its having struck several observers independently. The
distinction of "cloud-prominences" from "flame-prominences" was
announced by Lockyer, April 27; by Zoellner, June 2; and by Respighi,
December 4, 1870.

The first description are tranquil and relatively permanent, sometimes
enduring without striking change for many days. Certain of the included
species mimic terrestrial cloud-scenery--now appearing like fleecy
cirrus transpenetrated with the red glow of sunset--now like prodigious
masses of cumulo-stratus hanging heavily above the horizon. The solar
clouds, however, have the peculiarity of possessing _stems_. Slender
columns can ordinarily be seen to connect the surface of the
chromosphere with its outlying portions. Hence the fantastic likeness to
forest scenery presented by the long ranges of fiery trunks and foliage
occasionally seeming to fringe the sun's limb. But while this mode of
structure suggests an actual outpouring of incandescent material,
certain facts require a different interpretation. At a distance, and
quite apart from the chromosphere, prominences have been perceived, both
by Secchi and Young, to _form_, just as clouds form in a clear sky,
condensation being replaced by ignition. Filaments were then thrown out
downward towards the chromosphere, and finally the usual appearance of a
"stemmed prominence" was assumed. Still more remarkable was an
observation made by Trouvelot at Harvard College Observatory, June 26,
1874.[603] A gigantic comma-shaped prominence, 82,000 miles high,
vanished from before his eyes by a withdrawal of light as sudden as the
passage of a flash of lightning. The same observer has frequently
witnessed a gradual illumination or gradual extinction of such objects,
testifying to changes in the thermal or electrical condition of matter
already _in situ_.

The first photograph of a prominence, as shown by the spectroscope in
daylight, was taken by Professor Young in 1870.[604] But neither his
method, nor that described by Dr. Braun in 1872,[605] had any practical
success. This was reserved to reward the efforts towards the same end of
Professor Hale. Begun at Harvard College in 1889,[606] they were
prosecuted soon afterwards at the Kenwood Observatory, Chicago. The
great difficulty was to extricate the coloured image of the gaseous
structure, spectroscopically visible at the sun's limb, from the
encompassing glare, a very little of which goes a long way in _fogging_
sensitive pl