The red prominences which appeared during the total eclipse of 1851 have been well described by the numerous skilled observers who proceeded to the countries of Northern Europe for the purpose of observing the phenomenon. According to Mr. Lassell, they were of a most brilliant lake colour, a splendid pink, quite defined and hard. Mr. Dawes remarked a bluntly triangular pink body suspended, as it were, in the corona, and the distance of which from the moon's limb was observed to increase as the moon continued to advance over the solar disc. The isolated patch of light was also seen by the greater number of the observers of the eclipse.
M. 3Ioesta, who observed the eclipse of 1853, remarked on the same side of the corona, with a very conspicuous protuberance, two darker spots, of a form approaching to a square, in apparent contact with the moon's limb. They seemed to indicate an interruption of the corona, or rather two apertures through which the dark ground of the heavens was visible. Their height above the moon's limb was estimated to amount to P.
The protuberances which appeared during the total eclipse of 1860 resembled in their general features those observed on previous occa sions. One of them appeared isolated from the moon's limb, but was seen to approach the latter as the moon advanced over the solar disk.
The question has been much discussed, whether the red prominences seen during a total eclipse of the sun belong to the sun or the moon. The observations of the total eclipse of I842 seemed to indicate that they are appendages of the sun, for it was remarked by several of the observers, that the protuberances on the western limb of the moon gradually increased in magnitude as the moon advanced over the solar disc, while those on the eastern limb similarly diminished in size, con sequences which would necessarily result from the protuberances being situate behind the dark body of the moon. This view of the origin of the protuberances was also strengthened by similar observations made during the eclipse of 1851 ; but it was established beyond all doubt by the observations of the eclipse of 1860. On the last-mentioned occasion it was remarked by several observers, that as the moon ad vanced over the solar disk, the protuberances on the eastern limb of the moon which first came into view, gradually diminished in size, while those on the western limb, which at the commencement of the totality were invisible, gradually increased in dimensions. This in teresting circumstance has also been indicated by photographs of the protuberances taken by Mr. Warren De La Rue, and by the Italian astronomer Professor Secchi.
Besides the protuberances which form so conspicuous an object during the totality of an eclipse, there has been generally observed at the parts of the moon's limb where the solar light disappears, and again at the parts where it reappears, a long red streak of light, appa rently of the same physical nature as the protuberances, and tending to support the opinion that the whole surface of the sun is enveloped in such a substance.
Attempts have been made to connect the rose-coloured protuberances with the solar spots, but the results of a careful comparison of the two classes of phenomena do not seem to indicate the existence of any physical relation between them. Other observers have endeavoured, but with no better success, to account for the protuberances by means of the faeuhe of the solar disk.
The most probable view of the nature of the more important phe nomena which reveal themselves during a total eclipse of the sun, is that the corona represents an atmosphere about the sun, and that the protuberances are emanations from a substance enveloping the surface of the sun, and somehow connected with the generation of the solar light and hest.
We shall conclude this article with adverting briefly to a phenomenon, apparently originating in an optical delusion, which has been sometimes remarked on the occasion of total or annular eclipses of the sun. In the case of an annular eclipse, the western limb of the moon, previous to the formation of the annulus, exhibits an indented appearance, resembling a succession of beads. Almost immediately the beads
become elongated, assuming the aspect of long black parallel streaks, uniting the limbs of the sun and moon. In the next instant these lines give way, as if they had been snapped asunder by the eastward motion of the moon, and the annulus then appears completely formed. The same succession of appearances has been witnessed when the eastern limb of the moon is approaching the corresponding limb of the sun. Phenomena of this nature were witnessed during the eclipses of 1724, 1737, 1748, and 1791. Nicolai also observed a similar appearance very distinctly during his observation of the annular eclipse of September 7, 1820, at Manheim. Ile remarked that about a second before the annulus was formed, the fine curve of the moon's disk, then in contact with the sun's limb, appeared broken into several parts ; and in a moment these parts flowed together like drops of water or quicksilver near each other. De Zach, who observed the same eclipse at Bologna, also remarks that before the contact of the two limbs was effected, there was visible, not a continuous thread of light, but a number of luminous points, resembling a row of so many pearl beads, separated by dark intervals. But the most vivid description of the phenomenon has been given by Francis Baily, who observed the annular eclipse of May 15, 1836, at Jedburgh, in the south of Scotland. (' Mem. Aat. Soc.,' voL x.) When the cusps of the sun, previous to the formation of the annulus, were about 40° asunder, a row of lucid points, like a string of beads, irregular in sizo and distance from each other, suddenly formed round the part of the circumference of the moon that was about to enter on the sun's disk. Its formation was so rapid that it presented the appearance of been caused by the ignition of a fine train of gunpowder. His impression was, that the annulus had just been formed, but to his great surprise he found that the luminous points, as well as the dark intervening spaces, increased in magnitude, some of the contiguous oues appearing to run into each other, like drops of water ; for the rapidity of the change was so great, and the singularity of the appearance so fascinating and attractive, that the mind was for the moment distracted, and lost in the contemplation of the scene, so as to be unable to attend to every minute occurrence. Finally, as the moon pursued her course, the dark intervening spaces (which at their origin had the appearance of lunar mountains in high relief, and which still continued attached to the sun's border) were stretched out into long, black, thick, parallel lines, joining the limbs of the sun and moon, when all at once they suddenly gave way, and left the circumference of the sun and moon in those points, as in the rest, comparatively smooth and circular ; and the moon perceptibly advanced on the face of the sun. The same appearance, although in a reverse order, was witnessed on the breaking up of the annulus. While the limb of the•moon was yet at some distance from the margin of the solar disk, a number of long, black, thick, parallel lines suddenly darted forward from the moon, and joined the two limbs as before. As these dark lines got shorter, the intervening bright parts assumed a more circular and irregular shape, and at length terminated in a fine curved line of bright beads, as at the commencement, till they ultimately vanished, and the annulus ceased to exist.
The'phenomenon alluded to in the foregoing description, which has received the appellation of " Baily's beads," has been carefully sought for on the occasion of all the total and annular eclipses which have been observed in recent times, but no confirmation of its existence has been obtained except in a few doubtful instances. The most probable explanation of its origin is that which supposes it to be due to some imperfection connected with the optical qualities of the telescope.