of unusual excellence.
Their comparison and study placed it beyond reasonable doubt that the
radiated corona belonging to periods of maximum sun-spots gives place,
at periods of minimum, to the "winged" type of 1878. Professor Holden
perceived further that the equatorial extensions characterising the
latter tend to assume a "trumpet-shape."[563] Their extremities diverge,
as if mutually repellent, instead of flowing together along a medial
plane. The maximum actinic brilliancy of the corona of January 1, 1889,
was determined at Lick to be twenty-one times less than that of the full
moon.[564] Its colour was described as "of an intense luminous silver,
with a bluish tinge, similar to the light of an electric arc."[565] Its
spectrum was comparatively simple. Very few bright lines besides those
of hydrogen and coronium, and apparently no dark ones, stood out from
the prismatic background.

"The marked structural features of the corona, as presented by the
negatives" taken by Professors Nipher and Charroppin, were the filaments
and the streamers. The filaments issued from polar calottes of 20 deg.
radius.

"The impression conveyed to the eye," Professor Pritchett wrote,[566]
"is that the equatorial stream of denser coronal matter extends across
and through the filaments, simply obscuring them by its greater
brightness. The effect is just as if the equatorial belt were superposed
upon, or passed through, the filamentary structure. There is nothing in
the photographs to prove that the filaments do not exist all round the
sun.[567] The testimony from negatives of different lengths of exposure
goes to show that the equatorial streamers are made up of numerous
interlacing parts inclined at varying angles to the sun's equator."

The coronal extensions, perceptible with the naked eye to a distance of
more than 3 deg. from the sun, appeared barely one-third of that length
on the best negatives. Little more could be seen of them either in
Barnard's exquisite miniature pictures, or in the photographs obtained
by W. H. Pickering with a thirteen-inch refractor--the largest
instrument so far used in eclipse-photography.

The total eclipse of December 22, 1889, held out a prospect,
unfortunately not realized, of removing some of the doubts and
difficulties that impeded the progress of coronal photography.[568]
Messrs. Burnham and Schaeberle secured at Cayenne some excellent
impressions, showing enough of the corona to prove its ident