1896.] Professor Lippnann on Colour Photography. 151 



WEEKLY EVENING MEETING, 

 Friday, April 17, 1896. 



Sir James Ckichton-Browne, M.D. LL.D. F.R.S. Treasurer and 

 V ice-President, in the Cliair. 



Professor G. Lippmann, Membre de I'lnstitut (France). 

 Colour Photography, 



The problem of colour photography is as old as photography itself. 

 The desire of fixing the colours as well as the design of the beautiful 

 image thrown on the screen of the camera, very naturally occurred to 

 the earliest observers. Since the beginning of this century three 

 distinct solutions of the problem have been realised. 



The first solution, not quite a complete one, is founded on the 

 peculiar properties of a silver compound, the violet subchloride of 

 silver. E. Becquerel (1860) converted the surface of a daguerreotype 

 plate into this silver compound, and by projecting on it the image of 

 the solar spectrum, and other objects, obtained good coloured impres- 

 sions. Poitevin substituted paper for the silver plate as a substratum. 

 No other substance has been discovered that can play the part of the 

 subcbloride of silver. Moreover the image is not fixed, in the photo- 

 graphic sense of the word ; that is, the coloured impression is retained 

 for any length of time in the dark, but it is blotted out by the action 

 of daylight. The reason of it is this : the Becquerel images are 

 formed by coloured silver compounds, which remain sensible to light ; 

 so that they are destroyed by the continued action of light, in virtue 

 of the same action which gave them birth. Despite the numerous 

 experiments made by Becquerel, Poitevin, Zenker and others, no 

 substance has been found that is capable of destroying the sensibility 

 of the subchloride for light without at the same time destroying its 

 colour. 



The second method for colour photography is an indirect one, 

 and may be called the three-colour method. It was invented in 

 France by Ch. Cros, and at the same time by M. Duces du Hauron 

 (1869). German authorities claim the priority of the idea for Baron 

 Bonstetten. Three separate negatives (colourless) are taken of an 

 object through three coloured screens. From these three positives 

 (equally colourless) are made ; and, lastly, the colour is supplied to 

 these positives by means of aniline dyes or coloured inks. Thus 

 three coloured monochromatic positives are obtained, which by super- 

 position give a coloured image of the model. In the ingenious 

 process lately invented by Prof, Joly, the three negatives, and appa- 



