Prof. E. Bouty's Studies on Magnetism, 



91 



in which A— B represents the residual magnetic moment after 

 the first passage. The degree of accuracy of the formula will be 

 seen from the following examples. 



Table I. — Needle 2 millims. in diameter, magnetized by 

 1 Grove's element. 



Number of 



Magnetic 



moment. 





passages to 

 the spiral. 







Difference. 



Observed. 



Calculated. 



1 



51-46 



51-46 



000 



2 



54 55 



54-62 



-0-07 



3 



5543 



55-68 



-0-15 



4 



5610 



56-20 



-010 



5 



55-95 



56-51 



-0-56 



10 



56-48 



5715 



-0-67 



20 



57-68 



5747 



+0-21 



30 



57-92 



57*57 



+0-35 



50 



5775 



57-68 



+007 





A = 57'78, 



B=6-32. 





Table II. — Needle 1*3 millim. in diameter, maguetized by 

 1 Bunsen element. 



Number of 

 passages to 

 the spiral. 



Magnetic moment. 



Difference. 



Observed. 



Calculated. 



1 

 2 



3 



4 



8 



16 



37-50 

 39-37 

 39-99 

 40-47 

 41 09 

 41-52 



37-50 

 39-51 

 40-18 

 40-52 

 4101 

 41-27 



0-00 

 -014 

 -019 

 -0-05 



' +0-08 

 +025 



A =41 -52, B=402. 



The curious augmentation in question has been already ob- 

 served by Hermann and Scholz*. They wrongly confound, in 

 their researches, the effect of a magnetizing spiral and that of a 

 horseshoe magnet, to the poles of which they apply the needle to 

 be magnetized. In the first case, indeed, if the needle is thin 

 enough, it may be regarded as placed in a magnetic field of con- 

 stant intensity, which it certainly is not in the second ; and as it 

 is impossible to place the needle in precisely the same manner in 

 a great number of successive experiments, the law of the increase 

 is masked by a phenomenon of a different kind. These authors 

 * Hermann and Scholz, locis citatis. 



