* I Prof. J. J. Thomson. On the Propagation of the [Jan. 15, 



Kevue Scientifique. Juillet De*cembre, 1890. 4to. Paris. 



The Editor. 

 Symons's Monthly Meteorological Magazine. July to December, 



1890. 8vo. London. Mr. G. J. Symons, F.R S. 



Zeitschrift fur Biologie. Bd. XXVII. Heft 2-3. 8vo. Miinchen 



1890. The Editors. 



Mezzotint Engraving of Sir W. Bowman, Bart., F.R.S., from the 

 painting by W. W. Ouless, R.A., exhibited at the Royal 

 Academy, 1889. The Committee of Subscribers. 



January 15, 1891. 

 Sir WILLIAM THOMSON, D.C.L., LL.D., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The following Papers were read : 



I. " On the Rate of Propagation of the Luminous Discharge 

 of Electricity through a Rarefied Gas." By J. J. THOM- 

 SON, M.A., F.R.S., Cavendish Professor of Experimental 

 Physics, Cambridge. Received January 2, 1891. 



Though the determination of the velocity of propagation of the 

 luminosity which accompanies the electric discharge through gases 

 might well be expected to throw considerable light on the means by 

 which the discharge is effected, as far as I can find, no attempts 

 seem to have been made in this direction since Wheatstonc, in 1835, 

 observed the appearance presented in a rotating mirror of the dis- 

 charge through a vacuum tube 6 feet long ; he concluded from his 

 observations that the velocity with which the flash went through the 

 tube could not have been less than 2 x 10 7 cm. per second. This 

 very great velocity does not seem to be accompanied by a corre- 

 spondingly large velocity of the luminous molecules, for von Jahn 

 (Wiedemann's 'Annalen,' vol. 8, 1879, p. 675) has shown that the 

 lines of the spectrum of the gas in the discharge tube are not dis- 

 placed by as much as 1/40 of the distance between the D lines when 



