MOLECULAR ENERGY 297 



Petit noticed the fact that the product of the specific 

 heat per gram and the atomic weight was approxi- 

 mately 6.4 calories. They announced the fact as an 

 empirical law, years before the idea of an equiparti- 

 tion had been developed. 



More recent measurements have shown that this 

 relationship is the accidental result of the temperatures 

 of their experiments, for as the temperature is decreased 

 the specific heat is found to have lower values, approach- 

 ing zero at the absolute temperature of zero. Thus 

 C v for carbon (from measurements on a diamond) is 

 5.51 at 1258 absolute; 5.29 at 880; 3.63 at 520; 

 2.12 at 358 ; 1.35 at 283 (10 C.) ; 0.76 at 222, 

 and practically zero at 50 absolute. 



As a solid is heated, its changes in temperature are 

 manifested to our senses by the radiation of heat, and 

 later by luminous radiations, first dull red, but finally 

 all those of the spectrum, hi which condition the solid 

 is incandescent. According to the modern theory, this 

 light is due to the oscillations of the electrons. These 

 electronic oscillators we should expect to be displaced 

 from their equilibrium positions by collisions or by 

 interactions with the electrons of atoms in their im- 

 mediate neighborhood. According, however, to the 

 theory advanced by Planck, they will be caused to oscil- 

 late only by the receipt of a definite amount of energy, 

 a quantum. The quantum is not necessarily the same 

 for two different oscillators, but depends upon their 

 natural ! frequencies, being d = hf, where / is the fre- 

 quency and h is known as " Planck's constant. " 



1 The natural frequency of a system is the frequency at which it 

 will oscillate if displaced from its equilibrium, and then left free 



