318 



Mr Aston, Distribution of intensity 



consider these two extreme types and their explanation before 

 going on to describe the conditions under which they may be 

 attained or approached. In the diagrams the fields of electric and 

 magnetic forces are horizontal and such that positive ions will be 

 deflected to the right and up, negative ones to the left and down. 

 Brightness is roughly indicated by the width of the parabolic patch 

 drawn. 



O 



Fig. 1. Atomic Type. 



Atomic type of discharge. 



Fig. 1 illustrates the first or 'Atomic' type in which apparently 

 the whole of the discharge is carried up to the face of the cathode 

 by ions of atomic mass. Those which pass through the fields 

 without collision produce the true primary streak on parabola 

 m=l, the head of which corresponds in energy to that obtained 

 by the charge e falling through the full potential of the discharge. 

 Now the pressure in the canal ray tube is never negligible being on 

 the average at least half that in the discharge tube, and the 

 ionisation along its length very intense so that in passing through 

 it a large number will collide with electrons, atoms or molecules. 

 The collision and capture of a single negative electron will result 



