following chapter. The accompanying drawing (fig. 78) exhibits the prominences photographed by the American astronomers, the Moon's disc being reduced so as to permit all the prominences to be visible at once. The line FE indicates the course of the Moon's centre across the Sun, A B being a declination-circle, and C D The eclipse of August 7, 1869. From photographs by the a declination-parallel. The most successful photographing party was that headed by Dr. Mayer, at Burlington. But the two photographs by Dr. Curtis possess a special value on account of their delicacy and the number of details they exhibit. He has shown that the sharply-defined outlines of prominences, and even of the coronal glare, seen in most photographs of eclipses, result from excessive development. He proves satisfactorily, also, that the encroachment of the prominence-bases on the black disc of the Moon is due to a similar cause. In Dr. Curtis's contribution to Dr. Sand's elaborate report of the eclipse, the curious reader will find a very interesting investigation of the aspect of the prominence shown between E and c in fig. 78. He refers all its peculiarities of appearance to the action of a cyclonic storm in the upper regions of the solar atmosphere at this place. It remains only to be noticed that, even while this work has been passing through the printers' hands, Professor Young, of America, has succeeded in obtaining a photograph of a prominence when the Sun has been shining in full splendour. Although the result is, he tells us, not remarkable as a presentation of a solar prominence, yet as indicating the possibility of applying photography to record the condition of the chromosphere and prominences from day to day, from month to month, and from year to year, it is full of promise. The time seems not far off when we shall be as familiar with the laws according to which these mysterious objects appear, develope, and disappear within the solar atmospheric envelope, as we have already become with the general laws affecting the behaviour of Sun-spots. 313 CHAPTER VI. THE CORONA AND ZODIACAL LIGHT. THE coloured prominences, as we have seen, are phenomena which have been recognised only in recent times. We have now to deal with a phenomenon which has been known to astronomers for a much longer period, but has proved more difficult of interpretation, and remains even at the present day not clearly understood. It may fairly be believed that during the earliest total solar eclipses observed by mankind, the corona, or crown of glory, which surrounds the black disc of the Moon must have attracted attention. Yet the records of the recognition of this phenomenon are by no means so distinct as might have been expected. We do not find, indeed, in ancient works professedly treating of the phenomena of nature, any reference to the imposing appearance presented by the solar corona. The earliest allusion to the phenomenon is held by Professor Grant to be that passage in the Life of Apollonius' where Philostratus, speaking of the signs and wonders which occurred before the death of Domitian, says, 'In the heavens there appeared a prodigy of this nature; 6 a certain corona, resembling the Iris, surrounded the orb of the Sun, and obscured his light.' Taken alone, this passage would certainly not seem intended to describe the phenomena of a total eclipse; but as Philostratus afterwards remarks that the darkness was so great as to resemble night, we may assume with some confidence that a total solar eclipse had occurred. Plutarch more distinctly describes the appearance actually presented by the corona when he endeavours to explain why the darkness during a total eclipse is not so great as that of night. Even though the Moon,' he says, should hide at any time the whole of the Sun, still the eclipse is deficient in duration as well as amplitude, for a peculiar effulgence is seen around the circumference which does not allow a deep and very intense shadow.' I do not propose to record in full the observations which have been made upon the corona. To do so would occupy, indeed, much more space than can here be spared. Referring the reader who wishes for a more complete account of the earlier observations to Professor Grant's admirable History of the Physical Sciences,' I shall consider here those observations alone which tend to throw light on the nature of the corona. Some of the earlier observers of total solar eclipses would seem to have been misled by the great brightness of the corona close by the Sun, and to have supposed that a ring of direct sunlight had remained uncovered. We shall see presently that modern observers have also been struck with the brightness of the light close by the Sun; and it seems obvious that this bright light is to be regarded as wholly distinct from the light of the chromosphere, the redness of which is too marked to escape recognition. Remembering that before the invention of the telescope the corona was the only marked phenomenon to which observers were able to direct their attention, a certain weight attaches to their comments on the brightness near the Moon's disc. 6 Clavius having expressed his belief that the eclipse of 1567 was annular, Kepler was led to investigate the subject, and he proved that that eclipse must needs have been total. In 1605 he witnessed a total eclipse at Naples, and found, in the features it presented, the explanation of the remarks of Clavius. The whole body of the Sun,' he says, was completely covered for a short time, but around it there shone a brilliant light.' We might suppose that he referred to the chromosphere, because he says that the light was of a reddish hue;' but as he adds that it was ' of uniform breadth, and occupied a considerable part of the heavens,' there can be no doubt that he is speaking of the corona. Dr. Wyberd gives a remarkable account of the appearance of the corona during the total eclipse of March 29, 1652. When the Sun was reduced to a narrow crescent of light,' he says, 'the Moon all at once threw herself within the margin of the solar |