of MM. P. Carle and C Cheneveau. 



363 



From (15) 



K- 



/ 



k -A' 





T'/ " 



Iv 

 K' 



= K'A +r -''K'A 



K 

 K 7 



= >' 



r * / 1 



L 1+ K'VaT.-2 



?•- 



D + D" m! 

 D' + D" ' m ' 



(Hi) 



iii which 



When the comparison body is water 



K' exactly = -0'79xlO- 6 (P. Curie). 



As for air the susceptibility « // =0*0322 x 10 - *. 

 If r is positive we have for a paramagnetic body 



K 



p = -r[l + 0^1^+1); 



and for a diamagnetic body 



K 

 K' 



= ,[1-0-041 Q-l)] 



Hence the apparatus lends itself very readily to relative 

 determinations, and if we take water as the standard bcdy 

 (K' = - 0*79 X 10~ 6 ) it enables us to obtain an absolute 

 value of the coefficient of specific magnetization of a body. 



But the comparison substance may be a liquid or solid 

 other than water, and such that its coefficient of magnet- 

 ization is of the same order of magnitude as that to be 

 determined. A choice can be made from the tables of 

 magnetic constants. It is convenient if the masses of the 

 bodies compared correspond to the same volume ; on this 

 account the tube containing the substance is always filled to 

 a given mark. When the substances tested are very strongly 

 magnetic, a smaller length may be employed, but in that 

 case it is absolutely necessary that the comparison substance 

 should have the same length. 



The apparatus could be made still more sensitive with the 

 aid of an electromagnet. On the other hand, with a torsion 

 ware of larger diameter, the magnetic properties of iron or 



2 B 2 



