A. W. Wright—Spectrum of the Zodiacal Light. 45 
was pointed, and its position was found to be exactly the same, 
whether the light was derived from the zodiacal region, or 
directly from the aurora. On the other hand, the bright line 
was never seen when there was no aurora. 
It remains to consider the question whether there is a con- 
nection of any kind between the zodiacal light and the polar 
aurora. The considerations mentioned above do not absolutely 
exclude the possibility that, simultaneously with the aurora, 
and with a certain dependence upon it, some luminific pro- 
cess may be going on in space, which would cause the bright 
line to appear in the zodiacal spectrum, however improbable 
such a supposition ma . But if there were no better 
reason, the general invariability of the zodiacal light from 
night to night, and the constancy of its presence through- 
out all the months of the year, sufficiently indicate for it 
a different cause. Moreover, on at least two of the evenings 
when only a continuous spectrum was seen, there was an 
aurora, moderately bright, though not extending to any great 
distance from the horizon. If the two were in an y way related, 
we should expect some variation in the zodiacal light coinci- 
dent with the appearance of remarkable auroral displays, but 
it does not appear that any such thing has ever been observed. 
There seems to be no evidence that they are not entirely inde- 
pendent phenomen. 
ne or two additional observations may be mentioned here 
as of interest. On several oceasions when the slit of the spec- 
troscope had a breadth of only two or three divisions, the 
spectrum at the first glance appeared to end suddenly at about 
5+ of the seale. Further examination showed light beyond, 
and that the apparent abruptness of its termination was caused 
by a dark band of about the width of the slit, which was found 
to occupy, as nearly as could be estimated, the exact position 
of the band marked 6 in the plate. It is doubtless identical 
with it, and caused by aah absorption. eee 
1€ spectrum on the most favorable nights was still visible 
when the slit was narrowed to one division of the scale, and on 
one occasion the opening was reduced to 0°6 of a division. that 
is, to an actual breadth of 0:073™ before the light became 
imperceptible. As the prneipal Fraunhofer lines are distinctly 
described, in 
lower latitudes, where the intensity of the light is known to be 
much greater. 
