e earth
produces what we call a total eclipse. The few minutes during which a
total eclipse lasts are of much interest to the astronomer. Darkness
reigns over the landscape, and in that darkness rare and beautiful
sights are witnessed.

[Illustration: Fig. 19.--Prominences seen in Total Eclipse.]

We have in Fig. 19 a diagram of a total eclipse, showing some of the
remarkable objects known as prominences (_a_, _b_, _c_, _d_, _e_) which
project from behind the dark body of the moon. That they do not belong
to the moon, but are solar appendages of some sort, is easily
demonstrated. They first appear on the eastern limb at the commencement
of totality. Those first seen are gradually more or less covered by the
advancing moon, while others peep out behind the western limb of the
moon, until totality is over and the sunlight bursts out again, when
they all instantly vanish.

The first total eclipse which occurred after the spectroscope had been
placed in the hands of astronomers was in 1868. On the 18th August in
that year a total eclipse was visible in India. Several observers, armed
with spectroscopes, were on the look-out for the prominences, and were
able to announce that their spectrum consisted of detached bright lines,
thus demonstrating that these objects were masses of glowing gas. On the
following day the illustrious astronomer, Janssen, one of the observers
of the eclipse, succeeded in seeing the lines in full sunlight, as he
now knew exactly where to look for them. Many months before the eclipse
Sir Norman Lockyer had been preparing to search for the prominences, as
he expected them to yield a line spectrum which would be readily
visible, if only the sun's ordinary light could be sufficiently winnowed
away. He proposed to effect this by using a spectroscope of great
dispersion, which would spread out the continuous spectrum considerably
and make it fainter. The effect of the great dispersion on the isolated
bright lines he expected to see would be only to widen the intervals
between them without interfering with their brightness. The new
spectroscope, which he ordered to be constructed for this purpose, was
not completed until some weeks after the eclipse was over, though before
the news of Janssen's achievement reached Europe from India. When that
news did arrive Sir N. Lockyer had already found the spectrum of unseen
prominences at the sun's limb. The honour of the practical application
of a method of observ