328 CAPTAIN L. DARWIN, DR. A. SCHUSTER, AND MR. E. W. MAUNDER 
northern. It will be noticed from Mr. Wesley’s drawing that the side on which 
these lines appear is the side which was ricli in prominences. A similar phenomenon 
was shown in the photograph taken in 1882, when the hydrogen and calcium lines 
appeared strong in the corona on that side on which they were strong on the edge of 
the Sun, presumably in a prominence. 
The explanation which first suggests itself cannot be the true one. We might 
think that, if many prominences exist over one part of the Solar surface, the corona 
above, which undoubtedly does to some extent scatter the light falling on it, will 
show the prominence lines more strongly than other parts which have no pro¬ 
tuberances near them. No bright line could, however, be produced in this way, 
for the light scattered by the solid and liquid particles of the corona must have the 
same composition as the direct Sun light which reaches the Earth. The particles are 
illuminated not only by the prominence light, but by the light from the whole Solar 
surface beneath them. If we imagine ourselves placed near the Sun, the spectrum 
there seen cannot difier on the average from that which we observe here, and 
therefore the scattered light must also be of the same composition, and must show 
dark lines on a bright background, and not bright lines. 
Only one other explanation occurs to me. We must imagine that sufficient matter 
is actually thrown into the corona from the prominences to show the lines. This 
does not seem surprising if we look, for instance, at the lai’ge prominence on 
Mr. Wesley’s drawing. The life of such a prominence is short; had the eclipse 
taken place a few hours later, it might not have appeared as a prominence; but 
would it not have left behind it a sufficient quantity of calcium and hydrogen to 
show their characteristic lines ? We need only consider the remarkable effects 
produced in our atmosphere by the Krakatoa eruption, and reflect that matter is 
projected into the Solar atmosphere on a vastly larger scale, to see that the coronal 
spectrum, as we observe it, may contain injected calcium, which only very gradually 
sinks back again into the Sun. 
According to this view, we must separate the true coronal spectrum, which will be 
seen evenly all round the Sun, from the spectrum due to prominence matter, which 
will difier much in intensity during difterent eclipses. 
The strongest of the true corona lines has, according to my measurements, a wave¬ 
length 4232‘8. It is slightly less refrangible than the calcium line 4226'4 which 
forms a conspicuous feature in the Solar spectrum. That it is not identical with it is 
proved not only by the measurements, but by the fact that on the corona photograph 
the Fraunhofer line appears faintly by the side of the corona line. As the well 
known green corona line is always present in the spectrum of the chromosphere, it is 
very likely that this new line, which appears so strongly on our photographs, should 
frequently make its appearance there. Young, in his excellent book on “ The Sun,” 
gives, indeed, a line 4233'0 as one of about 30 lines which appear there on “very 
slight provocation.” It therefore seems highly probable that the two lines are 
identical, and that the comparatively weak Fraunhofer line 4233’0 is a corona line. 
