see also the accompanying photographs.]

CHAPTER III

_RECENT SOLAR ECLIPSES_

By observations made during a series of five remarkable eclipses,
comprised within a period of eleven years, knowledge of the solar
surroundings was advanced nearly to its present stage. Each of these
events brought with it a fresh disclosure of a definite and unmistakable
character. We will now briefly review this orderly sequence of
discovery.

Photography was first systematically applied to solve the problems
presented by the eclipsed sun, July 18, 1860. It is true that a
daguerreotype,[512] taken by Berkowski with the Koenigsberg heliometer
during the eclipse of 1851, is still valuable as a record of the corona
of that year; and some subsequent attempts were made to register partial
phases of solar occultation, notably by Professor Bartlett at West Point
in 1854;[513] but the ground remained practically unbroken until 1860.

In that year the track of totality crossed Spain, and thither,
accordingly, Warren de la Rue transported his photo-heliograph, and
Father Secchi his six-inch Cauchoix refractor. The question then
primarily at issue was that relating to the nature of the red
protuberances. Although, as already stated, the evidence collected in
1851 gave a reasonable certainty of their connection with the sun,
objectors were not silenced; and when the side of incredulity was
supported by so considerable an authority as M. Faye, it was impossible
to treat it with contempt. Two crucial tests were available. If it could
be shown that the fantastic shapes suspended above the edge of the dark
moon were seen under an identical aspect from two distant stations, that
fact alone would annihilate the theory of optical illusion or "mirage";
while the certainty that they were progressively concealed by the
advancing moon on one side, and uncovered on the other, would
effectually detach them from dependence on our satellite, and establish
them as solar appendages.

Now both these tests were eminently capable of being applied by
photography. But the difficulty arose that nothing was known as to the
chemical power of the rosy prominence-light, while everything depended
on its right estimation. A shot had to be fired, as it were, in the
dark. It was a matter of some surprise, and of no small congratulation,
that, in both cases, the shot took effect.

De la Rue occupied a station