OF AETS A3s"D SCIENCES. 279 



XXII. 



ON PHOTOGRAPHS OF THE SOLAR SPECTRUM. 



Br Robert Amokt, M.D. 



Read, May 10, 1876. 



In continuation of the experiments first presented to the Academy 

 a year ago concerning the photography of absorption bands fi'om liglit 

 transmitted through colored solutions, I take pleasure in announcing, 

 that owing in great part to the assiduous application of my assistant, 

 Mr. J. H. Hubbard, the lines between F and D of the solar spectrum 

 have been distinctly impressed upon a sensitized collodion plate. The 

 plate I now present to the Academy shows these lines unmistakably, 

 the double line of D being perfectly visible. The image is impressed 

 upon that kind of collodion which is coated upon what are known as 

 the " Stuart -Wortley Plates." 



I believe this is the first time that a sharp photographic image of 

 the D line has ever been exhibited ; though 1 am well aware that 

 others have reported that they have been able to obtain photographic 

 effects from the yellow and red rays of the spectrum. 



You are probably aware that these are dried plates ; and in addi- 

 tion to the advantage of using a dry plate, in which the decomposi- 

 tion may be su^jposed to continue more favorably than on a wet plate, 

 which is constantly drying up when exposed, mention may be made of 

 the probable ingredients used in the dry process. These consist of 

 bromide of silver, salicine, and uranium, among others ; and it was evi- 

 dent to us, from certain of our preliminary experiments, that the 

 glucosides, added to collodion, increased the sensitiveness of the plates 

 exposed to the green rays. Hence we were induced to use these in 

 preference to the ordinary dry tannin plates. An exposure of thirty 

 to forty-five minutes is required in order to obtain a distinct image of 

 the solar lines in that portion of the spectrum which I have here pre- 

 sented. 



You will observe that the image is brought to a principal focus in the 

 vicinity of E and b lines ; in fact, that eight of the group of E lines are 



