38 Dr. G. D. Cooksey on Asymmetry in the Distribution 



summary of which is to be found in the Phil. Mag. for 

 Sept. 1911, page 396, has afforded a convenient mean- of 

 obtaining homogeneous beams of X-rays of known pene- 

 trating powers over a wide range. Tt was by this means 

 that the experiments described in the present paper were 

 performed. 



Apparatus and Method. 

 The apparatus used is shown in the accompanying diagram 

 and was a modified form of the apparatus used in previous 

 experiments *. 



Y 



ToElcctrosccke £z 



T 



T 



I 



ie Ei 



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

 • »o\, and the rays, proceeding from the anti-cathode, K. 

 passed through a window in the box and Pell on the radiator, 

 K], which consisted of a metal known to give off fluoresced 

 X-rays. The fluoresced raya Erom K, passed through 

 windows in a lead screen, S, into the ionization-chambers, 

 A and l», which were maintained at potentials of +240 and 

 — 210 volts respectively. A wire. ( \ passing into A and \\ 

 through insulating plugs was connected to the gold leaf of a 

 sensitive electroscope, K,, of the type described by \\. T. 

 Beatty f. The two quadrants of this electroscope were 



* Am. Jour. Sri. vol \\i\. p. 386 i L907), 



t ri.il. Mag. vol, xiv. p. 001 (1907). 



