H. A. Rowland — Studies on Magnetic Distribution. 



eing nearly proportional 1 

 I shall prit 



In the fii-st place, then, this equation shows that the distribu- 

 tion of magnetism in a very elongated electro-magnet, and 

 indeed of a steel magnet, does not change when pieces of soft 

 iron bars of the same diameter as the magnet are placed against 

 the poles, provided that equal pieces are applied to both ends ; 

 otherwise there is a change. This result would be modified by 

 taking into account the variation of the permeability, &c. 



Let us first consider the case where the rod projects out of 

 the end of the helix, as in Tables V, VI and YII. By giving 

 proper values to the constants we obtain the results given in 

 the last columns of the table. The agreement with observa- 

 tion is in most cases very perfect. We also see the same 

 variation of r that we before noticed in the rest of the curves, 

 and we see that it is in just the direction theory would indicate 

 from the change of //. 



In these tables we come to a very important subject, and 

 one to which I called attention some years back, namely, the 

 change in the distribution when the magnetizing -force varies, and 

 which is due to change of permeability. The following tables 

 and figures show this extremely well, and are from very long 

 rods with a helix a foot long at their center, as in the last 

 three tables. The bar in both these tables was 19 inch in 

 diameter and 5 feet long. The zero-point was at the center of 

 the bar and of the helix. The tables give values of Q'^ for 

 the magnetizing-forces which appear at the head of each col- 

 umn, and which are the tangents of the angles of deflection 

 of the needles of a tangent-galvanometer. Table YIII. only 

 gives the part covered by the helix. Both tables are from tlie 

 mean of both ends of the bar. 





strength of magnrtmrigcm-ent. 







•194. 



•3t8. 



•600. 





L, 











K-I 



i 



9-3 



J 



These experiments show in the most positive manner the 

 effect we are considering, and we are impressed by them with 

 the great complication introduced into magnetic distribution 

 by the variable character of magnetic permeability. 



