( 107 ) 



the current streiigtli amounted to 7 amperes; the RöntgEiN bulb was 

 "soft". 



Sometimes I obtained one maximum only or an irregular action 

 on the film, but this was only the case with an asymmetric position 

 of the apparatus. 



From these experiments we may deduce: 1^^ that the primary 

 RöNTGEN rays are polarised at the utmost only to a very slight 

 amount, and 2"^ that possibly an asymmetry in the arrangement 

 caused the maxima and minima observed in the experiments of 

 Barkla, who did not observe at the same time in two diametrical 

 opposite directions. 



With nearly the same arrangement I repeated Barkla's experiments 

 on the polarisation of secondary rays, wdiich he has shown also by 

 means of electroscopes and described Proc. Roy. Soc. Series A vol. 

 77, p. 247, 1906. 



S 



G. 



5: 



A. 



R 



4 



U 



n 



JL 



n 



p 



'F 



Fi^."^ 



u 



Let the arrow (fig. 2) indicate the direction of incidence of the 

 RöNTGEN rays on the carbon plate K large 8 X ^ cm. and thick 

 12 mm. The secondary rays emitted by this plate could pass through 

 the brass tube G, which was fastened to S^. This tube was 6 cm. 

 long and on the frontside it was provided with a brass plate with 

 an aperture of 5 mm. It was placed within the leaden case at 8 cm. 

 distance from the middle of the carbon plate; leaden screens protected 

 the tube against the direct action of the primary rays. In these 

 experiments the above mentioned induction-coil was used with a 



