Deflexion of cc Rays from Radium and Polonium. 



.39 



of scintillations 

 but the amount 

 one to make a 



this method of observing the position of the end of the beam 

 of a rays. 1 learned later that Mr. F. H. Glew of London 

 has used this arrangement in his " scintilloscope/' and he 

 kindly consented to make for me the excellent zinc-sulphide 

 screens used throughout these experiments. 



It was hoped that the position of the line 

 could be observed by means of a microscope, 

 of light was found to be too faint to enable 

 setting with a cross-hair. The method adopted was to put 

 the film side of a photographic plate in contact with the glass 

 side of the zinc-sulphide screen, and photograph the scintil- 

 lations. In order not to increase the width of the line unduly, 

 the thickness of the glass of the screen had to be as small as 

 was consistent with strength to withstand the atmospheric 

 pressure inwards when a vacuum was made in the vessel. 

 The thickness used was from three to four fifths of a millimetre 

 according to the size of the opening to be covered by the 

 screen. 



Magnetic Deflexion of a. Rays from Radium. 

 The design of the tube finally adopted for the measure- 



ment of the deflexion of the a rays 

 magnetic field is shown by figure 1. 



Fisr. l. 



from radium by a 

 The vacuum-box is 



made of brass, and consists of a solid disk A at one end, a 

 hollow cylinder D at the other, and a tube BC joining them. 

 The shape of the latter is shown by the small drawings [ci) 

 and (b) in the figure, its dimension parallel to the length of 

 either slit being the same, 9 mm., at all parts to enable the 



