200 Mr. A. Claudet on the Actions of the red and 



a new memoir on the subject, at tlie same time tr^^ing to ex- 

 plain the anomaly existing between Messrs. Ed. Becquerei 

 and Gaudin's experiments and my own. 



As persons interested in these questions migl.'t only read 

 my paper to the Royal Society, which you have inserted in 

 full in the last Number of the Philosophical Magazine, I con- 

 sider it my duty to publish immediately what has passed he- 

 fore the Academic des Sciences in reference to my communi- 

 cation ; and I shall be much obliged if you will allow me a 

 place in your pages for the insei'tion of the following transla- 

 tion of my new memoir to the Academic des Sciences, which 

 has been read at the meeting of the 20th of December. (See 

 Comptes Rendus.) 



I have the honour to be, Gentlemen, 



Your most obedient Servant, 



A. Claudet. 



1 have again examined my former experiments, and I find 

 some specimens which show that red and yellow glasses have 

 destroyed the effect of the photogenic light on plates simply 

 iodized. How can this fact be reconciled with Messrs. Ed. 

 Becquerei and Gaudin's experiments, and those I had just 

 made in consequence of these philosophers' observations? Had 

 I made any mistake in the classification of my former speci- 

 mens, or had I erred in my mode of operating? This might 

 be, and I feared such was the case, as I just (.btained quite 

 different results. I then questioned my assistant, and he re- 

 collected well that we had repeatedly experimented upon plates 

 simply iodized, and that we had then found that red and yel- 

 low glasses did destroy the action of daylight, as well on 

 iodized plates as on those which had been submitted to the 

 compound vapour of iodine and bromine. 



I then recollected a curious fact mentioned by Dr. Draper 

 of New York (see Phil. Mag., Feb. 1847, pages 89 and 90), 

 which at the time of its publication I had found so inexplicable 

 that I did not pay much attention to it, and which I had 

 totally forgotten during the ciiurse of my experiments. 



Dr. Draper said, " Such are the facts 1 observed, and they 

 seem to have been reproducetl by MM. Foucault and Fizeau; 

 but there are also others of a much more singular nature. In 

 these Virginia specimens the same portecUng action reappeais 

 beyond the violet. 



" The only impressions in which I have ever seen this pro- 

 tecting action beyond the violet, are those made in Virginia in 

 18i2; they were made in the month of July. Struck with 



