296 THE REALITIES OF MODERN SCIENCE 



The more thoroughly one is accustomed to the scien- 

 tific formulation of the laws of matter and energy 

 which hold for visible masses, the more impossible 

 seems such a phenomenon as has been suggested. We 

 expect that a system will absorb energy in any amount 

 and increase continuously in its energy, and we cannot 

 as yet visualize a molecular mechanism of the sort we 

 have implied above. 



In the case of solids the principle of equipartition is 

 even farther from representing the facts. The mole- 

 cule of a solid cannot leave its boundaries and must 

 have all its energy in oscillation about a mean position. 

 As it departs from that position it forms with adjacent 

 molecules systems of increasing potential energy. As 

 it returns toward the mean position this potential 

 energy is converted into kinetic energy. Heating the 

 solid increases the kinetic energy of the " oscillators," 

 as we might call them. The average potential energy, 

 however, increases equally with the kinetic. There 

 are three mutually perpendicular axes along which 

 the molecule may vibrate and there will be required 

 one calorie of p.e. and one of k. e. for each of these 

 three degrees of vibrational freedom. We should 

 therefore expect a total of 6 calories. 



The molecular heat of monatomic solids, that is, the 

 atomic heat of elementary substances, is in many 

 instances about 6 calories, as is evident from the follow- 

 ing values: carbon 5.5, boron 5.5, sodium 6.7, magne- 

 sium 5.9, phosphorus 6.2, sulphur 5.9, silver 6.0, 

 copper 5.9, iron 6.4, nickel 6.3, aluminium 5.9, zinc 

 6.1, platinum 6.2, gold 6.2, cobalt 6.0. In the early 

 days of calorimetric measurements (1818) Dulong and 



