420 



M?' Beatty, The production of Cathode Particles 



is evidence in favour of both of them, and they are the simplest 

 that can be made. 



Now if / be the amount of ionisation in air due to the cathode 

 particles which emerge from the leaf, and X the coefficient of 

 absorption of these particles in silver, then a simple integration 

 shows that \I is the amount of ionisation which would be caused 

 if all the cathode particles set free in unit thickness of the silver 

 were able to spend their whole energy in ionising air instead of 

 being absorbed by the leaf 



Since for any set of cathode particles the absorption in air is 

 proportional to the absorption in any other substance*, we may 

 use the former value instead of the latter, if we are not compelled 

 to use absolute values. 



Hence if we multiply the numbers in Table I, column 3, by 

 the corresponding values of A, in column 2, we get numbers giving 

 the amounts of cathode energy liberated by different kinds of 

 X- radiations when they are equally absorbed in silver. The results 

 are given in column 4. 



These numbers are seen to be of the same order of magnitude 

 though the numbers in column 3 vary widely. No closer agree- 

 ment is to be expected considering the three assumptions which 

 have been made in getting this result. 



Hence we are justified in concluding that the amount of energy 

 spent by the incident radiation in producing cathode particles is 

 proportional to the energy of that radiation which is absorbed by 

 the leaf. 



The experiments were now repeated, using pure hydrogen 

 instead of air in the chamber A. The results are given in 

 Table II. 



Table II. Hydrogen. 



The first column gives the thickness in cms. of the layer of 

 hydrogen at 760 mm. pressure and 15° C. required to cut down 

 the energy of the cathode particles to half its value. 



* Lenard, Wied. Ann., lvi., 1895, p. 255. 



