374 OC. A. Young—Spectrum of Brorsen’s Comet. 
of the micrometer-screw and by the reading of the scale, illu- 
minated for a moment after the bar has been set. 
On April 1st I got three scale readings—respectively 99°9, 
100-0 and 100-4, the value of one scale division in this part of 
the spectrum being very nearly 25 units of Angstrém’s scale, 
or about double the distance between the extreme lines of the 
b group, the readings decreasing with the wave length. 
Just before dark 6, in the spectrum of daylight coincided 
with 100 on the scale; also, immediately after the third point- 
ing and without disturbing the telescope, spectroscope, or 
micrometer, the flame of a Bunsen burner was presented to the 
slit, and the lower edge of the green band in the well-known 
spectrum of this flame was found to show itself at the edge of 
the occulting bar precisely where the comet spectrum had 
een. We may therefore fairly conclude that the lower edge 
of the central band in the comet spectrum had a wave length 
of very nearly 517 millionths of a millimeter. The observa- 
tion of April 8d confirms this, though but a single reading 
could be obtained. The only special interest in this observa- 
tion lies in the fact that in 1868 Mr. Huggins obtained a some- 
what different result for this same comet. 
n an elaborate paper published some years ago by Vogel in 
Poggendorff’s Annalen upon the spectra of comets, he comes 
to the conclusion that there are several different kinds of com- 
etary spectra, the differences lying merely in the wave-length 
of the bands. But he seems to have reached this conclusion 
by oe rather too high a degree of accuracy to the obser- 
vations. ith the exception of Brorsen’s comet, it wou 
It would now appear from my observations that Brorsen’s 
comet also must fall into line with the rest. 
every precaution would seem to have been taken. 
However this may be, I am quite positive as to the accuracy 
trum. 
The comet is moving very nearly in the path assigned oy 
_ the ephemeris of Schulze. It is easily visible in the 3-ine 
