by Homogeneous Rontgen Radiations. 



419 



certain series of Z-radiations, then the ratio of their coefficients 

 of absorption for this series of X-radiations remains constant for 

 each one of this series. 



Since silver* and airf exhibit no homogeneous radiation when 

 stimulated by the range of radiations here employed, we may 

 assume that their coefficients of absorption have a constant ratio 

 for each X-radiation. 



We shall further assume that the ionisation in air is pro- 

 portional to the coefficient of absorption of air. 



Hence ionisation of air oo absorption by air of radiation 

 absorption by air oo absorption by silver. 



.•. ionisation of air oo absorption by silver. 



£ii9de ioi{iscitto7i 



Vieny^-^Q of dcr 



Fig. 2. 



Hence the ratio (Table I, column 3) is a measure in arbitrary 

 units of the ratio of the energy of cathode particles emerging 

 from the silver leaf to the amount of energy absorbed by the leaf 

 from the X-radiation. 



From the numbers in Table I, column 3, we can attempt to 

 calculate the total energy due to cathode particles produced in 

 the whole volume of the leaf when the leaf absorbs a fixed quantity 

 of radiation. 



Two assumptions must be made : 



(1) That each cathode particle moves initially in the direction 

 of the incident X-radiation. 



(2) That these particles are absorbed according to an ex- 

 ponential law in the silver leaf itself. 



These assumptions have not been definitely proved, but there 



* Ihid* loc cit* 



t Beatt'y, Phil. Mag., Nov. 1907, pp. 604—614. 



