330 Production of Cathode Particles by Rontgen Radiations. 



distance between radiator and ionization vessel was increased 

 by six cms., bnt only a change of one per cent, was obtained 

 in X when Sn was used as radiator. An attempt was made 

 to use a parallel beam of radiation by causing it to pass along 

 the axes of a bundle of lead tubes placed between radiator 

 and vessel, but the effect then became too small to measure. 



It should be mentioned that the portions of the screws 

 between - R and E (fig. 2) were covered with paper sheaths 

 to prevent the emission of any particles from them. 



An experiment was also made in which a circular disk of 

 lead was placed immediately under the parchment window 

 (fig. 2) with a central hole, 2 centimetres in diameter, cut 

 out of the lead. 



The Sn radiation was limited by this hole so that none of 

 it fell on the screws or on the cylindrical portions of the 

 vessel. The value thus found for A, was 3*89, nearly the same 

 as before. 



Experiments are at present being made to find directly the 

 amount of corpuscular energy produced in a substance when 

 a definite quantity of Rontgen radiation is absorbed by it. 

 The results of these experiments can be applied to the re- 

 determination of most of the numbers given in this paper by 

 an entirely different method. The author hopes to clear up 

 in this way the differences already mentioned. 



Summary. 



(1) The absorptions by hydrogen and air of cathode 

 particles excited by homogeneous Rontgen radiations have 

 been measured. 



(2) It has been deduced from the numbers obtained that 

 the amount of corpuscular energy set free in silver is roughly 

 proportional to the energy of the exciting radiation absorbed 

 by the silver. 



(3) The relation between the absorption of the cathode 

 particles by air and the absorption of the exciting homo- 

 geneous radiations by aluminium is nearly linear. 



(4) The direct ionization in hydrogen relative to that in air 

 has been measured when homogeneous radiations of different 

 penetrating powers were used to cause the ionization. 



(5) When a given set of cathode particles spends all its 

 energy in producing ions in air or in hydrogen the total 

 number of ions produced is the same in each gas. 



(6) The penetrating power of the cathode particles has 

 been found to be the same whether emitted from the emergent 

 or incident side of the leaf. 



I wish to thank Professor Sir J. J. Thomson for his interest 

 in these experiments. 



