OF ARTS AND SCIENCES. 



223 



I>;vESTiOATioxs ON LiGHT AND IIeat, made and published wholly or in part with appropriation 

 from the Rumford Fond. 



X. 



ON THE PHOSPHOROGRAPH OF A SOLAR SPECTRUM, 

 AND ON THE LINES IN ITS INFRA-RED REGION. 



By John William Draper, M.D. 



Professor of Chemistry in the University of New York. 



I PROPOSE in this communication to consider: 1. The peculiarities 

 of a 25hosphorograph of the solar spectrum as compared with a photo- 

 Ejraph of the same object ; 2. The antagonization of effect of rays of 

 higher by those of lower refrangibility. 



There is a striking resemblance between a photograph of that spec- 

 trum taken on iodide of silver and a phosphorograph taken on lumi- 

 nous paint, and other phosphorescent preparations. There are also 

 differences. 



I. Description op the Photographic Spectrum. 



In 1842, I obtained some very fine impressions of the first kind 

 (on iodide of silver), and described them in the " Philosophical Maga- 

 zine" (November, 1842), and again in February, 1847. One of these 

 was made the subject of an elaborate examination by Sir J. Herschel. 

 His description and explanatory views of it may be found in that 

 journal, February, 1843. 



From these it appears that such a photograph, taken in presence of 

 a weak extraneous light, may be considered as presenting three regions. 

 1. A middle one extending from the boundary of the blue and green 

 to a little beyond the violet ; in this region the argentic iodide is 

 blackened. 2. Below this, and extending from the boundary of the 

 blue and green to the inferior theoretical limit of the prismatic spec- 

 trum^ is a region strongly marked in which the action of the daylight 

 has been altogether arrested or removed, the daylight and the sunlight 

 having apparently counterbalanced and checked each other. 3. A 

 similar protected region occurs beyond the violet. This, however, 

 is very much shorter than the preceding. The sketch annexed to 

 Herschel's paper represents these facts as well as they can be by an 

 uncolored drawing. 



