MASS SPECTRA OF THE ELEMENTS ASTON. 



THEORY OF THE MASS SPECTROGRAPH. 3 



227 



Positive rays obtained from an ordinary discharge bulb vary both 

 in mass and velocity. An electric field will spread them into an 



" electric spectrum " with deflections proportional to ^ ; a mag- 

 netic field will spread them into a "magnetic spectrum" with de- 



c 

 flections proportional to . * * * 



The concentration of the stream of positive rays down the axis 

 of the discharge bulb is very marked, but there is good evidence for 

 assuming that the intense part of the stream occupies a fairly con- 

 siderable solid angle. This suggests the possibility of an increase of 



s, 



s, 



Fig. 1. — Theory of the mass-spectroscope. 



intensity by means of a device which should select the rays aimed at 

 a particular spot on the plate whatever direction they come from. 

 * * * 



Clearly the simplest way of increasing the intensity of the spot 

 without increasing its dimensions, at any rate in one direction, is to 

 use two parallel straight slits. * * * 



POSSIBILITIES OF FOCUSING POSITIVE RATS. 



The very great accuracy attained in' the spectrometry of light 

 depends largely on the fact that a considerable solid angle of diver- 

 gent rays from a point source can be brought to a point image by 

 means of a lens. It is of importance to inquire if any such con- 

 vergence can be applied to rays of charged particles by any electric 

 or magnetic device. * * * 



3 Extracted from "A positive ray spectograph," Philosophical Magazine and Journal of 

 Science, December, 1919, pp. 707-714. 



