turbances is of too frequent occurrence to be accidental. M.
Trouvelot observed at Meudon, June 26, 1885, two active and evanescent
prominences thus situated, each rising to the enormous height of 300,000
miles; and on August 16, one scarcely less remarkable, balanced by an
antipodal spot-group.[559] It towered upward, as if by a process of
_unrolling_, to a quarter of a million of miles; after which, in two
minutes, the light died out of it; it had become completely extinct. The
development, again from the ends of a diameter, of a pair of similar
objects was watched, September 19 and 20, 1893, by Father Fenyi,
Director of the Kalocsa Observatory; and the phenomenon has been too
often repeated to be accidental.

The eclipse of August 29, 1886, was total during about four minutes over
tropical Atlantic regions; and an English expedition, led by Sir Norman
Lockyer, was accordingly despatched to Grenada in the West Indies, for
the purpose of using the opportunity it offered. But the rainy season
was just then at its height: clouds and squalls were the order of the
day; and the elaborately planned programme of observation could only in
part be carried through. Some good work, none the less, was done.
Professor Tacchini, who had been invited to accompany the party,
ascertained besides some significant facts about prominences. From a
comparison of their forms and sizes during and after the eclipse, it
appeared that only the growing vaporous cores of these objects are shown
by the spectroscope under ordinary circumstances; their upper sections,
giving a faint continuous spectrum, and composed of presumably cooler
materials, can only be seen when the veil of scattered light usually
drawn over them is removed by an eclipse. Thus all modestly tall
prominences have silvery summits; but all do not appear to possess the
"red heart of flame," by which alone they can be rendered perceptible to
daylight observation. Some prove to be ordinarily invisible, because
silvery throughout--"sheeted ghosts," as it were, met only in the dark.

Specimens of the class had been noted as far back as 1842, but Tacchini
first drew particular attention to them. The one observed by him in 1886
rose in a branching form to a height of 150,000 miles, and gave a
brilliantly continuous spectrum, with bright lines at H and K, but no
hydrogen-lines.[560] Hence the total invisibility of the object before
and after the eclipse. During the eclipse, it was seen fr