Dr. C. Fromme on the Magnetism of Steel Bars. 199 



the experiments now to be described a correction was never 

 necessary. 



The distance from the compass to the scale amounted to 

 1350*58, that of the magnetometer from the scale 1303*96 of 

 the scale-divisionsV 



The magnetizing helix, in all these experiments, which had 

 the special purpose above stated, stood at the same distance of 

 200*11 millims. from the magnetometer. The constant dis- 

 tance was necessary on account of the minute quantities to 

 be measured, and the small distance because the deflection of 

 the magnetometer was otherwise too insignificant. 



Here, however, when I was not satisfied with comparative 

 measurements of the residual moments expressed in scale-divi- 

 sions, but wished also to make observations of the temporary 

 moments, and to apply them to quantitative measurements for 

 the calculation of the magnetization-function, the difficulty 

 arose that the distances of the poles of the ellipsoids entered 

 into the reckoning with, in part, a very great relative value 

 to the distance 200*11 millims. 



Now Eiecke *, from the theoretical point of view, has deve- 

 loped an expression for the polar distance of uniformly mag- 

 netized bodies ; and he found it particularly simple in the case 

 of the magnet having the form of a solid of rotation. 



If we assume that the fifth power of the half-length of the 

 magnet may be neglected against the fifth power of the dis- 

 tance of the point affected, then the polar distance of an elon- 

 : gated ellipsoid of rotation whose rotation-axis a coincides with 

 its magnetic axis, if b denotes the minor axis, is 



A trial of this formula by studying the deflections of the 

 galvanometer-needle with different distances of the ellipsoid 

 (which possessed a certain amount of permanent magnetism), 

 showed a fair accordance of the magnetic moments calculated 

 from it with the aid of the polar-distance formula. Hence 

 Biecke's formula was afterwards always made use of without 

 ; hesitation. 



The ellipsoid was always inserted in the helix or taken out 

 of it with a closed current, in order to exclude as much as 

 possible the production of induction-currents. 



Table III. (pp. 200, 201) gives the temporary moments TM, 

 ; the current-intensity i, the external magnetizing force X, and 

 ; (as far as if was possible to calculate them) the magnetization- 

 \ function k and its argument K ; also, expressed in scale-divi- 



* Ndchr. vond. Gessllsch. d: Wissensch. w G6ttingen y 1872, No. 12 • Pogg\ 

 Ann. vol. cxlix. 



