minutes the clouds broke, and across the driving wrack a "long,
finger-like projection" jutted out over the margin of the dark lunar
globe. In another moment the spectroscope was pointed towards it; three
bright lines--red, orange, and blue--flashed out, and the problem was
solved.[514] The problem was solved in this general sense, that the
composition out of glowing vapours of the objects infelicitously termed
"protuberances" or "prominences" was no longer doubtful; although
further inquiry was needed for the determination of the particular
species to which those vapours belonged.

Similar, but more complete observations were made, with less atmospheric
hindrance, by Tennant and Janssen at Guntoor, by Pogson at Masulipatam,
and by Rayet at Wha-Tonne, on the coast of the Malay peninsula, the last
observer counting as many as nine bright lines.[515] Among them it was
not difficult to recognise the characteristic light of hydrogen; and it
was generally, though over-hastily, assumed that the orange ray matched
the luminous emissions of sodium. But fuller opportunities were at hand.

The eclipse of 1868 is chiefly memorable for having taught astronomers
to do without eclipses, so far, at least, as one particular branch of
solar inquiry is concerned. Inspired by the beauty and brilliancy of the
variously tinted prominence-lines revealed to him by the spectroscope,
Janssen exclaimed to those about him, "Je verrai ces lignes-la en dehors
des eclipses!" On the following morning he carried into execution the
plan which formed itself in his brain while the phenomenon which
suggested it was still before his eyes. It rests upon an easily
intelligible principle.

The glare of our own atmosphere alone hides the appendages of the sun
from our daily view. To a spectator on an airless planet, the central
globe would appear attended by all its splendid retinue of crimson
prominences, silvery corona, and far-spreading zodiacal light projected
on the star-spangled black background of an absolutely unilluminated
sky. Now the spectroscope offers the means of indefinitely weakening
atmospheric glare by diffusing a constant amount of it over an area
widened _ad libitum_. But monochromatic or "bright-line" light is, by
its nature, incapable of being so diffused. It can, of course, be
_deviated_ by refraction to any extent desired; but it always remains
equally concentrated, in whatever direction it may be thrown. Hence,
when it is mixed up wi