128 Prof. E. Rutherford on Uranium Radiation and 



Gas. 



Value of X. 





'43 

 1-6 



2-3 

 •93 





Carbonic acid 



Coal-gas 





or, to express the same results in a different way, the 

 intensity of the radiation from an infinite plane of uranium 

 is reduced by absorption to half its value after having passed 

 through 



3 mm. of carbonic acid, 



4' 3 mm. of air ; 



7" 5 mm. of coal-gas, 

 16'3 mm. of hydrogen. 



We see that the absorption is least in hydrogen and greatest 

 in carbonic acid, and follows the same order as the density of 

 the gases. 



The values given above are for the <x radiation. The fi 

 radiation is not nearly so rapidly absorbed as the a, but, on 

 account of the small electrical leakage produced in its passage 

 through the gas, it was not found feasible to measure the 

 absorption in air or other gases ; 



The absorption of the a radiation by gases is very much 

 greater than the absorption of rays from an ordinary Crookes' 

 tube. In a previous paper * it has been shown that the value 

 of X for the radiation from the particular bulb used was "01. 

 The absorption coefficient for the u radiation is 1'6, or 160 

 times as creat. The absorption of the radiation in gases is 

 probably of the same order as the absorption for ordinary 

 #-rays. 



§ 9. Variation of Absorption with Pressure. 



The absorption of the a radiation increases with increase 

 of pressure and very approximately varies directly as the 

 pressure. 



The same apparatus was used as in fig. 3, and the vessel 

 was kept connected to an air-pump. The variation of the 



* Phil. Mag, April 1897. 



