94 



Prof. E. Bouty's Studies on Magnetism. 



Thirty passages to the spiral did not raise much the magnetic 

 moment of this needle*. The results obtained by the disrup- 

 tive discharges are less regular than the preceding, although the 

 empiric formula still represents them. The irregularities doubt- 

 less proceed from the difficulty of working these discharges in 

 perfectly identical conditions. 



The preceding experiments already establish that the extra 

 currents are without magnetic action within the coil which pro- 

 duces them. If it were otherwise, interruption would be a more 

 efficacious process of magnetization than passing the needle to 

 the spiral ; now augmentation of the magnetic moment has never 

 been observed when needles magnetized by a great number of 

 passages have been submitted to repeated breakings of the 

 circuit. 



II. The circuit comprises, besides the pile, two coils P and Q. 

 The phenomena observed on account of slow passages are the 

 same as in the case of a single coil ; but the effect of the extra 

 currents complicates the phenomena arising from interruption. 

 We will suppose the coil P much more powerful than Q. If the 

 two coils are placed one after the other, two needles/* and q, 

 magnetized, each in the corresponding coil, to the limit relative 

 to the passages, acquire a greater magnetic moment through the 

 interruptions; but the relative increment is much greater in the 

 less powerful coil. Example : — 



Table VI. — Needles 142 millims. long and 2 millims. 

 in diameter. 



Needle^. 



Needle q. 



First passage. 1751 



Second passage 18-21 



Twentieth passage .. 18-70 

 21 interruptions ... 1891 



First passage 3 22 



Second passage 3'63 



Twentieth passage ... 415 

 21 interruptions 5*61 



The extreme magnetization corresponding to the passages, 

 from the first two observations of each column, would be, accord- 

 ing to our empirical formula, 18"61 iov p, and 4*04 for q. The 

 increment of the magnetic moment produced by the interrup- 

 tion is, iov p 0*21 in absolute value, and about -fa in relative 

 value ; for the needle q the values are 1*46 and J. 



* The two preceding experiments were made immediately after those of 

 Table I., with needles almost identical and in the interior of the same 

 spiral. The establishments and interruptions are effected by means of a 

 cup containing mercury, into which the extremities of the conducting wires 

 dipped. 



