192 Dr. C. Fromme on the Magnetism of Steel Bars, 



where e is the constant of induction, w the resistance of the 

 circuit, F the surface enclosed by the coils of the helix, X the 

 inducing component ; and 



J = 8tt-S.M, 



S being a constant determined by the dimensions of the helix 

 and ellipsoid, and M the magnetic moment of the ellipsoid in 

 the direction of its principal axis. 



By inserting these values of J and i in the first equation, 

 we get 



M=G.X, 



1 . a . 



4^ >sin 2" sm 2 F 



IS s' 



G=. 



sm 2 



Neumann's formula, 



k.v. 



1 + kC 9 



in which v is the volume of the ellipsoid, and C the previously 

 mentioned constant dependent on the eccentricity, serves for 

 the calculation of the magnetization-function k : 



, G 



K ~ v + GC 



In conclusion, the argument is 



X 



K= 



1 + &C 



§ 4. The inductor consisted of a brass tube 547 millims. 

 long, and 43'5 in diameter, on which four layers of insulated 

 copper wire were wound ; the surface enclosed by the wind- 

 ings was 



F = 1735000 squ. millims. 



The values of the quantity S for the five ellipsoids lie between 

 1*4537 and 1*4533. The amount of the components of the 

 earth's magnetic force is taken from Kohlrausch's variation- 

 formula*, according to which they are found to be, for the 

 middle of February 1874, 



V=4*314, 



H= 1*866. 



* Nachrichten von der Gesellsch. d. Wissemch. zu Gbtt. 1868, p 159. 



