of Rontgen Rays in Transmission through Matter. 661 



radiation entered the two electroscopes by precisely similar 

 holes. A guide was placed at S, so that absorbers could be 

 placed and replaced in exactly the same position as required. 



Between the bulb and the pump a tube containing charcoal 

 was connected, and by surrounding this with liquid air the 

 exhaustion was facilitated. When the liquid air had been in 

 position for some time, the bulb reached a steady state. 



The nature of the radiation from the bulb was then tested 

 by placing sheets of different substances at S, and the amount 

 by which the rays were absorbed could be deduced from the 

 readings of the two electroscopes. 



When the radiation was cut down by sheets of aluminium 

 and the absorbability of the remainder tested by a thin sheet 

 of aluminium (-00305), the beam appeared very heterogeneous 

 as shown by the following table : — 



Table I. 



Previous per cent, absorption 

 by Aluminium sheets. 



Subsequent per cent, absorption 

 by Aluminium test-piece. 







34-3 



37-4 



26-9 



56-5 



234 



75-5 



17-8 



806 



12-9 



90 



104 



When, however, the beam was cut down by sheets of copper 

 and the remainder still tested with the same aluminium sheet, 

 it now appeared fairly homogeneous, as shown in Table II. 



Table II. 



Previous per cent, absorption 

 by Copper sheets. 



Subsequent per cent.absorption 

 by Aluminium test-piece. 







310 



48-3 



31-7 



73 



30-0 



S3 



301 



In general, it was found that when the beam was cut down 

 by a substance which, under the stimulus of a suitable Rontgen 

 radiation, emits a characteristic homogeneous radiation con- 

 siderably in excess of that which it scatters, e.g. Ni, Fe, &c, 



