AMERICAN JOURNAL OF SCIENCE. 
[THIRD SERIES.] 
Art. XXXV.—On Photographs of the Spectrum of the Nebula 
4 D.* 
in Orion; by HENRY DRAPER, M. 
similar series; and second, to photograph the spectrum of the 
Nebula in various parts so as to see whether any new lines 
could be found, and also whether the composition is uniform 
throughout. 
As to the first of these objects I have recently succeeded in 
taking a very fine and extensive photograph of the Nebula 
containing most of the delicate outlying parts which were not 
in my earlier photographs. This is in the hands of the photo- 
lithographer now and will shortly be published. The experi- 
ments have been very difficult because an exposure of more 
than two hours in the telescope has been necessary, and an. 
exceedingly minute motion of the stars relative to the sensi- 
tive plate will become apparent on account of the high magni- 
fying power (180), employed. te 
n carrying out the second object two contrivances have 
been used ; first, a direct vision prism in the cone of rays from 
the objective before they had reached a focus, and second the 
two-prism spectroscope with which I have taken photographs 
of stellar spectra for some years past. 
* Read before the National Academy of Sciences, April, 1882, at Washington. 
Am. Jour. en doa Series, Vo.. XXIII, No. 137.—May, 1882. 
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