235 



President. The Lord Wrottesley, M.A. 

 Treasurer. Major-General Edward Sabine, R.A., D.C.L. 



f William- Sharpey, M.D. * 

 ~ LGeorge Gabriel Stokes, Esq., M.A., D.C.L. 

 Foreign Secretary. William Hallows Miller, Esq., M.A. 

 Other Members of the Council. James Moncrieff Arnott, Esq. ; 

 William Benjamin Carpenter, M.D. ; Arthur Cayley, Esq. ; The Very 

 Rev. The Dean of Ely; William Fairbairn, Esq. ; Arthur Farre, M.D.; 

 William Robert Grove, Esq., M.A. ; Joseph Dalton Hooker, M.D. ; 

 William Hopkins, Esq., M.A. ; William Allen Miller, M.D. ; Lyon 

 Playfair, Esq., C.B., Ph.D. ; Rev. Bartholomew Price, M.A. ; Sir 

 James Clark Ross, Capt. R.N., D.C.L.; Rear-Admiral W. H. Smyth, 

 D.C.L. ; John Stenhouse, LL.D. ; John Tyndall, Esq., Ph.D. 



Mr. Grove, Dr. Hooker, Mr. Hopkins, Sir James C. Ross, and 

 Dr. Tyndall were elected Auditors of the Treasurer's Accounts on 

 the part of the Society. 



The reading of Professor BUNSEN and Dr. HENRY ROSCOE'S 

 Paper " On the Measurement of the Chemical Action of Light," was 

 resumed and concluded. 



(Abstract.) 



The only instrument which has been applied to the measurement 

 of the chemical action of light was proposed in 1843 by Dr. Draper 

 of New York. The sensitive substance employed by him was a 

 mixture of chlorine and hydrogen, and by measuring the diminution 

 ensuing on exposure to light, he experimentally determined some 

 important relations of photo-chemical action. Draper's instrument 

 is, however, not adapted for accurate measurements, owing, in the 

 first place, to the fact that the gas is subject to varying pressure ; 

 and, in the second place, that the statical equilibrium, which must 

 exist between the free and dissolved gases, in order that the free gas 

 should consist of equal volumes of chlorine and hydrogen, was never 

 approached. 



In order to obtain more accurate results than was possible with 

 Draper's tithonometer, we sought for means of preparing a gas con- 

 taining equal volumes of chlorine and hydrogen ; this means was 

 found, notwithstanding Draper's contrary statement, in the electro- 



