PHOTOGRAPHY IN THE OOLORW OF NATURE. 153 



The projuress by wliicli sucli imperfect results luive been obtained is 

 too slow to be applied sucessfully to eamera pliotography, and the 

 results are not permanent. 



In view of all these facts, it would appear that there is no scientitic 

 basis for a belief that any material improvement can ever be made in 

 this process, and that all so-called progress along- this line is a delu 

 sion. It is true that some distinguished photographic writers continue 

 to regard every new modification of this ohl process, and every new 

 result of experiment with it, as another stei> towards the ])hotographic 

 re-production of the natural colors ; but I have no doubt that if the 

 same writers had lived two hundred years ago they would have regarded 

 the production of new yellow colored metal alloys as steps toward the 

 transmutation of the baser metals into gold. 



In my opinion, the iirst step toward the solution of this problem was 

 taken by Henry CoUen, (j)ueen Victoria's painting master, who, in 18G5, 

 invented a plan of composite heliochromy. His plan was based upon 

 a false conception of the nature of color, and means for carrying it out 

 were then unknown ; but it was a bright idea, and contained the germ 

 of a successful process. Collen's original communication of his idea 

 appeared in Tin- Brifixh Jounuil of Photof/ropJiij, October 27, ISCto, and 

 reads as follows: 



"It occurred to me this morning that if substances were discovered 

 sensitive only to the primary colors — that is, one substance to each 

 color — it would be i)ossible to obtain photograi>hs with the tints as m 

 nature by some such means as the following: 



'•Obtain a negative sensitive to the blue rays only; obtain a second 

 negative sensitive to the red rays only, and a third sensitive to the yel- 

 low rays only. 



"There will thus have been three plates obtained for printing in 

 colors, and each plate liaviug extracted all its own peculiar color from 

 every part of the subject in which it has been combined with the other 

 two colors, and being in a certain degree analogous to the tones used 

 in chromo-lithography. Now, it is evitlent that if a surface be prepared 

 for a positive picture, sensitive to yellow rays only, and that the two 

 negatives, sensitive only to blue and ied,be super imposed either on the 

 other, and be laid on this surface, the action of light will be to give all 

 the yellow existing in the subject, and if this process be repeated on 

 other surfaces sensitive only to red or blue, respectively, there will 

 have been produced three pictures of a colored object, each of which 

 contains a primitive color reflected from that object. 



"Now, supposing the first great object achieved, viz., the discovery 

 of substances or preparations, each having sensitiveness to each of the 

 l)rimary colors only, it will not be difficult to imagine that the nega- 

 tives being received on the surface of a material quite transparent and 

 extremely thin, and that being so obtained are used as above, /. e., each 

 l)air of superimposed negatives to obtain the color of the third^that 

 three positives will be obtained, each representing a considerable por- 

 tion of the form of the object, but only one iirimary of the decomposed 

 color of it. Now, if these three positives be received on the same kind 

 of material as that used for the negatives and be then laid the one on 

 the other, with true coincidence as to the form, and all laid upon a 



