386 Mr. P. W. Burbidge on the Absorption of the 



than silver rays. From the relation 



r/p = A.\ x 



(where r/p is the mass ionization absorption, \ is the wave- 

 length, A is a constant for a particular material, and x is a 

 universal constant, approx. 3), then 



T 1 /P,=A 1 X 3 , T/^ApV 3 



r 2 /p 2 = A 2 X 3 , T 2 'jp 2 = A 2 \' 3 



whence t 1 /t 2 = t 1 7t 2 ', 



as Barkla and Collier * found. 



Hence the correction can be made for the different wave- 

 lengths, since r ± for the gas is measured with the rays used, 

 t 2 for aluminium is also measured (6'14), and t 2 ' for alumi- 

 nium for silver K rays (6*62) is known. 



The corrected values are tabulated : — 



Gas. 



Press. 

 Eange 



(mm. Hg). 



observed. 



V- 



(corr. for 

 scattering). 



(j"-'2p). 



r 



(corr. for 



Rays). 



\i corr. 



(r + -2p). 



P- 



r/p. 

 •35 



nip. 



Air :.. 



1450 



•00059 



•00068 



•00042 



•00045 



•00071 



•00129 



•55 



00 2 ... 



1450 



■00091 



•00105 



•00065 



•00076 



•00110 



•00198 



•35 



•55 



so 2 ... 



1440 



•0069 



•0072 



•00662 



•00715 



•00773 



•00288 



2-50 



270 



CH 3 I. 



130 



•0905 



•1060 



•1047 



•114 



•1153 



•00638 



17-9 



18-1 





In fig. 3 are shown the present experimental results together 

 with those of Barkla and Collier (loc. cit.) and of E. A. Owen |, 

 the graph representing the variation of log r/p with log \. 



The figures given by Owen in bis paper are for total 

 absorption, as he used a narrow beam ; those of Barkla and 

 Collier are given as total absorption, but since probably they 

 used a fairly wide beam there would be some correction 

 necessary. However, for this purpose the value of the mass 

 scattering coefficient, *2, has been subtracted from both sets 

 of values., Siegbahn J has plotted similarly some of Barkla 



* Barkla and Collier, Phil. Mag. June 1912. 

 t E. A. Owen, Proc. Roy. Soc. lxxxvi. A, 1912. 

 X Siegbahn. Phys. Zeitschr. 1914 ; Siegbahn gives these values, by 

 mistake, as Owen's. 



