xxviii. Chemical Section. [October 24th, 1919. 



PROCEEDINGS 



OF 



THE MANCHESTER LITERARY AND 

 PHILOSOPHICAL SOCIETY 



CHEMICAL SECTION. 



Ordinary Meeting, October 24th, 1919. 



Sir Henry A. Miers, M.A., D.Sc, F.R.S., Vice-Chancellor of 

 the Victoria University of Manchester, in the Chair. 



At the Opening Meeting of the newly formed Chemical 

 Section of the Society, Professor Sir William J. Pope, M.A., 

 D.Sc, LL-D., F.R.S., Professor of Chemistry in the University 

 of Cambridge, gave an Address on "The Photography o( 

 Coloured Objects.'' 



The ordinary photographic plate is sensitive only to blue 

 and violet light and not to red or yellow. The plate thus 

 receives much the same impression of a parti-coloured scene 

 focussed upon it as we should receive on viewing the scene 

 through deep blue spectacles. The livefy discussions concerning 

 the claims of photography as an artistic medium which were 

 fashionable some twenty years ago centred in reality about this 

 limitation of sensitiveness of the ordinary photographic plate ; 

 no method of pictorial reproduction which rendered the yellow 

 narcissus and the bright red General Mc Arthur rose as black, 

 whilst showing the violet as white, can be described as artistic. 

 The prime requisite of any photographic process for the repre- 

 sentation of parti -coloured objects is obviously that the photo* 

 graphic plate used should be sensitive to light other than the 

 blue and violet; given a plate which is acted upon by light 

 from any part of the visual spectrum many devices become 

 applicable for the production of a satisfactory presentment in 

 monochrome of the coloured object or for the reproduction of 

 the actual component colours. 



The first truly scientific appreciation of this principle was 

 stated by Clerk Maxwell, the first Cavendish Professor in the 

 University of Cambridge, who in 1861 exhibited three photo- 

 graphs of a tartan ribbon taken through red, green and blue 



