On the Masses of the Ions in Gases at Low Pressures. 547 



Table IV. — Selected Fusing and Boiling Points on the 

 Proposed British Association Scale. 



Substance. 



F.P. 



2319 

 269 2 

 320-7 

 327-7 

 419-0 

 629-5 

 654-5 



Substance. 



B.P. 



Tin 





1841 



218-0 

 305-8 

 356-7 

 414-5 



758 

 916 















Sulphur 



idmium 





Zinc 







My thanks are due to several Members of the Electrical 

 Standards Committee of the British Association and others, 

 who have kindly revised the proofs of this article. 



LVIII. On the Masses of the Ions in Gases at Low Pressures. 

 By J. J. Thomson, M.A., P.E.S., Cavendish Professor of 

 ■ Experimental Physics, Cambridge*. 



IN a former paper (Phil. Mag. Oct. 1897) I gave a deter- 

 mination of the value of the ratio of the mass, m, of the ion 

 to its charge, e, in the case of the stream of negative electrifica- 

 tion which constitutes the cathode rays. The results of this 

 determination, which are in substantial agreement with those 

 subsequently obtained by Lenard and Kaufmann, show that 

 the value of this ratio is very much less than that of the 

 corresponding ratio in the electrolysis of solutions of acids 

 and salts, and that it is independent of the gas through which 

 the discharge passes and of the nature of the electrodes. In 

 these experiments it was only the value of m/e which was 

 determined, and not the values of m and e separately. It was 

 thus possible that the smallness of the ratio might be due to 

 e being greater than the value of the charge carried by tlia 

 ion in electrolysis rather than to the miss in being very 

 much smaller. Though there were reasons for thinking 

 that the charge e was not greatly different from the electro- 

 lytic one, and that we had here to deal with masses smaller 

 than the atom, yet, as these reasons were somewhat indirect, I 

 desired if possible to get a direct measurement of either m or 

 e as well as of m/e. In the case of cathode rays I did not 



* Communicated by the Author : read at the Meeting of the British 

 Association at Dover. 



