2(34 Dr Barkla, Phenomena of X-Ra>/ Transmission. 



from Cr I - in Al = 13G 1 ; Curve II by the fixiily soft homogeneous 

 radiation from As [ -in Al = 2:2'o j ; Curve III by the fairly pene- 

 trating radiation from Ag ( - in Al = 2*5 1 . 



We thus see from these results that the absorption of a 

 homogeneous radiation by elements of various atomic weights is a 

 periodic function, but iu general an inereasiug fuuction of the 

 atomic weight. Though observations have not been uiade on a 

 suthcieut number of elements to obtain the accurate relation 

 between absorption and atomic weight of the absorbing substance 

 for any one particular homogeneous beam, ditierent portions of 

 similar curves have been obtained from observation of the absorp- 

 tion of other homogeneous beams, aud their shapes reproduced iu 

 the discontinuous cur^'es iu the tigure. 



Ionization. 



An examination of the results obtained by ditierent experi- 

 menters on the ionizations produced in gases by X-rays showed 

 that these phenomena were in all probability also connected with 

 secondary X-ray phenomena, and that the numerous apparent 

 irrecrularities mio-ht be explained in terms of laws similar to those 

 found for absorption. The writer was therefore led to attempt an 

 investigation of the ionizations produced in different gases by 

 homogeneous beams varying considerably in penetrating power. 

 The radiations used were the homogeneous radiations from Fe, Cu, 

 Zu, Br, Sr, Ag, Sn, Sb, varying in absorbability as shown by curve 

 B in tig. 1. * ^ 



The oases and vapours experimented upon were Air, 0, CO.3, 

 SO,, CABv, SnCl,, CH3I. 



The results of preliminary experimeuts may be briefly stated 

 as follows : 



Eange of penetrating power 

 Gas of radiation Eesidts 



O Fe radiation to Ag radiation louization approximately proportional to 



ionization iu air 

 COa ,, ,, „ „ ,, ,, „ 



SO, 

 CoHjBr Fe radiation to Br radiation ,, ,, ,, ,, 



Br radiation to Sn radiation Eelative ionization increased approximately 



tenfold 

 SnCL Fe radiation to Sn radiation Ionization approximately proportional to 



ionization iu air 

 I radiation ... ... ... Eelative ionization considerably greater 



CH3I Fe radiation to Ag radiation louization approximately proportional to 



ionization in air [only slight gradual 

 change, if any] 



