150 
MR. J. N. LOOKYER AND DR. SCHUSTER ON 
In some of the protuberances the lower edge does not seem to touch the body of 
the moon, but the gas seems to hang like clouds in the corona. 
Figs. 8 and 9, Plate 10, are copies of the photographs obtained by means of the 
prismatic camera. 
2. The Corona . 
We shall now have to examine the corona as shown on the photographs taken by 
the prismatic camera. If the spectrum given by the light of the corona is a line 
spectrum, we expect to find well-defined edges forming the limb of the moon. Only 
one such edge is seen on the photograph. It corresponds to the second ring of 
protuberances, and is, therefore, probably due to hydrogen. This was to be expected, 
as we know by the eye observations of Lockyer and Respighi that the hydrogen 
lines are the strongest lines in the photographic part of the corona. The upper part 
of the corona, as seen on the photographs, is such as would be given by homogeneous 
light, i.e. only one image of the corona is seen. We have tried several ways of 
finding the wave length of this fight. A circle of the size of the image of the moon 
was cut out of paper and put over the photograph until the corona was symmetrical 
round this circle, as we know it to have been symmetrical round the moon. When the 
circle was in this position its edge coincided with the Hy lower edge of the corona. 
The photograph of the corona was enlarged to the same size as the photograph of 
the prismatic camera. They were laid over each other so that the outlines of the 
corona coincided as well as possible. Here, again, it was found that the edge of the 
moon coincided with the Hy ring of protuberances. 
We think, therefore, that we are entitled to say that the photographic rays of the 
corona are chiefly due to the hydrogen fine Hy. Fig. 7, Plate 9, represents the 
protuberances and image of the corona symmetrical about the second series of 
protuberance as seen on our photograph. 
In addition to this fine spectrum of the corona, our photographs show strong marks 
of a continuous spectrum in its lower regions. This is chiefly shown by the well- 
defined structure running parallel to the fine of dispersion due to irregularities drawn 
out by the prism into bands. We can easily determine the limits of the continuous 
spectrum by examining them at the inner side of the photographs. On the one side 
the structure stops short at the hydrogen fine F. On the other edge, however, it 
extends to a considerable distance beyond the ultra-violet prominence line. Traces of 
fight are distinctly seen to a wave length of 3530 and beyond. 
Knowing the lim its of the continuous spectrum we can determine approximately the 
height to which it extends ; the distance between the extreme limit of the structure 
to the protuberance near H is about one and a half times the distance between the 
protuberance F and H. We know that we have no photographic trace beyond F, 
hence the angular height of the protuberance must be at least half the angular 
distance between the two prominences. The angular distance between the two pro- 
