THE PROBLEM OF PHOTOGRAPHY IN COLOR. 531 



THE PROBLEM OF PnOTOGRAPHT IN COLOE. 



By OGDEN N. rood, 

 pe0fes30k of physics in columbia college. 



MY attention was first called to this subject in 1853. At that time 

 I was an assistant in the " Yale Analytical Laboratory," which 

 afterward developed into the present Shefiield School. The interest 

 of the Professor of Chemistry, John Porter, was excited by some arti- 

 cles on this subject which had recently appeared in France, and he 

 was desirous of making experiments to test an idea that had occurred 

 to himself. The sensitive surface was to be prepared while actually 

 under the influence of colored light, so that from the start the colored 

 rays should be able to act on it and influence the molecular condition 

 of the newly formed combinations. A prismatic spectrum was to be 

 employed, and it was hoped that the red rays would persuade the 

 newly born silver salts to reflect red light and only red light, while 

 the same salt, when generated under the influence of the green rays, 

 by the aid cf this early education was to be made capable hereafter of 

 reflecting green light, but incapable of reflecting red, yellow, or blue 

 light. Expressed in the language of the undulatory theory of light, 

 the idea would be about as follows : expose molecules in act of forma- 

 tion to the long waves of red light, and ever after they will be capable 

 of reflecting mainly the long waves of red light ; all other kinds they 

 will absorb and convert into heat. 



This task having been assigned to me, I entered on it with zeal, and 

 arranged a dark room ; the solar spectrum was made to fall nicely on 

 the table, and many of the processes known at that time were in suc- 

 cession tested. The photographs of the spectrum thus obtained were 

 not at all uniform in color ; sometimes they would be delicately shaded 

 from a dull-red gray to a blue or violet-gray and often they presented 

 minor changes of color variously disposed. Favorable indications were 

 followed up as they presented themselves ; but after a time I became 

 convinced that the play of color in the photographs was solely due to 

 the greater or less energetic action of the light upon the sensitive sub- 

 stance, and that exactly the same results could be obtained by using 

 white light, more or less intense. When the work was finished, I pre- 

 sented my written report witb the photographs, and the professor, 

 after studying it, came to the same conclusion. The " nascent " idea 

 was not feasible. 



And yet photographs in color of colored objects have been ob- 

 tained. Upon one occasion, about twenty-five years ago, I obtained 

 a very fine one. The subject was a large elm-tree and a red farm- 

 house, these two objects filling up almost the whole plate. The ordi- 

 nary wet-collodion process was employed ; the negative, after being 



