the Electrical Conduction produced by it. 



129 



rate of leak between A and B for different distances from the 

 base-plate was determined for pressures of 760, 370, and 

 190 mm., and the results are given below : — ■ 





Rate of leak between plates. 



Distance of A 

 from Uranium. 



Air 760 mm. 



Air 370 mm. 



Air 190 mm. 



cl {— 35 mm.) 

 ,, + 2'5 mm. 



„ + 5 „ 

 „ + 7-5 „ 

 „ +10 „ 

 „ +12-5 „ 

 „ +15 „ 



1 



67 

 •45 



•31 

 •21 

 •16 



... 



1 

 •71 



•51 

 •36 



1 



•78 

 •59 



For the purpose of comparison the rate of leak at the 

 distance d is taken as unity in each case. It can readily be 

 deduced from the results that the intensity of the radiation is 

 reduced to half its value after passing through 



4'3 mm. c 



>f air at 760 mm. 



10 „ 



,. 370 „ 



19-5 „ 



„ 190 „ 



The absorption is thus approximately proportional to the 

 pressure for the range that has been tried. It was not 

 found feasible to measure the absorption at lower pressures 

 on account of the large distances through which the radiation 

 must pass to be appreciably absorbed, 



A second method of measuring the absorption of the radia- 

 tion in gases, which depends on the variation of the rate 

 of leak between two plates as the distance between them is 

 varied, is given in § 12. 



§ 10. Effect of Pressure on the Rate of Discharge. 



Becquerel * has given a few results for the effects of 

 pressure, and showed that the rate of leak due to uranium 

 diminished with the pressure. Beattie and S. de Sinolan f also 



* Comptes Rendzis, p. 438 (1897). 

 t Phil. Mag. xliii. p. 418 (1897). 



Phil. Mag, 8. 5. Vol. 47. No. 284. Jan. 1*99. 



K 



