Prof. E. Bouty's Studies on Magnetism. 199 



distance may be transformed into attraction at a very short dis- 

 tance, in consequence of the temporary magnetism developed by 

 induction. This fact was observed in the last century by Mus- 

 schenbroek and (Epinus. 



The phenomena connected with temporary magnetization play 

 a great part in all questions relative to the breaking of magnets. 

 Let us consider generally two bodies, A and B, submitted to the 

 action of one and the same inductive force, but constantly united 

 to one another. After the cessation of the inductive force the body 

 A remains under the action of B, and retains, apart from the resi- 

 dual magnetic moment which it would retain after the removal 

 of B, a moment produced by influence, which is compounded 

 with the former, and which is permanent only so long as the 

 union of A and B subsists. It might be named the subperma- 

 nent moment. The same reasoning applies if A and B are 

 two portions of one and the same body ; and it is evident that 

 to determine the permanent moment taken by a body under 

 the action of an inductive force is an eminently complex pro- 

 blem, and one that can only be solved generally by knowing 

 the laws of temporary as well as permanent magnetism pro- 

 perly so called. We commend this consequence to the atten- 

 tion of investigators of the theory of magnetism. 



In the experiment of the bundle broken parallel to the axis 

 the subpermanent is opposite in direction to the permanent 

 magnetism. On the contrary, the two are identical in direction 

 in the case of a needle broken in a plane perpendicular to its 

 axis, and of which the fragments are separated or reunited end 

 to end. The moment of the fragments brought into contact is 

 greater than the sum of the moments of the separated fragments, 

 and yet falls short of the value of the moment of the entire 

 needle before it was broken. This is readily verified by ex- 

 periment. 



IV. On the Theory of Steel Magnets. 



The physical theory of magnetism exists almost entirely under 

 the form of comparisons. As in nature there cannot be two 

 series of phenomena absolutely parallel, unfortunately those 

 comparisons only awaken in the mind ideas which are imperfect 

 and never entirely satisfy it. Even Ampere's beautiful theory 

 of molecular solenoids is, perhaps, not wholly unaffected by this 

 remark, which applies especially to the coercive-force theory, as 

 well as to all other attempts which have been made for the pur- 

 pose of elucidating the theory of steel magnets. 



It was Coulomb who first established with some precision the 

 difference between iron and steel in regard to magnetization, 

 and introduced the notion of coercive force. He compares the 



