Prof. E. Bouty's Studies on Magnetism. 205 



porary magnetism ; and the quantity which plays the same part 

 in the expression of m, 



j]+ck){l+dk) 

 9 \-cdkq ' 



is called the coefficient of permanent magnetism. 



The quantity really comparable to the coefficient A is, from 

 the foregoing, the coefficient g*. 



It is evident, and without difficulty verified in a particular 

 case, that the total magnetic moment M lies between those 

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

 cylinders equal to the first, each of which comprised only one 

 species of molecules, with the same total density. But the 

 same is not true of the residual moment m, which for a given 

 value of q is greater in proportion as the coefficient of temporary 

 magnetism of the soft iron is itself greater ; and as this last co- 

 efficient is enormous, it is evident that the addition of a certain 

 quantity of soft iron to the hardest steel can augment the resi- 

 dual moment of the latter. 



It will be recollected that, according to M. Jamin, the varie- 

 ties of steel which are the richest in carbon and of the hardest 

 temper do not exhibit the most powerful residual moments ; 

 and it should be so if the molecules of soft iron in them are very 

 rare, as we must suppose them to be. 



Recapitulation. 



We have indicated a new method for comparing the magnetic 

 moments of very small magnetized needles. 



We have investigated the effect produced upon a magnet by 

 repeatedly passing it to the spiral, by interruption or reestablish- 

 ment of the inducing current, &c, and have given empiric for- 

 mulae fitted to represent the results obtained. 



We have studied the effects of the breaking and division of 

 cylindrical and prismatic magnets, either perpendicularly or 

 parallel to the axis, and verified by experiment, in the case 

 of needles of small diameter, an important formula given by 

 Green to represent the magnetic moment of saturated needles 

 of various lengths and different diameters. 



Lastly, on the ground of the peculiar facts examined in this 

 memoir, as well as the whole of the known facts, we have shown 



* If the coefficients c and d be supposed equal, the formulae will be a 

 little simplified (see Comptes Rendus de VAcad. des Sciences, Feb. 23, 

 1874). Only a complete theory could explicitly state the values of the 

 four coefficients Jc, q, c, and d as functions of the densities d and 8 1 of the 

 two kinds of elements, and consequently establish relations between 

 these four quantities. 



