﻿474 Prof. Chattock and Mr. F. B. Fawcett on the 



Richarz*, in which (p. 410) the author suggests rotating ions 

 as the cause of molecular magnetism, and then gives quanti- 

 tative support to his view hy showing that the saturation 

 values of I for magnetic metals are of the same order of 

 magnitude as those calculated from reasonable assumptions 

 as to the period of rotation of the molecules. 



Magnitude of the Effect sought. 



For simplicity of calculation, consider the molecules to have 

 the form of thin rings of diameter 8 ( = 110~ 8 ), rotating about 

 their principal axes, carrying charges q ( = 3x 10 _22 E.M.) 

 and numbering n ( = 10 25 ) to a cubic centimetre of iron. 



Let the magnetic axes of these rings be parallel and similarly 

 directed ; t. e. let the iron be saturated and of magnetic moment 

 I per cub. centim. It is easy to see that if V stands for the 

 linear velocity of any point on a ring along its circumference. 



n 7T8 2 q nhq v ' 



Suppose now that the field by which the molecules are 

 held in position is suddenly increased by an amount H. The 

 number of lines of force which will enter each ring per centim. 



of its circumference is — k • —r- = — r, and the momentum 



7TO 4 4 ' 



imparted thereby to the matter of the ring is consequently 

 — j— q. From this it follow s that if v is the change produced 

 by this process in the original velocity (V) of a ring of mass m, 



m q ... 



V = ~4nf W 



v 

 Now the ratio ^ is the fraction by which the magnetism 



in the iron decreases when H is increased. If we put 

 H= 40,000 (E wing's maximum value about) and 1=1500, 



^? comes out to be 5 x 10 -11 , as stated above. 



From (i.) and (ii.) it is also easy to calculate the loss of 

 heat in the iron due to any increase of H. 



Loss of kinetic energy of the ) ^^-^(V-*)*, 

 nngs m ergs per cnb. centim. / = £ mV „-i W ; 



and since v is negligible compared with Y, the second term 

 * Wied. Ann. lii. p. '385 (1894). 



