AMERICAN 
JOURNAL OF SCIENCE AND ARTS, 
[THIRD SERIES] 
—_— 
Art. XLIV.—On Diffraction Spectrum Photography; by HENRY 
Draper, M.D., Professor of Analytical Chemistry and Physi- 
ology in the University of New York. (Illustrated by a pho- 
tograph printed by the Alberttype process.) 
THERE are, as is well known, two methods by which spectra 
may be obtained : Ist, by the action of a prism; 2d, 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 spec- 
trum as an interference or diffraction spectrum. A casual in- 
‘pection shows that there is a great difference between the spec- 
tra produced by these two methods, and close investigation 
ashi that the diffraction spectrum is by far the more suitable 
°r accurate scientific work. For this reason it has seemed de- 
sirable to make a trustworthy map of those pe of the solar 
diffraction spectrum which can be photographed on collodion, 
a to attach to it a scale for reading the wave-lengths of the 
$ 
The plate accompanying this memoir is from collodion pho- 
Eaphs made by myself, transferred to a thick piece of glass, the 
tter process being known as the Alberttype. For the entire 
tecess of this transfer I am indebted to my friend Mr. E. Bier- 
_the owner of the patent in America. The glass is then 
used in a printing press in the same manner as a lithographic 
— The spectrum is absolutely unretouched. It represents 
*refore the work of the sun itse f, and is not a drawing either 
made oy Corrected by hand. : 
.u€ picture consists of two portions; Ist, the upper, which 
S!ves all the lines of the spectrum from near G to Q, or from 
- Jour, Scr.—Tuep — Vou. VI, No. 36,—Dgc., 1873. 
