nstrument adapted by its large aperture and short focus to give an
image of the utmost brilliancy. His observation, repeated during the
Caroline Island eclipse of 1883, was photographically verified ten years
later by M. de la Baume Pluvinel in Senegal.[532]

An instrument of great value for particular purposes was introduced into
eclipse-work in 1871. The "slitless spectroscope" consists simply of a
prism placed outside the object-glass of a telescope or the lens of a
camera, whereby the radiance encompassing the eclipsed sun is separated
into as many differently tinted rings as it contains different kinds of
light. These tinted rings were simultaneously viewed by Respighi at
Poodacottah, and by Lockyer at Baikul. Their photographic registration
by the latter in 1875 initiated the transformation of the slitless
spectroscope into the prismatic camera.[533] Meanwhile, the use of an
ordinary spectroscope by Herschel and Tennant at Dodabetta showed the
green ray of coronium to be just as bright in a rift as in the adjacent
streamer. The visible structure of the corona was thus seen to be
independent of the distribution of the gases which enter into its
composition.

By means, then, of the five great eclipses of 1860-71 it was
ascertained: first, that the prominences, and at least the lower part of
the corona, are genuine solar appurtenances; secondly, that the
prominences are composed of hydrogen and other gases in a state of
incandescence, and rise, as irregular outliers, from a continuous
envelope of the same materials, some thousands of miles in thickness;
thirdly, that the corona is of a highly complex constitution, being made
up in part of glowing vapours, in part of matter capable of reflecting
sunlight. We may now proceed to consider the results of subsequent
eclipses.

These have raised, and have helped to solve, some very curious
questions. Indeed, every carefully watched total eclipse of the sun
stimulates as well as appeases curiosity, and leaves a legacy of
outstanding doubt, continually, as time and inquiry go on, removed, but
continually replaced. It cannot be denied that the corona is a
perplexing phenomenon, and that it does not become less perplexing as we
know more about it. It presented itself under quite a new and strange
aspect on the occasion of the eclipse which visited the Western States
of North America, July 29, 1878. The conditions of observation were
peculiarly favourable. The weather was sup