Photographic Effect of X-rays and X-ray Spectra. 299 



the difference may be due to absorption o£ energy by the 



parent molecule, — we get for the wave-length of bromine 



•38xl0~ 4 

 X-radiation (series K) the value , n m2 cm., that is 



•59xl0 -8 centimetre about; and of silver X-radiation 

 (series K) *33 x 10 " 8 centimetre. 



If now we plot " wave-length " so obtained and photo- 

 graphic effect for beams producing equal ionizations in an 

 air-electroscope 8 cm. in length, we get a curve as shown in 



fig. i. 



Fio\ 1. 









( 



» 



























s 



































1 



1 









I 



@~ 



N, 























% 









*••■- 







^© 































<3 © 











f 









•33x 



icf 8 c 



tn. 

























«5S> 



10 ~ B c 



m. 





















/ 



V 







Br. 



















Showing* relative photograpliic effects for X-radiations of various 

 " wave-lengths " producing equal ionizations in air (8 cm. 

 thickness). Discontinuous curve shows relative absorptions 

 of these radiations in silver bromide. 



Lower portion of figure shows spectral lines (series K) of 

 Br and Ag. 



It is seen that, commencing with long waves (absorbable 

 radiations), the photographic effect for equal ionizations is 

 practically a constant until the radiation becomes of shorter 

 wave-length (more penetrating) than bromine X-radiation, 

 when the intensity rises. Again, it approaches a constant 

 but higher value until, when the radiation becomes of shorter 

 wave-length (more penetrating) than the radiation charac- 

 teristic of silver, a second increase of photographic effect 

 occurs. The first increase occurs when there is additional 

 absorption of the primary radiation and re-emission of secon- 

 dary radiations from the bromine of silver bromide, the 

 second when the absorption in stiver increases and the energy 

 re-emitted in the form of secondary rays from silver increases 



X2 



