Action of Red and Yellow Rays on Dagtierrotype Plates. 1 99 



At all incidences, and in all azimuths within the shaded 

 portions of the figure ZAZD, DCBC, the vchite-coitrcd rings 

 are seen. At all azimuths and incidences corresponding with 

 the outlines of the curves ZDZ, DCBC, the rings disappear; 

 and at all azimuths and incidences without the shaded portions 

 of the figure, the black-centred rings are seen*. 



St. Leonard's College, St. Andrews, 

 April 8, 1841. 



XXX. Photographic phcenomena referringto the various Actions 

 of the red and yelloxo Rays on Daguerreotype Plates "when 

 they have been affected by daylight. By A. Ci.au det, Esq. 



To the Editors of the Philosophical Magazine and Journal. 



Gei'tli;?,ien, 

 tJAViNG made on the 24.th of October 1847, a commu- 

 ^^ nication to the .Academie des Sciences of Paris similar 

 to that I sent on the lOlh of June to the Royal Society, On 

 different Properties of Solar Radiation acting on Silver Plates 

 coated with Iodine, or its compounds with Bromine or Chlo- 

 rine, a discussion ensued, in which Messrs. Ed. Becquerel and 

 Gaudin (see Comptes Rendus, Oct. SI and Nov. 2) controverted 

 the accuracy of some part of my experiments. I had stated 

 that the red and yellow glasses had the property, as well as 

 the pure red and yellow rays of the spectrum, of destroying 

 the photogenic action produced by daylight on silver })iates 

 coated with iodine, or its compounds with bromine and chlo- 

 rine ; Messrs. Ed. Becquerel and Gaudin asserted that the 

 red and yellow glasses had not the property of destroying, 

 l)ut of continuing the action commenced by daylight on the 

 simply iodized plate. 



As soon as I was apprised of the remarks made by Messrs. 

 Becquerel and Gaudin, 1 repeated the experiments, and to 

 my great surprise 1 found that the destructive action of the 

 red and yellow glasses did not appear, on this trial, to extend 

 to the simply iodized, but only to the bromo-iodized plate. I 

 lost no time in communicating to the Academic des Sciences 

 the result of these experiments ; and at the meeting of the 

 2'2nd of November my letter stating the apparent contradiction 

 was read. 



This led me to continue the experiment, in order to exa- 

 mine the question more attentively, and fortunately enabled 

 me to discover some new properties so interesting that I made 



• No reference is niade in these figures to the ])hiciiouicna which are 

 sct-ii by using bolii polurized light and tiic anulybing rlionib. 



