A Popular History of Astronomy During the Nineteenth Century: Fourth EditionClerke, Agnes M. (Agnes Mary)
History
A Popular History of Astronomy During the Nineteenth Century: Fourth Edition
Clerke, Agnes M. (Agnes Mary)
Astronomy -- History -- 19th century
No observations of importance were made during the eclipse of September
9, 1885. The path of total obscurity touched land only on the shores of
New Zealand, and two minutes was the outside limit of available time.
Hence local observers had the phenomenon to themselves; nor were they
even favoured by the weather in their efforts to make the most of it.
One striking appearance was, however, disclosed. It was that of two
"white" prominences of unusual brilliancy, shining like a pair of
electric lamps hung one at each end of a solar diameter, right above the
places of two large spots.[558] This coincidence of diametrically
opposite disturbances 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 Fényi,
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.
Public-domain text, read in full here on John Shaqi.
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