202 Mr. A. Claiidet on the Actions of the red and 



live and had ac(]iiired their continuing action, at a period cor- 

 responding to the present? 



Having made my experiments with the greatest care, I 

 seize with satisfaction this manner of explaining phaenomena 

 apparently contradictory. It would indeed be curious and 

 interesting to find that neither myself nor the other experi- 

 menters are in error, and that vve differ only as regards con- 

 ditions and circumstances, which, without our knowledge, have 

 exercised an influence upon our experiments. But there can 

 be no doubt as regards the iodized plate, when it has been 

 subsequently submitted to the vapour of bromine alone, or of 

 bromine and chlorine united. I have operated with these 

 substances during the various periods of the year, and I have 

 invariably found that the red, orange, and yellow glasses de- 

 stroy the action of daylight*. 



This arises perhaps from the high degree of sensitiveness 

 of all the coatings containing bromine. During the periods 

 of the year when, by the intensity and purity of daylight, the 

 simple iodide of silver has acquired the maximum of sensitive- 

 ness, it may be affected like the bromo-iodide, which, being 

 about 100 times more sensitive, is always capable of receiving 

 the destructive action of the less refrangible rays. Then it 

 would appear that the destructive action of these rays require 

 a- hio;hly sensitive coating to become manifest. 



This manner of viewing t!;e question is corroborated by a 

 curious phaenomenon, in other respects very interesting^, and 

 which 1 think has hitherto escaped the researches of photo- 

 graphers, I intended to treat this subject at some length in 

 a separate paper, but I cannot do better than make use of this 

 tact on the present occasion, and 1 shall therefore not defer its 

 publication. 



There exists a coating of iodide of silver which is twenty- 

 five times more sensitive than the coating of Daguerre. Da- 

 guerre did not imagine that his process was susceptible of such 

 a degree of sensitiveness. What an unexpected result at the 

 time of his discovery ! It is to be regretted that it escaped 

 the inventor of the Daguerreotype, and that it did not precede 



* I must here state, that consiclerinj; the Daguerreotype pinte as now 

 exclusivel}' prepared with bromine in acldition to iodine, I have paid ninth 

 more attention to this combination than to the original and now obsolete 

 preparation of Daguerre containing only iodine; and I have had the op- 

 portunity of experimenting on plates prepared with iodine and bromine, 

 and with iodine, bromine, and chlorine during a whole year, in all seasons; 

 so that if there might exist any uncertainty as to the destructive effect of 

 red and yellow glasses on silver plates simply iodized, there can be no doubt 

 as to the permanency of the destructive effect on the bromo-iodized pla' 

 with or v.'ithout chlorine, in every season and in all circumstances. 



