NATURAL PHILOSOPHY. 133 



different tints, passing gvadualh" from an opaque white to a black 

 tint. He also observed that the tint best suited to obtain favorable 

 results was when the jDlate had acquired a pearlish pink; and, 

 although he found that the plate so prepared, when placed in the 

 camera obscura, assumed the colors composing the si^ectrum, 

 still they were faint ; but he remedied this defect of intensity of 

 tints by heating for several hours to a temperature of 95° to 100° 

 the chlorinated plate, and then submitting it to the influence of 

 the various colors composing the spectrum. Further, in the 

 course of his studies, he made the important observation that he 

 could replace the peculiar action of heat on his prepared daguer- 

 reotype plate, by exposing it to the rays of the sun under a sheet 

 of paper which had been steeped in an acid solution of suljiliate 

 of quinine. The effect of this was that the plate of silver as- 

 sumed an intense white color, nearly resembling that of paper; 

 while if the jsrotective paper had not been used, the silver plate 

 would have gradually acquired a dark tint, and would have lost 

 the whole of its sensitive properties, the protective paper having 

 the power of arresting completely the most refrangible rays of 

 light, especially those which are beyond the line H of the spec- 

 trum. Notwithstanding M. Edmund Becquerel's ardent hopes to 

 find a method which would enable him to fix on a sensitive sur- 

 face the various colors of the spectrum, still he failed ; for they 

 faded as soon as they were exposed to the direct rays of light, 

 and could only be preserved in obscurity. But there is one gen- 

 tleman who deserves great praise for the extraordinary persever- 

 ance which he has shown in this class of investigation. I mean 

 the nephew of the discoverer of photography, M. Niepce de Saint 

 Victor. Although I Avill not enter here into the details of these 

 valuable researches, as they can be found in the " Comptes Rendus 

 de I'Academie des Sciences," still I may just be allowed to state 

 that he has not only by the following process obtained far more 

 brilliant colors than those first produced by M. Becquerel, but 

 has succeeded in rej^roducing on sensitive plates the various 

 colors of colored surfaces, such as are presented by fabrics, 

 flowers, etc. ; and, fui'ther, he has lately been so fortunate as to 

 reproduce on his plates yellow and black tints, which had resisted 

 all previous attempts. To give you an idea of the facts arrived 

 at by this gentleman, I may state that he has succeeded in so 

 fixing upon sensitive surfaces the various colors of the spectrum, 

 or of colored surfaces, that they will bear the action of diffused 

 light for several days. In fact, I have seen photographs which 

 reproduce faithfully a small doll dressed up in various colors, and 

 in which even the most minute ornament could be traced ; and, 

 what is certainly not less interesting, was the reproduction of the 

 iridescent colors of the peacock's feather. To obtain these mar- 

 vellous results, M. Niepce de Saint Victor takes a daguerreotype, 

 or silver-coated plate, and dips it into a weak solution of hj^po- 

 chlorite of sodium, having a siDccific gravity of 1.35, until it has 

 assumed a bright pinkish hue. The plate is then covered with 

 a solution of dextrine, saturated with chloride of lead ; it is then 

 dried, and subsequently submitted to the action of heat, as in M. 

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