204 Prof. E. Bouty's Studies on Magnetism. 



manner, let q^Av be the moment corresponding to the elements 

 A, supposing them to be alone. Every molecule of the system 

 B is acted on, not only by the external force, but also by the 

 system A, and vice versd. This reciprocal action, in the same 

 direction as the external force, has the effect of raising the total 

 magnetism above the sum (k + q)YAv. 



If, in order to simplify, we suppose the coefficients k and q 

 independent of F, which will be sensibly true for small values 

 of the inductive forces, the final moment of each of the two sys- 

 tems will be found by a very simple reasoning copied from the 

 elementary theory of electrical condensation*. Designating 

 then by c and d two coefficients depending on the mean group- 

 ing, and also on the density of the elements of the two systems, 

 we find, for the final moment M a of system A, 



M «=* F T^ A <" • ■ W 



and in the same way, 



"r^iSafc*! • (2) 



whence the total moment 



M=M + M 4 =F!±Mi£_+^A„. . . (3) 



If the action of the force F be suppressed, the molecules A 



conserve their magnetism. As to the molecules B, they are 



now under the action of the system A only, which is equal to 



1 4-ck 

 dq¥ -, i » ; they retain a moment 



"'-""nS^ ...... w 



The total residual magnetism is 



-M.^^^^^ 



(5) 



and the magnetism called temporary, which disappears through 

 the cessation of the current, is 



fi = M-m = kYAv (6) 



The coefficient k is what is usually called the coefficient of tern- 



* "We know very well that this theory is not rigorously exact ; but what 

 is required here is merely to get a general idea of the phenomena. Be- 

 sides, we are supported by the example of M. Jamin, who introduced into 

 science the expression "magnetic condensation," in his theory of the 

 effect of contacts of soft iron, 



