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
Thus, first-fruits of accurate knowledge regarding the solar
surroundings were gathered, while the value of the brief moments of
eclipse gained indefinite increase, by supplementing transient visual
impressions with the faithful and lasting records of the camera.
In the year 1868 the history of eclipse spectroscopy virtually began, as
that of eclipse photography in 1860; that is to say, the respective
methods then first gave definite results. On the 18th of August, 1868,
the Indian and Malayan peninsulas were traversed by a lunar shadow
producing total obscuration during five minutes and thirty-eight
seconds. Two English and two French expeditions were despatched to the
distant regions favoured by an event so propitious to the advance of
knowledge, chiefly to obtain the verdict of the prism as to the
composition of prominences. Nor were they despatched in vain. An
identical discovery was made by nearly all the observers. At Jamkandi,
in the Western Ghauts, where Lieutenant (now Colonel) Herschel was
posted, unremitting bad weather threatened to baffle his eager
expectations; but during the lapse of the critical five and a half
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-là en dehors
des éclipses!" 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.
Public-domain text, read in full here on John Shaqi.
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