PHOTOGRAPHS IN NATURAL COLORS, BY THE PROCESS 



OF L. LUMIERE.* 



By Leon Wakneuke. 



About two years ago Prof. Lippmauu, of the Sorbouue, at Paris, 

 succeeded iu producing- photograpliically a colored image of the sohir 

 spectrum, based on the well-known priuci]>les of interference. He used 

 for that purpose a plate coated with au albumen, collodion, or gelatin 

 sensitive film. This sensitive film was during exposure brought into 

 contact with metallic mercury, the image of the spectrum being pro- 

 jected on the film, through its glass support. The light, after i)euetrat- 

 ing through the thickness of the film, was reflected back from the sur- 

 face of the mercury, the direct light waves encountering the waves of 

 reflected light, producing the i^heuomeuon of interference in the thick- 

 ness of the film. The waves of light propagating iu opposite direc- 

 tions cause the vibrations at certain intervals to be neutralized, while 

 at others they are intensified. H' such a plate could be developed, 

 fixed, and dissected, we should find it to consist of strata of the black 

 deposit of silver, produced by the developer in the parts corresponding 

 with the maximum of light succeeded by transparent strata, correspond- 

 ing to the minimum of light, where the developer had no action. The 

 distance between the strata is equal to half the wave length, which is 

 600 ten-thousandths of a millimeter for red light, 583 for orange, 551 

 for yellow, 475 for blue, and 423 for violet. In a film of tA millimeter 

 thickness there will be about 200 such strata. It is evident that on 

 examining such a plate by refiected light we should observe the colors, 

 because it is formed of a series of films of the thickness requisite to 

 produce color sensations. 



Subsequent experiments proved that by using a gelatin film, sensi- 

 tised with a chromium salt, a similar result is obtaineu, the action of 

 interference producing strata of soluble and insoluble gelatin. 



The exposure of the plates produced by Lippmann was very long, 

 and, owing to the variation of sensitiveness of different rays of the 

 spectrum, necessitated the masking of the i^ortions exi^osed to the more 

 actinic rays while the others are exposed. L. Lnmiere succeeded in 

 producing colored images in one operation, and in last May, in a paper 



*Eead before the Photographic Society of Great Britain, October 11, 1893 {Journal 

 and Transactions of Phot. Soc. G. B., Oct. 28, 1893; vol. xviii, pp. 52-51). 



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