from Thin Metallic Sheets. 



271 



The intensity of the X rays was measured by an ionisation 

 chamber / (with thin aluminium bounding walls), and a Wilson 

 electroscope : the usual insulation and shielding precautions were 

 taken. If the rays were cut down by a screen, it was, of course, 

 inserted between the aluminium window and the ionisation 

 chamber. 



The anticathode was earthed and put in metallic contact with 

 the tube-anode A or A'. The whole of the discharge tube could 

 be slewed round by means of the mercury-trapped ground-joint J, 

 which led also to the pump. Thus the X rays proceeding from 

 either window could be measured by the one ionisation chamber : 

 one had only to rely on the constancy of the discharge. 



Results. 



