340 



Mr. C. A. Sadler on 



[/■ It was desirable that the homogeneous beams used should be 

 of sufficient intensity to produce an easily measured ionization ; 

 for this purpose an arrangement of the apparatus somewhat 

 similar to that employed while investigating the tertiary 

 Rontgen radiation was adopted*. 



Fig. 1. 



zbcnite play. 



The experimental arrangements are shown in plan in fig. 1 

 drawn to scale. 



A rectangular tube of lead 5 cm. long lined with aluminium 

 2 mm. thick, was fitted into the walls of a lead screen which 

 surrounded the Rontgen ray bulb. The rays proceeding 

 from the anticathode K were allowed to fall upon the 

 secondary radiator placed at H lm The secondary rays from 

 Rj entered the aperture A of the ionization-chamber I, 

 passed through the thin aluminium window B 3 and fell 

 upon the tertiary radiator R 2 . This plate was insulated from 

 the ionization-chamber and connected to E 3 , a sensitive 

 electroscope of the type used in the experiments on the 

 tertiary Rontgen radiation. 



A and B were circular apertures in the ends of a tube 

 sliding with a telescopic fit within another tube which formed 

 the outer casing of the ionization-chamber I. This chamber 

 was mounted upon an insulating stand of ebonite. The 

 diameter of the inner tube was 4*8 cm., while the diameters 

 of the apertures A and B were each 2*7 cm. The end B 

 of the inner tube was ground accurately perpendicular to its 

 axis. Thin brass bars in the form of a cross were soldered 



* Sadler, Phil. Mag. July 1909. 



