452 Dr. F. W. Aston on the 



Evidence of the Positive Bay Spectrograph. 



The " mass-spectra " yielded by the new method of positive 

 ray analysis recently described (F. W. Aston, Phil. Mag. 

 Dec. 1919J supply these measurements in an entirely satis- 

 factory manner. Plate IX. A, B, 0, D, are prints from 

 negatives obtained by means of this apparatus. Each 

 contains a number of spectra taken with different electric 

 and magnetic fields ; the following table of values of P the 

 potential between the electrostatic plates in volts, I the 

 current passing through the magnet in amperes, and T 

 the time of exposure in minutes, is given for reference : — 



Table I. 



1 



2 3 



4, 



5 



1 



o 



o 



4 



5 



P= 240 



210 240 



320 



320 



320 



320 



360 



240 



240 



I—130 



•450 -600 



•600 



•800 



•351 



•600 



■600 



•600 



•]73 



T= 4 



10 10 

 C 



10 



10 



15 



15 



15 

 D 



15 



4 



12 3 4 5 6 12 3 4 5 6 



P= 240 240 280 320 360 360 320 320 320 320 320 320 



I =-380 -550 -550 "550 '550 -700 -482 -520 "554 -606 -701 '798 



T= 15 15 15 15 15 10 10 10 10 10 10 10 



On the left of each spectrum can be seen the small circular 

 dot photographed on the plate just before or during the 

 exposure, this is used as a register spot for measuring- 

 purposes. 



Plate A was taken with carbon monoxide. That is to say, 

 the vacuum in the discharge-tube was maintained by 

 continual pumping with a Graede rotating mercuiy pump 

 against a small leak of CO. It must be understood that 

 this does not imply that the contents of the discharge-bulb 

 were pure CO, since the use of tap-grease and wax joints 

 necessitates the presence of hydrocarbons, etc., but at least 

 one can be certain that the quantity of neon present was 

 negligible as none had yet been put into the apparatus. 

 The electric deflexion is away from the register spot, the 

 magnetic towards it, so that the heavier musses are to the 

 right of lighter ones. 



Spectrum A I. was taken with a very small magnetic field 

 showing the lines due to the hydrogen atom and molecule. 

 In AIL the field has been increased and a group of five 

 lines are seen. These, which may be called the Cx group, 

 are 12-C, 13-CH, 14-CH 2 (or N), 15-CH 3 , 16-CH 4 (or O). 



