338 



Mr. C. A. Sadler on 



gators were very inconsistent. This evidently is only to be 

 expected, since the primary beams used in all these investi- 

 gations were necessarily heterogeneous, and it is impossible 

 to determine which constituents of these various beams were 

 chiefly concerned in producing the corpuscular radiation 

 measured in any particular instance. 



While investigating the secondary radiation of the 

 Eontgen type emitted by metals exposed to a primary beam 

 from a Rontgen tube J, it was found that the radiation from 

 each element whose atomic weight lies between those of 

 chromium (52) and tin (119) was quite characteristic of that 

 element, and moreover was very homogeneous. 



The coefficients of absorption in aluminium of these homo- 

 geneous radiations have a wide range of values as will be 

 seen by reference to the following Table. The coefficient X 

 is defined by the equation 



where I is the initial intensity of the radiation and I the 

 intensity after passing through a plate of aluminium of 

 thickness x cm. 



Table I. 



Element from which 



the secondary homogeneous 



radiation is obtained. 



Atomic weight 



of 



element. 



\, the absorption 



coefficient of the 



radiation in 



aluminium t. 



Chromium 



52 



55-9 



59-0 



61-3* 



63-6 



65-4 



75-0 



79-2 



87-6 



960 

 1030 

 1079 

 1190 



367 

 239 

 193-2 

 159-5 

 128-9 

 1063 

 60-7 

 510 

 35-2 

 12-7 

 8-44 

 6-75 

 4-33 



Iron „ 



Cobalt 



Nickel 



Copper , 



Zinc 



Arsenic 



Selenium 



Strontium 



Molybdenum 



Rhodium 



Silver 



Tin 





* Note the atomic weight of nickel is here given as 6P3 instead of the 

 usual value 587, for reasons explained in a paper on the atomic weight of 

 nickel (Barkla and Sadler, Phil. Mag. September 1907, and in later papers). 



t Some of these values are quoted from a paper by Barkla and Sadler, Phil. 

 Mag. May 1909. 



Perhaps it is hardly necessary to point out the enormous 

 + Barkla and Sadler, Phil. Mag. Oct. 1908, pp. 550-584. 



