Production of Fluorescent Rontgen Radiation. 369 



It is now possible to calculate as completely as the expe- 

 riment demands what should be the difference in the effici- 

 encies of the two radiators I. and II., supposing that the 

 bombardment theory to be an accurate representation of: fact. 



From Whiddington's* results, assuming the general law, 

 velocity of ejection of corpuscles by tin radiation 



= 119 xlO 8 



sec 



Now velocity of corpuscles when they no longer have the 

 power of producing gold X-rays I —in Al = 21*6 1 



= 74xlO e 



P 



v8cm. 

 sec* 



Therefore the minimum fraction of energy which they 

 must lose before they cease to produce gold X-rays is 



(119) 2 -(71) 2 ri , 



-~ A ld y = 61 P er Cent ' 



But it is experimentally found that they lose only 30 per 

 cent, of their energy before they emerge from the gold ; 

 that is, they must still possess the power of producing an 

 intense X-radiation from the gold. The experiment shows, 

 however, that the X-radiation is just as intense when this 

 corpuscular energy is absorbed in paper as when it is absorbed 

 in gold. 



If the X-radiation produced in gold be taken as proportional 

 to the diminution in energy of the corpuscles in the gold, the 

 ratio of the X-ray efficiencies of the two radiators would be 



Efficiency of radiator II. _ 9 .-. 

 Efficiency of radiator I. 



Correcting for the surface effect in radiator II., this ratio 

 works out at 



Efficiency of radiator II. _-i.q 



Efficiency of radiator I. 



The experimental ratio of the two efficiencies is 



Efficiency of radiator II. _.qq 

 Efficiency of radiator I. 



No conceivable hypothesis as to the relative efficiencies of 

 corpuscles of varying velocities in producing X-rays can 

 explain this difference between the theoretical and the expe- 

 rimental ratio. So that this experiment seems clearly to 



* Proe. Boy. Soc. A. lxxxvi. p. 376 (1912). 



