Intelligence and Miscellaneous Articles. 317 



netic elements of both kinds, we find that the magnetic moment 

 communicated to the cylinder by the force F will be, taking account 

 of the reactions of the two sorts of molecules. 

 M= fc+5+2*? F 

 1 — <?kq 

 after the cessation of the force F, they will retain a moment 



m=q± — / FAv. 

 1— crkq 



This quantity is what is ordinarily called the permanent magnetism. 



The temporary magnetism, which disappears on the cessation of 



the force F, is 



fi=~M-m = 7cFAv. 



It is thus seen that the two coefficients of temporary and per- 

 manent magnetism ordinarily determined are not quantities of the 

 same kind. The quantity q, analogous by the part it plays to 7c, is 

 obtained by dividing the ordinary coefficient of magnetism by 

 (1 + cJcf 

 l — c 2 kq' 



It is evident, and verified without difficulty in a particular case, 

 that the total magnetic moment M is intermediate to those which 

 would be produced by the same force F acting on two cylinders 

 equal to the first, each comprising only one sort of molecules, with 

 the same total density. But it is not the same with the residual 

 moment m, which, for a given value of q, is as much greater as the 

 coefficient Tc of temporary magnetism itself is greater ; and as the 

 coefficient h relative to soft iron is enormous, it is seen that the ad- 

 dition of a certain quantity of soft iron to the hardest steel may 

 augment the residual magnetism of the latter. The employment of 

 armatures of soft iron at the extremities of magnetic bundles, in 

 order to increase their power, comes to the support of our asser- 

 tion. We will also remark that, according to M. Jamin, the varie- 

 ties of steel the richest in carbon and tempered the hardest do not 

 present the greatest residual magnetic moments — which is what 

 should be if the molecules of soft iron in them are very rare, as we 

 must suppose them to be. We reserve to ourselves to return to 

 this subject subsequently, and to develop the results by calcula- 

 tion and experiment. 



The complete theory of the phenomena of breaking, on which we 

 were engaged in a preceding communication, required a rigorous 

 knowledge of the two functions of temporary and permanent mag- 

 netism of steel. Let us consider two bodies, A and B, submitted 

 to one and the same inductive force, but united invariably the one 

 to the other. After the cessation of the inductive force the body 

 A remains under the action of B, and conserves, apart from the re- 

 sidual magnetic moment which would remain to it after its separa- 

 tion from B, a moment (of the same or the contrary direction) pro- 

 duced by the influence of B, and which is permanent only so long 

 as the union between A and B subsists. This magnetic excess might 

 be named the subpermanent magnetic moment. In the experiment 



