246 



PROCEEDINGS OF Till; AMERICAN ACADEMY. 



in which the / mb La the magnetization as determined magnetometri- 

 caily, and the I. „* is found Gran the B as determined ballistically 

 ut the centre of the roil in the nana] way. For this rod m = 300. 

 The abscissae represent //', the magnetic field applied from without. 



Similar curves had also been previously published by Dr. L. Holhoru.- 1 

 only the SQSceptibilities were taken directly from the unsheared m 

 cetization curve of a short cylinder. 



Although these experiments of Holborn and Benedicks practically 

 prove the increased uniformity of magnetization for low field-, it u 

 perhaps a better plan to settle this poinl by a more direct method. It 

 was therefore thought that it might be of interest to compare the 



10 20 30 40 50 60 70 e0 90 100 110 120 130 WO 150 160 170 ',00 B0 200 



FlGURK 21. 



Benedicks's curves, showing variation of the pole-distance ratio and the B I 

 tihility in an iron rod. The abscissae give the field II' in c. g. s. units. 



actual magnetic induction which passes through various cross-sections 

 of some of our iron rods, for practically the whole range of magnetiza- 

 tion from zero to saturation. To do this one might use a secondary 

 search-coil, fitting loosely around the 'iron rod, which can be suddenly 

 displaced along the rod by any desired distance. This would require 

 two observers; but it could not be used conveniently in thi< work 

 since the rods in which the magnetic induction was tested were !.'.»< •■"» 

 cms. in diameter, and the inner diameter of the brass tube around 

 which the solenoid coils were wound was not much larger. Another 

 method would be to wind ooils around different parts of the rod and 

 L r ft the actual induction passing through each coil. This would do 



21 Sitzber. Akad. .1. Wias., Berlin, 1. 169-162 L8 - 



