724 PLUCKER ON THE DETERMINATION OF THE 



from the electro-magnet, and which we shall call the normal 

 attraction, would amount respectively to 



2795-68 grms. 1114-25 grms. ; 



consequently the disturbing effect of induction is respectively 



— 608-18 grms. —118-25 grms. 



If we consider the normal attraction as equal to unity, this 

 amounts relatively to 



0-186 0-089. 



15. In the example given in paragraph 13, the disturbing action 

 of induction increases the normal attraction ; in the example 

 contained in the previous paragraph, it diminishes it. If in the 

 latter instance Me had withdrawn the cup from the surface of 

 one of the poles instead of from the two portions of the keeper, 

 we should, on the other hand, have obtained a disturbing effect of 

 induction, which would have increased the normal attraction. 

 Experiment evidently confirms this ; I shall not, however, detail 

 any numbers, because the exact estimation of the weight is at- 

 tended with some difficulty arising from disturbing influences. 



If we imagine two iron bars to be placed one upon the other 

 on the same pole, in consequence of the original action of the 

 electro-magnet, poles of different names become excited at the 

 place of contact, and mutually strengthen each other. But if two 

 rods, forming a bridge from one pole to the other, are superim- 

 posed, the poles of the same name are excited at the corre- 

 sponding ends, in consequence of the original action ; and these 

 poles become weakened by their mutual action. Thus, while in 

 the first instance the disturbing action of induction necessarily 

 augments the magnetism excited in the iron, in the second case 

 it must weaken it. 



In this way the whole appears to be perfectly explicable*. 



§ 2. Comparison of the Intensity of the Magnetism of different 

 substances. 



16. The method of determination used consists, as stated in 

 the preceding paragraphs, in placing different magnetic substances 

 in the same space in a watch-glass closed by a cover ; then, the 



* Hence it is very probable, that in the experiments with the lard, detailed 

 in paragraph 9, the difference occurring in the first fatty mixture really arises 

 in part from the disturbing action of induction. 



