1878.] Capt. Abney on the Acceleration of Oxidation, Sfc. 291 



some hours. When cold, and just taken out of the sand, they were 

 found to be inactive (except that they liberated a portion of the modi- 

 fied salt after the manner of the inactive essential oils) ; but by 

 exposure to the outer air (wind N.E.) they became active in about ten 

 minutes. Cocoa-nut shell charcoal requires a longer exposure to become 

 active. 



Hence the activity of charcoal does not depend on absorption, but 

 on the condition of the air contained within its pores. 



IV. "Notes on Physical Geology." By the Rev. Samuel 

 Haughton, M.D. Dublin, D.C.L., Oxon, F.R.S., Professor of 

 Geology in the University of Dublin. 



April 11, 1878. 

 Dr. W. FARE,, Vice-President, in the Chair. 



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

 them. 



Dr. William Carmichael Mcintosh was admitted into the Society. 

 The following Papers were read : — 



I. " The Acceleration of Oxidation caused by the Least Re- 

 frangible End of the Spectrum." By Captain Abney, R.E., 

 F.R.S. Received March 16, 1878. 



Preliminary Note. 



In a paper contributed to the Philosophical Magazine in January last, 

 I expressed an opinion that Chastaing's idea regarding an acceleration 

 of oxidation being caused by red light might prove true in regard to the 

 oxidation of the photographic image, and elsewhere* that Becquerel's 

 coloured spectra and Draper's reversed spectra might be explained on 

 the same principles. Owing to want of time until this last week, I 

 have been unable to investigate the matter, but can now affirm that 

 such is the case as regards oxidation of the photographic image. 



Silver bromide, free from contamination, emulsified in collodion, 

 which had been previously carefully purified, was spread on a plate, 



* " Treatise on Photography." Longmans. Page 225. 



