260 
CAPTAIN W. DE W. ABNEY AND DR. A. SCHUSTER 
1878, may be taken as a type of what is seen at a time of few sun spots. We notice 
a great extension in two opposite directions. Unfortunately it has never been 
properly decided whether this direction agrees with the ecliptic or with the direction 
of the sun’s equator, or does not accurately agree with either. There is, however, a 
probability that the direction of greatest extension varies somewhat in different 
eclipses. This equatoreal extension (for we may so call it, without implying any 
hypothesis as to its cause) has, as a rule, a form which the Siamese in 1875 not 
inaptly likened to a fishtail, and for this reason the longest streamers of the corona 
are found not near the solar equator, but symmetrically at some distance from it. 
Another remarkable feature of the corona of the time of sunspot-minimum are the 
generally short and curved polar-rifts. They are found on all good drawings and 
photographs of the corona, when the eclipse took place at periods of small solar activity, 
and have often been compared to the rays of our aurora borealis. In our photographs 
we look in vain for the equatoreal extension and for the polar rifts. Streamers are seen 
to stretch away in all directions from the moon’s edge, but there is no regularity, 
whatever. The extent to which the corona can be traced in the photographs depends 
of course, on the time of exposure and the sensitiveness of the plates ; and considering 
the great progress which has lately been made in the science of photography, it is not, 
perhaps, astonishing, that our photographs show a greater extent of corona than any 
of those previously obtained. One of the streamers reaches, indeed, to a distance of 
44 minutes of arc from the sun’s limb, that is about 1'4 solar diameter. The details 
shown on the different photographs are very interesting, but they cannot be described, 
and are only shown on a good drawing. Two points, however, deserve a special notice.* 
One is the remarkable curvature of some of the coronal rays. It has long been known 
that these are not straight, but their general curvature shows more regularity than 
it did on the last occasion. The rays seem in many cases to start almost tangentially 
from the sun’s limb ; they are as a rule wider near the sun’s limb, and contract 
as their distance from the sun increases, while others are spread out in fan-like 
shape. The second point to which we wish to draw attention is the transparency of 
the streamers : in two instances at least we can trace structural details through the 
O 
luminous streamers. The distinction which has been drawn between the outer and 
the inner corona appears to us to be justified, the inner corona being decidedly more 
compact and luminous. The corona, as seen during this eclipse, does not seem to 
bring us any nearer to any plausible and scientific theory as to its causes. Two 
theories especially have been brought forward and discussed, and both of them seem 
to become less and less likely. The corona of last May is conclusive against any 
theory of meteor streams as far, at any rate, as its streamers are concerned, and the 
rival theory of a much disturbed solar atmosphere seems open to equally conclusive 
objections. It is only by means of continued observations that we may hope to solve 
the coronal mystery ; and these we are likely to have before long, thanks to Dr. 
Huggins’ important discovery. 
