Mean Intensity of Magnetization of Soft Iron Bars. 451 



"with emery paper, except in the experiment represented in 

 the curve at PL IV. fig. 2. 



The mean intensity of magnetization was obtained by 

 dividing the magnetic moment of the bar by its volume ; the 

 calculation being as follows : — 

 Let 21 = length of the bar. 

 d — diameter of the bar. 

 r = distance of the bar's centre from the centre of the 



magnetometer-needle. 

 H = the intensity of the horizontal component of the 

 earth's magnetic field (assumed to be '152 C.G.S. 

 unit). 



= deflection of magnetometer. 



1 =the mean intensity of magnetization. 



_ Htanfl(r 2 -/ 2 ) 2 

 lircFr 



Tan 6 -was obtained from the observed scale-readings (which 

 are proportional to tan 2 6) by expansion. In the experiment 

 VI., owing to the increased length of the bar, a new solenoid 

 which extended 2"5 centim. beyond the bar toward either way 

 was employed, the constant being 23 C.G.S. units of magnetic 

 field per ampere. This solenoid was placed vertically due 

 west of the magnetometer, the upper end of the iron wire 

 being slightly above the level of the magnetometer. The 

 calculation for the mean intensity in this case was 



t Htanflr' 



where r is the distance of the upper end of the wire from the 

 magnetometer *. 



The results thus arrived at are graphically represented in 

 figs. 7 to 14 (Pis. IV., V.) 



Prof. J. A. Ewing has carried this experiment! from 

 length/diameter = 300 to 50 ; the 300 one being found to 

 give practically the same results as those obtained with ring- 

 magnets, and the present results might be looked upon as its 

 continuation, had it not been for the difference in the methods 

 employed. Prof. Ewing's method was a ballistic one ; con- 

 sequently it gives the magnetization in the neighbourhood 



* This experiment VI. is not strictly comparable with the other five, 

 not only on account of the difference in the methods employed, but also 

 on account of the difference in the specimen of iron used. 



t Phil. Trans. 18*3, Part U. 



