Mr Richardson, 'On an attempt to detect radiation, etc. 171 



joined to b by thin pressure tubing, and they were clamped inde- 

 pendently so that by keeping b fixed and raising the clamp of A, 



PUMP ete 



H 



Leaden 

 Ja.r. 



^eycLen. Jar 



/ s 



Fig. I. 



the wire was lifted out of the mercury cup and a spark gap 

 produced. The apparatus was made light-tight with black paint, 

 except for a small space near C which was generally covered with 

 black paper held in place by a rubber-band. This enabled the 

 spark gap to be observed when desired, and the quality of the 

 discharge to be ascertained. The tube i was placed vertically in 

 the gap between the pole pieces of an electromagnet, which were 

 close up against it. The width of the air gap was thus equal to 



