1905.] Polarised Rontgen Radiation. 475 



angles ; consequently in a beam of X-rays proceeding in a direction 

 perpendicular to that of the kathode stream there should be greater 

 electric intensity parallel to the stream than in a direction at right 

 angles. 



Such a beam was therefore used as the primary radiation, and the 

 intensity of secondary radiation proceeding in a direction perpendicular 

 to that of propagation of the primary beam from a radiator placed in 

 that beam, was studied by means of electroscopes. 



In the final form of apparatus the intensity of secondary radiation 

 was measured in two directions perpendicular to that of propagation of 

 the primary radiation and to each other, while the intensity of the 

 primary beam was measured by a third electroscope. 



Using paper, aluminium, or air as the radiator, as the bulb was 

 turned round the axis of the primary beam studied, the intensity of a 

 secondary beam was found to reach a maximum when the direction of 

 the kathode stream was perpendicular to that of propagation of the 

 secondary beam, and a minimum when these two were parallel, one 

 electroscope recording a maximum rate of deflexion when the other 

 recorded a minimum. Many experiments were made which proved the 

 evidence of partial polarisation conclusive. 



When heavier metals, such as copper, tin, and lead, which emit a 

 secondary radiation differing considerably in character from the primary 

 producing it, were used as radiators, no variation in intensity of 

 secondary radiation was observed as the bulb was rotated. 



This result was not found to be affected by a considerable variation 

 in the penetrating power of the primary radiation. 



Experiments were made with several X-ray tubes. 



