Prof. E. Bouty's Studies on Magnetism, 97 



had to this consideration, the agreement is satisfactory. On 

 the contrary, hyperbolic formulae are not at all suitable for 

 the representation of experiments of this sort ; they corre- 

 spond to a much slower increase, sensible even after twenty ope- 

 rations of the same kind, while here the augmentation ceases to 

 be appreciable after seven or eight operations. 

 Quetelet represents by a formula of the form 



2/=B(l-0 (3) 



the magnetic moment acquired by a steel bar magnetizea by one, 

 two, . . . x frictions. This formula represents also, as we have 

 just seen, the increment of the magnetic moment produced in a 

 needle by equal induced currents ; it does not suit for that pro- 

 duced by the interruptions of one and the same continuous cur- 

 rent, acting on a needle innocent of all anterior magnetization. 

 A complete theory of magnetism should account for this differ- 

 ence. 



To avoid the intermissions of the principal current in the pre- 

 ceding experiment, the needle should have been placed in a fixed 

 position in its spiral, and its total magnetic moment measured 

 by the method of deviations. The variations observed are related 

 to the permanent magnetism, which may alone be altered by the 

 passage of the induced currents. 



We have seen that the induced currents produced by wresting 

 from contact an electromagnet placed in the circuit produce ab- 

 solutely similar effects. 



V. Effects of piles the current of which is not constant. — If the 

 current of the pile employed is not rigorously constant, the 

 effect of the polarization of the electrodes modifies profoundly 

 the phenomena. The following results were obtained with a 

 pile containing bichromate of potash, prepared several days pre- 

 viously. 



If the circuit comprises, besides the pile, only one coil, into 

 which a needle magnetized by a great number of passages is in- 

 troduced, the establishment of the current augments the mag- 

 netic moment by a quantity more or less considerable, often 

 enormous. The current therefore possesses a much greater inten- 

 sity at the moment of its closing than it retains a moment after- 

 wards. When the resistance of the spiral is augmented, the po- 

 larization is less strong, and consequently the proper effect of the 

 establishment of the current tends to disappear. 



With respect to the interruptions, they have no very marked 

 effect upon the needles, at least while the resistance of the coil 

 is not very strong ; but in the latter case, if we introduce into 

 the coil a strongly magnetized needle with its south pole to the 

 left of the principal current, we always obtain by the interrup- 



Phil. Mag. S. 4. Vol. 49. No. 323. Feb. 1875. H 



