THE 
AMERICAN 
JOURNAL OF SCIENCE AND ARTS, 
[THIRD SERIES] 
Arr. XIL—Observations on Encke’s Comet at the Dartmouth 
College Observatory ; by Prof. C. A. Young. 
THE spectrum of this comet was observed on Dec. Ist, 2d, 
5th and 6th, and found to consist of three bright bands, of 
which the central one is by far the most conspicuous. The 
bands are pretty sharply defined at their lower (i. e., less refran- 
gible) edge, but fade gradually toward their upper limit. 
There was no indication of resolvability into lines, but the 
light was too feeble to allow the use of great dispersive power, 
or of a very narrow slit. I think that with the power and 
adjustment employed, no lines nearer to each other than Ji and 
bv could have been distinctly separate 
Yo continuous spectrum could be detected, nor any differ- 
ence, except in brightness, between the spectra of different por- 
ted the comet. as : 
fter trying several arrangements, with dispersive powers 
Tanging from ie to five eal it was found that the best 
In this instrument the eye-piece is provided with a b: 
crossing the center of the field of view parallel to the:slit, while 
the telescope itself can be moved by a tangent screw so as to 
bring any portion of the spectrum to the edge of the bar. 
There is also the ordinary scale viewed by reflection from the 
surface of the prism. ; 
The observations were made in the following manner: By 
Means of the tangent screw, the bar was so Pp aced as to hide 
Am, Jour, Sct.—Turrp Series, VoL. III, No. 14.—Fxs., 1872. 
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