by a volume of air equal to 0°77. of a cubic 
metre, subjected to an increase of pressure equal to of an. ate 
