G. D. CooJcsey — Secondary Cathode Rays. 



49 



Apparatus and Method. 



The apparatus used is shown in the accompanying diagram 

 and was a modified form of the apparatus used in previous 

 experiments.* 



The X-ray tube was completely enclosed in a thick lead box, 

 and the rays, proceeding from the anti-cathode, K, passed 

 through a window in the box and fell on the radiator, R„ 



:]k 



To Elcctvoseofie £z 



~ ~A I 



^ flectroteofie f 2 



which consisted of a metal known to give off fluorescent 

 X-rays. The fluorescent rays from R, passed through windows 

 in a lead screen, S, into the ionization chambers, A and B, 

 which were maintained at potentials of 4- 240 and — 240 volts 

 respectively. A wire, C, passing into A and B through insu- 

 lating plugs was connected to the gold leaf of a sensitive elec- 

 troscope, E„ of the type described by R. T. Beatty.f The 

 two quadrants of this electroscope were connected to A and B 

 respectively, and the wire, C, was normally connected to earth. 

 A third ionization chamber, D, received some of the rays 

 from R, and was always connected to earth. A wire 

 running from the inside of D and insulated from it con- 

 nected with the gold leaf of a second electroscope, E a , of 



* This Journal, vol. xxiv, p. 285, 1907. 

 fPhil. Mag., vol. xiv, p. 604, 1907. 



Am. Jour. Sci.— Fourth Series, Vol. XXXIV, No. 199.— July, 1912. 

 4 



