W. A. Norton on Molecular Physics. 217 
of liquids, like water, whose ultimate molecules are compound, 
a portion of the heat propagated should be consumed in expand- 
] 
Capacity of Bodies for Heat,—The fundamental law discovered 
by Dulong and Petit, that the specific heats of elementary sub- 
or atomic weights,—or, in other words, that the atoms of such 
off again and interchanged with surrounding bodies having the 
shows that the heat emitted from a hot body is composed of rays 
of an infinite variety of rates of vibration, between certain limits, 
The physical cause of this fact will appear if we reflect that the 
limits. For the circumstances of equilibrium of these atomettes 
are different, and their rates of vibration when displaced should 
be different. The fact that the most intense heat-rays, in ordi- 
nary cases of combustion, are those of low refrangibility, and 
the phenomena of the evolution of calorific and luminous rays 
When a body is heated to incandescence, indicate that the electrie 
atomettes which are nearest the central atoms have the lowest 
Tate of vibration. : 
_ We have seen that the expansive action of heat is a necessary 
®onsequence of the fundamental principle that the heat-pulses 
Constitute a repulsive force, and that they are absorbed, more or 
Am. Jour. Sct.—Szconp Series, Vou. XXXVIII, No, 113.—Sepr., 1864, 
28 
