1887.] Dissociation of Gases by the Electric Discharge. 343 



Dawson (G. M.) Notes to accompany a Geological Map of the 

 Northern Portion of the Dominion of Canada. 8vo. Montreal 

 1887; On certain Borings in Manitoba and the North-West 

 Territory. 4to. Montreal 1887. The Author. 



Dawson (Sir J. W.), F.R.S. On the Fossil Plants of the Laramie 

 Formation of Canada. 4to. [Montreal'] 1886. The Author. 



Dubois (A.) Description de Deux Nouvelles Especes d'Oiseaux. 

 8vo. [Bruxelles] 1887. The Author. 



Hughes (F. J.) Supplement to "Harmonies of Tones and Colours 

 developed by Evolution." 4to. London 1885. The Author. 



Marsh (0. C.) American Jurassic Mammals. 8vo. [New Haven] 

 1887. The Author. 



Martone (M.) Sopra un Problema di Analisi Indeterminata. [Two 

 copies.] 8vo. Catanzaro 1887. The Author. 



May 26, 1887. 



Professor G. G. STOKES, D.C.L., President, in the Chair. 



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

 for them. 



Professor Archibald Liversidge (elected 1882) was admitted into 

 the Society. 



The following Papers were read : — 



I. The Bakerian Lecture. — " On the Dissociation of some 

 Gases by the Electric Discharge." By J. J. THOMSON, M.A., 

 F.R.S., Fellow of Trinity College, and Cavendish Professor 

 of Experimental Physics in the University of Cambridge. 

 Received May 26, 1887. 



(Abstract.) 



The gases considered are iodine, bromine, chlorine, and nitrogen 

 tetroxide. The effects of the spark on iodine and bromine were in- 

 vestigated in two ways. In the first method the iodine was placed in 

 a tube from which the air had been exhausted, and which was 

 furnished with a gauge which served to measure the changes of 

 pressure in the tube. The liquid in the manometer was sulphuric 

 acid, and in order to avoid any disturbance due to the absorption of 



