Of the commoner phenomena attending an eclipse of the sun, as regards the appear ance of that luminary, nothing need be said; they are perfectly analogous to those of lunar E., except in the case of the eclipse being annular. There are other appearances, however, attending an eclipse of the sun, especially when it is total, that are very remarkable. The most instantaneous darkening of the orb of day, more particularly when it is unlooked for, is calculated to impress a spectator with vague terror; even when expected, it fills the mind with awe, as a demonstration of the forces and motions of the mechanism of the universe. The sudden darkness, too, is impressive from its strangeness as much as from occurring by day; it resembles neither the darkness of night nor the gloom of twilight. The cone of the moon's shadow, though it completely envelops the spectator, does not, as we have explained, inclose the whole atmosphere above his horizon. The mass of uninelosed air accordingly catches the sunlight, and reflects it into the region of the total eclipse, making there a peculiar twilight. Stars and planets appear, and all animals are dismayed by the dismal aspect of nature.—See Malioud•Bey's report of the total eclipse of July, 1860. Mr. Warren De la Rue, who was one of an expedition of scientific men who went to Spain to witness the same eclipse, gives the following account of the aspects of nature near the time of totality: `• When the sun was reduced to a small crescent, the shadows of all objects were depicted with great sharpness and blackness, reminding one of the effects of illumination with the electric light. The sky at this period assumed an indigo tint, and the landscape was tinged with a bronze hue."—Atkenceuin, 1860, vol. ii., page 259. At totality, there was still light enough to enable the observer to draw without the aid of his lamp, while the sky near the sun presented a deep and thence passed through a sepia tint to red and brilliant orange near the horizon. It mustbe said, however, that the strange appearance here recorded is exceptional, and probably not such as could ever occur in our latitude. There is one set of phenomena attending total E. of the sun, which are at once strange and invariable, and the causes of which cannot be said to be yet fully understood. As long as the total eclipse lasts, there appears round the sun and moon a luminous corona, while at its base, and projecting beyond the dark edge of the moon, appear very brilliant prominences, generally of a redcolor. These prominences were first observed during the total eclipse of 8th July, 1842; but they are found to be constant attendants on E., and methods have been invented of rendering them visible at any time without the interpo sition of the moon. The spectroscope reveals them to consist mainly of hydrogen gas in an incandescent state, and a comparatively narrow belt of the same color and substance runs round the whole circumference of the sun. The prominences are sometimes seen to shoot up like flames, in wild fantastic shapes, with incredible velocity, and to the: height of tens of thousands of miles.
In the eclipse of 1860 the light of the corona was a silvery white, and it extended beyond the moon's limb about eight tenths of her diameter. The corona consisted first of a bright ring of about 2' wide, and then an exterior and fainter ring of about 3', beyond which, for a mean distance of about 2', extended a glory of small rays—the whole corona extending to 7' beyond the moon's limb. From the corona, at intervals, projected individual rays of remarkable size, and five in number: one of 9' length; another of 14', and shaped like the point of a star; a third, sabre-shaped, and extending 28'•, a fourth, 28'; and a fifth, 10'. These individual rays are very differently described by different observers of the same eclipse, and are not well accounted for. The diffused light of the corona is believed to be caused by an immense extension of the gases form ing the red envelope, only in a cooler and rarer condition., 4. Prediction of Solar period of 18 Julian years 11 days, referred to in treating of the prediction of lunar E., applies equally to solar E. with lunar; but the ancients, who understood that fact, could find no law of recurrence of solar E. within that period, so as to predict them. The reason of the failure is obvious; for though solar E. recur in a fixed order within the cycle, they are not visible at the same places on their recurrence as when first observed. By modern methods, however, E. of the sun may be predicted, with all their circumstances of time and places of observation, with the most perfect certainty. We shall not, however, attempt to explain what these methods are; suffice it that they resemble those already generally described as applied in the case of lunar E. At the time of a solar eclipse, the sun and moon are in con junction; they are also in or near the same node; and no eclipse can happen if they are further than 17° from the node, or if the latitude of the moon, viewed from the earth, exceeds the sum of the apparent semi-diameters of the sun and moon. When within these limits, it is a problem of numbers and of spherical trigonometry to ascertain the nature of the eclipse, if any, which will happen.
The number of eclipses of the sun and moon together in a year cannot be less than two, or more than seven; the most usual number is four, and it is rare to have more than six. The explanation of the limitation of the number of E. is connected with the fact, that the sun passes by both nodes but once in a year, except in the case of his passing one early in the year, in which case, owing to the recession of the moon's nodes, he will again pass it a little before the end of the year. From the smallness of the cone of the moon's shadow, total solar E. are extremely unfrequent in any one place, compared with the frequency of their actual occurrence. At Paris there was only one total eclipse of the sun in the 18th c., that of 1724, and there will not be another till near the close of the 19th century. In London, not one total eclipse was witnessed during the 575 years, 1140-1715.