xxx. Chemical Section. [November 28th, 1919. 



atmosphere to blue light ; the eye sees further because it is 

 more sensitive to red than to blue. Obviously, if a distant 

 scene could be photographed in red light only, the picture 

 would reveal much more detail because of the cutting off of 

 the haze owing to the greater penetrating power possessed by 

 red light in a clear atmosphere. 



With these considerations in mind the experimental inves- 

 tigation of sensitising dyestuffs was instituted in the chemical 

 laboratories of the University of Cambridge by Dr. W. H. Mills 

 and myself at the end of 1914. Methods for producing the 

 ordinary sensitising dyestuffs on a technical scale were devised, 

 and all the sensitisers used by the Allies have been prepared in 

 the Cambridge laboratories since the German importation 

 ceased. Our photographic air-service was non-existent at the 

 outbreak of war; it was slowly built up until it ultimately 

 became of great magnitude and attained a high efficiency. It 

 started by using ordinary blue-sensitive plates, but at the date 

 of the Armistice some 80 per cent, of the plates used were red- 

 sensitive or pan-chromatic plates. 



The best panchromatic plate made in pre-war days possessed 

 about one-third the sensitiveness to red as to blue light. At 

 the present time a very rapid panchromatic plate is on the 

 market which is much faster to red than to blue light ; the 

 rapidity of the plate to red light has been thus increased about 

 four-fold. The advantages to be gained by the skilful use of 

 the present highly-perfected panchromatised plates in our 

 photographic air service, in the circumvention of camouflage 

 colour schemes, and in the photography of distant scenes in 

 spectroscopically pure light, are among the most important 

 studies of the new service. The peace applications of pan- 

 chromatic plates will undoubtedly multiply rapidly. A number 

 of lantern slides were shown illustrating the points referred to 

 above. 



The chief processes at present available for the photographic 

 reproduction of the colours of parti-coloured objects were then 

 explained and examples of each were exhibited. 



General Meeting, November 28th, 1919. 

 Mr. R. H. Clayton, B.Sc, in the Chair. 



It was resolved that the Officers of the Chemical Section be 

 as follows :— R. H. Clayton, B.Sc. (Chairman); J. H. Lester. 

 M.Sc, F.I.C. (Hon. Treasurer); F. W. Atack, M-ScTech., 

 B->Sc (Hon. Secretary) ; and the Members of the Committee : -.- 



