Spectra in Compound Gases, 733 



high temperature. The effective temperature at the cathode 

 is higher than the effective temperature at the anode. 



(3) In general (though not always) the cathode spectrum 

 is seen throughout the negative glow, whilst the anode 

 spectrum is found all along the positive column. 



(4) The current can be carried through the tube inde- 

 pendently of ordinary matter, viz. bv corpuscles ; and hence 

 pure electrolysis is impossible. We cannot expect to find 

 Faraday's laws obeyed. 



It is perhaps legitimate to go so far as to say that in all 

 probability positive ions move under the influence of the 

 electric force towards the cathode, and negative ions towards 

 the anode, as in the case of liquid electrolysis. If the usual 

 theory of the production of spectra be accepted (i. e. that 

 the essence of the process is the discharge of ions), it must 

 be supposed that the discharge of positive ions takes place 

 throughout the negative glow, whilst negative ions lose their 

 charges in the positive column. If we then consider the 

 process to be analogous to electrolysis of solutions, we must 

 regard the whole negative glow as constituting the cathode, 

 and the positive column as equivalent to the anode. 



Summary. 



It has been found that when an electric discharge is passed 

 through a gas at low pressures the spectrum of the glow 

 around the cathode differs from that of the light from the 

 neighbourhood of the anode. In compound gases the spectra 

 which appear at the cathode are due to atoms which, from 

 chemical considerations, must be supposed to carry a positive 

 charge. Similar remarks apply to the anode. It is thought 

 that the principal factors which determine the differences in 

 the spectra at the two electrodes are : — 



(1) The difference in temperature and electric force at the 

 two poles. 



(2) Ihe electrochemical character of the elements concerned. 



These experiments have been conducted throughout in the 

 Cavendish Laboratory under the direction of Professor Sir 

 J. J. Thomson, whom I take this opportunity to thank for 

 his numerous suggestions and kindly interest in the work. 



Cavendish Laboratory, Cambridge. 

 July 6th, 1911. 



Phil. Mag. S. 6. Vol. 22. No. 131. Nov. 1911. 3 C 



