INTENSITY OF MAGNETIC AND DIAMAGNETIC FORCES. 721 



keeper, the intensity of the magnetism produced by polar in- 

 duction by no means increases in the same proportion as the 

 intensity of the current. Hence if the object be not to de- 

 termine merely whether the magnetic attraction remains the 

 same, but also to correct the forces which are requisite for the 

 withdrawal of the watch-glass from the halves of the keeper, with 

 regard to slight variations in the intensity of the current, the 

 method of proceeding described in the last paragraph is no longer 

 applicable. We must then substitute for the small pointed iron 

 cylinder a watch-glass filled with some magnetic substance, re- 

 sembling as much as possible that in which the other substances 

 were placed when tested in regard to magnetism ; and whilst in 

 the balance, it must be allowed to be withdrawn from time to time 

 from the two halves of the keeper in exactly the same manner. 

 ITie weights requisite to effect this evidently afford a measure 

 of the intensity of the magnetism in action during the experi- 

 ments in question ; they may evidently be considered as pro- 

 portional to these weights ; and hence when the intensity of the 

 current varies, they may be corrected. 



The necessity of the new method of determination is evident 

 from the weighings detailed below, which Avere made for this 

 purpose. Once under the same conditions as in the previous 

 paragraph, the force which was requisite for withdrawing the 

 small iron cylinder was determined ; and on another occasion, 

 the force, with which a watch-glass containing the fatty mixture 

 III., consisting of 1000 parts of lard to 16 of iron, when applied 

 to the approximated halves of the keeper, was retained by them . 

 When four freshly-filled cells were used in succession to excite 

 the magnetism, the following results were obtained : — 



Number of cells. Attraction of the cylinder. Attraction of the watch-glass, 

 grms. grnis. 



1 100-4 15-46 



2 178-9 34-15 



3 239-6 50-15 



4 294-8 60-40 



12. The supporting power of a magnet is a completely indefi- 

 nite expression, principally because the mass of the keeper sup- 



mventis, applies this method to determine numerically the distribution of the 

 magnetism in the surfaces of the poles of the large electro-magnet, in keepers 

 and in steel bars, to measure the influence of the inducing action of poles of the 

 same and of different names, and, in my opinion, has obtained results which 

 decidedly deserve the preference over those obtainable by other methods, espe- 

 cially those of Coulomb by steel magnets. 



