Herbert H. Turner and Simon Newcomb

“ Hansen’s method differs from that of Bessel in that the ecliptic is taken as the fundamental plane instead of the equator. The axis of X on the fundamental plane is parallel to the plane of the ecliptic; that of Y perpendicular to it. The other elements are nearly the same in the two theories. As to their relative advantages, it may be remarked that Hansen’s co-ordinates follow most simply from the data of the tables, and are necessarily used in eclipse tables, but that the subsequent computation is simpler by Bessel’s method. ”

“ The most extended streamers are very little brighter than the sky, and must be photographed with long exposures.
The first application of the spectroscope to the phenomenon was made during the total solar eclipse of August 18, 1868, by P. J. C. Janssen and other observers in India. By them was made the capital discovery that the red solar prominences give a spectrum of bright lines, and are therefore immense masses of incandescent gases, chiefly hydrogen and the vapours of calcium and helium. ”

“ It is possible that two lines observed by Young in 1869, namely, W. L. (Ångstrom) 5450 and 5570, should be added to the list of undoubted coronal lines. It is not likely that helium or hydrogen or calcium vapour forms part of the corona. The wave-lengths of some 700 lines belonging to the chromosphere and prominences were determined by the British parties.
The eclipse of August 9, 1896, was total in Norway, Novaya Zemlya and Japan. ”

“ The subject is one demanding further observation. High prominences are generally “white” at their summits, “red” at their bases. The Harvard College Observatory photographs show the corona out to 90′ from the moon’s limb, though no detail is visible beyond 60′. W. H. Pickering made a series of photographic photometric measures of the corona, some of which are given below, together with results deduced by Holden from the eclipses of January and December 1889:—
The results in the first and third columns are derived from plates taken in a very humid climate, and are not very different. ”

“ Of these, Oppolzer’s are constructed with greater numerical accuracy and detail, while Newcomb’s are founded on more recent astronomical data, and are preferable for computing ancient eclipses. F. K. Ginzel’s Spezieller Kanon der Sonnen- und Mondfinsternisse (Berlin, 1899) contains, besides the historical researches already mentioned, maps of the paths of central eclipses visible in the lands of classical antiquity from 900 B.C. to A.D. 500, but computed with imperfect astronomical data. ”

“ These conditions being understood, the cycles of recurrence of eclipses of either kind can be worked out geometrically from the mean motions of the sun, moon, node and perigee by the aid of geometric conceptions shown in their simplest form in fig. ”