4 Art. 8.— Y. Takahaslii : 



During the whole course of the experiment, it was desirable 

 to regulate the length of the spark gap, which was adjustetl by 

 clamping the terminals to the poles provided with an arrangement 

 like a spark micrometer, b}^ which the distance between the 

 sparking terminals was changed so as to obtain a spark best 

 suited for the exferiment. 



Electromagnet. 



The electromagnet used was so constructed that the cores 

 with the coils can be displaced along their common axis ami 

 rotated as a whole about the vertical axis, which enabled us to 

 bring the middle of the magnetic field on the line of collimation 

 of the optical system, keeping this line and the magnetic lines of 

 force at right angle with each other. 



A current of I'o to 23 amperes from the secondary battery 

 was used according to the magnetic field desired, and its 

 constancy was carefully observed by means of a small adjustable 

 resistance and an ammeter by Siemens & Halske. 



Conical pole pieces ending in circular sections were used 

 during the whole course of the experiments, the diameter of the 

 faces and the air gap between them were 2 cm. and 1 cm. 

 respectively for weak fields, and 0*3 cm. and 0'12 cm. for the 

 strongest ones, the diameter and the gap being changed between 

 these limits. 



For the purpose of examining the character of the magnetic 

 separation, it was desirable to extend the range of the magnetic 

 field as wide as possible, but it was difiicult to apply a field 

 stronger than 37230 gauss with tlie electromagnet in our 

 laboratory for the spark gap giving a source of light of consideralde 

 intensity, the diameter of the faces of the pole pieces and the air 

 gap between them being limited as m-entioned above, for further 

 approach of the pole faces caused short-circuit of the sparking 

 current through them, and further diminution of the diameter 



