﻿Energy of the Amperian Molecule. 



475 



vanishes. Hence, as mnYv = IH from (i.) and (ii.), it follows 

 that 



Loss of heat in calories ) _IH 

 per cub. centim. . . . / J^' 



(in.) 



where J is Joule's equivalent. For an increase of H of 250 

 at saturation this would mean a fall of temperature of about 

 one hundredth of a degree C. 



This is a well-known expression for magnetic-field energy ; 

 and though obtained in this somewhat roundabout manner, 

 it is of course quite independent of any hypothesis as to the 

 source of the energy being in the motion of the molecules or 

 elsewhere. The above equations simply suggest a mechanical 

 explanation, in the case of magnetic molecules, for the fact 

 that, when energy is put into surrounding space by starting 

 any current A (say the source of H in the above) , it is less 

 when A is alone than it is if a second current B (the mo- 

 lecular current) is already flowing in its neighbourhood ; the 

 difference being wholly derived from the source of B (which, 

 according to the present hypothesis, is the kinetic energy of 

 the molecule) provided B does not change in strength during 

 the process. If it does — in other words, if the second term 

 in the above expression does not vanish — part of the extra 

 field-energy is derived from the source of A, and calculation 

 becomes practically impossible. 



Description of Apparatus. 



After several unsuccessful attempts to obtain reliable values, 

 the arrangement show T n in fig. 1 was adopted. AA are the 



<_> 



F1C.2. 



upper portions of the coils of a large electromagnet. BB are 

 small auxiliary coils for the purpose of producing an alteration 



2K2 



