74; INVISIBLE LINES IN THE SUN'S SPECTRUM. [MJSMOIK HI. 



MEMOIR III. 



ON INVISIBLE FIXED LINES IN THE SUN's SPECTRUM DE- 

 TECTED BY PHOTOGRAPHY. 



From the Philosophical Magazine, May, 1843. 



CONTENTS: The photography of Fraunhofer* s fixed lines. The lines in 

 the red due to absorption by the earth's atmosphere. Nomenclature of 

 the Fraunhofer lines. Discovery of the invisible fixed lines. Origi- 

 nal map of them. The new ultra spectral red lines a, /3, y. Redis- 

 covered by Foucault and Fizeau. M. E. BecquereVs discovery. Ex- 

 periments in 1834. 



WHEN a beam of the sun's light, directed horizontally 

 by a heliostat, is admitted into a dark room, and, passing- 

 through a slit with parallel edges, is received on the sur- 

 face of a flint-glass prism, which retracts it at the angle 

 of minimum deviation, and, after its passage through the 

 prism, is converged to a focal image on a white screen 

 by the action of an achromatic lens, the resulting spec- 

 trum is given in great purity, and Fraunhofer's lines are 

 very distinct. If a photographic surface be set in the 

 place of the white screen, it will exhibit the representa- 

 tion of multitudes of dark lines, varying greatly in di- 

 mensions. 



After several attempts last summer, I succeeded in 

 discovering these lines, and have obtained impressions 

 of them sufficiently perfect. 



Before proceeding to the description of the mode to be 

 followed, and of the characters of the lines themselves, I 

 cannot avoid calling attention to the remarkable circum- 

 stance which has frequently presented itself to me of a 



