1118 



Prof. R. Whiddington 



on the three inside faces o£ which the element providing the 

 X-ray electrons was spread in the form of thin metal sheet 

 or powder. 



The upper side of J was a sheet of aluminium thin enough 

 to transmit the X-rays from T with small absorption, but thick 

 enough to absorb completely any direct electrons produced 

 within B *. 



CNLMSCS SCCTION OPT. 



A is the camera chamber, made on the plan adopted by 

 Rutherford and Robinson f in their /3-ray speed measure- 

 ments, so that, with a uniform magnetic field applied at right 

 angles to the plane of the figure, the electrons from J came 

 to a focus on the photographic film F. . 



The slit was *05 cm. in width. 



K is a thick brass partition stretching right across the 

 camera so as to prevent any secondary radiation from the 

 inside oc the camera from reaching F. 



L is a light trap to minimize the effect on F of any stray 

 light from outside or from accidental discharge passing down 

 the glass evacuating tubes. 



G is a collimator for projecting a registration spot of light 

 on F whenever necessary. 



The usual pump and liquid-air charcoal tube method of 

 evacuation was adopted. 



Hie discharge was produced with an ordinary induction 



* This necessary thickness d is calculable from d=v x ja given in Proc. 

 Roy. Soc. (1912). 



t Phil. Mag. vol. xxvi. p. 717 (1913). 



