Rontgen Radiation and Corpuscular Radiatic 



451 



iron and copper radiators respectively. The amount of 

 tertiary radiation excited by the radiation from either copper 

 or iron in E 2 was negligible, since the vessel was lined with 

 aluminium. In the ionization-chamber I, however, copper 

 radiation readily excited tertiary radiation in the iron, while 

 the radiation from iron excited little or none. The ratio 

 when iron was used as secondary radiator will give us a 

 measure of the ratio which would be obtained with copper 

 as secondary radiator if no tertiary radiation were excited in 

 the iron. The actual ratio when copper is used as secondary 

 gives a measure of the ionization due to the secondary from 

 copper, together with that due to the tertiary from iron. This 

 latter ratio divided by the former gives the value of R 2 ". 



The mean of several determinations, all of which agreed 

 among themselves very closely, gave 1*045 as the corrected 

 value for R". 



Substituting in equation (10) the value of &/ was found 

 to =2*00. Most of the values of k' and X x and X 2 were 

 taken from a previous paper, a few, however, being specially 

 determined. The method of measuring these absorption 

 coefficients A 2 and X 4 was as follows. A stout brass cylin- 

 drical vessel A, 20 cm. long, in the centre of each end of 

 which was drilled a hole 1*0 cm. diameter, which was after- 

 wards covered with thin aluminium ('003 em.), was placed with 

 its axis along the line joining the centre of the radiator E 2 to the 

 centre of the w indow of the electroscope E 2 , as shown in fig. 2. 



Fig. 2. 



■15 CM- > 



CM 



\li 



IQCM- 



The pressure of the air in A was reduced by connecting it 

 to a water pump, the pressure being indicated by a mercury 



