T H E 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



DECEMBER 1873. 



LIV. On Diffraction- Spectrum Photography. By Henry Dra- 

 per, M.D. f Professor of Analytical Chemistry and Physio- 

 logy in the University of New York*. 



[Illustrated by a Photograph (Plate IV.) printed by the Alberttype 

 process.] 



THERE are, as is well known, two methods by which spectra 

 may be obtained : — 1st, by the action of a prism ; 2nd, by a 

 system of closely ruled lines. In the latter case it is convenient 

 to speak of the contrivance employed as a grating, and of the 

 spectrum as an interference- or diffraction-spectrum. A casual 

 inspection shows that there is a great difference between the 

 spectra produced by these two methods ; and close investigation 

 proves that the diffraction -spectrum is by far the more suitable 

 for accurate scientific work. For this reason it has seemed de- 

 sirable to make a trustworthy map of those parts of the diffrac- 

 tion-spectrum which can be photographed on collodion, and to 

 attach to it a scale for reading the wave-lengths of the rays. 



The Plate (PI. IV.) accompanying this memoir is from collodion 

 photographs made by myself, transferred to a thick plate of glass, 

 the latter process being known as the Alberttype. For the entire 

 success of this transfer I am indebted to my friend Mr. E. Bier- 

 stadt, the owner of the patent in America. The glass is then 

 used in a printing-press ia the same manner as a lithographic 

 stone. The picture is absolutely unretouched. It represents, 

 therefore, the work of the sun itself, and is not a drawing either 

 made or corrected by hand. 



It consists of two portions — first, the upper, which gives all 



* Communicated by the Author, to whom we are also much indebted 

 for the impressions of the beautiful photograph. 



Phil. Mag. S. 4. Vol. 46. No. 308. Dec. 1873. 2 F 



