several observers. Some of those stationed at Montpellier thought that the corona had a rotatory motion. Francis Baily compared the appearance of the corona to the flickering light of a gas illumination. Otto Struve, also, was much struck by the violent agitation to which, as it seemed to him, the light of the ring was subjected. The apparent extent of the corona as seen by different observers varied in a somewhat surprising manner. Otto Struve, observing at Lipesk, found the breadth of the corona equal to the Moon's apparent diameter; while M. Petit, observing at Montpellier, assigned to the corona a breadth scarcely exceeding one-fourth of this amount. Baily's estimate lay between these values. Nor were the observers in agreement as to the general appearance of the corona. Otto Struve observed several luminous expansions, some of them extending fully four degrees from the Moon's limb. Signor Picozzi, observing at Milan, saw two jets of light occupying a position which corresponded very nearly with that of the ecliptic. Several observers in France noticed a similar peculiarity. Minor rays, also, were distinctly recognised by Mauvais at Perpignan, and by Baily at Pavia. The last-named astronomer remarks, indeed, that the diverging rays were sufficiently marked to deprive the corona of the appearance of a ring. But Mr. Airy, observing the corona from the Superga, could scarcely recognise any radiation whatever; and he remarks, that although a slight radiation might have been perceptible, it was not sufficiently intense to affect in

a sensible degree the annular structure by which the luminous appearance was plainly distinguished.'

If we consider the accounts which the observers give of the brilliancy of the corona, we shall find that these peculiarities are in accordance with the theory that atmospheric conditions were alone in question. At the Superga the brightness of the corona seemed no greater than that of the Moon; but at Pavia, where Baily was stationed, the splendour of the corona was much greater. I had imagined,' this observer writes, that the corona, as to its brilliant or luminous appearance, would not be greater than that faint crepuscular light which sometimes takes place in a summer evening, and that it would encircle the Moon like a ring. I was therefore somewhat surprised and astonished at the splendid scene which now so suddenly burst upon my view.' We have seen that at Lipesk the corona seemed to extend much farther from the Sun than elsewhere, and accordingly we find that its brilliancy was also far greater. The light was so bright, Struve writes, that the naked eye could scarcely endure it. Many could not believe, indeed, that the eclipse was total, so strongly did the corona's light resemble direct sunlight.

But perhaps the most interesting and important observations made in 1842 are those which refer to the structure of the coronal light. It was noticed at Montpellier that the light of the corona was not uniform, nor merely marked with radiations, but that, in places, interlacing lines of light could be seen. Arago,

6

at Perpignan, recognised this peculiarity with the naked eye. He saw, a little to the left of a diameter passing through the highest point of the Moon's limb, a luminous spot composed of jets entwined in each other, and in appearance resembling a hank of thread in disorder.'

The accompanying picture (fig. 85) represents the

general phenomena seen during the eclipse of 1842; but it must be remembered, that such illustrations cannot be regarded as accurately representing details, because they are usually drawn after the eclipse is over, and represent merely what the observer remembers. Until the whole duration of a total eclipse is devoted by a skilful observer and draughtsman to the delineation of the corona, we cannot expect to have really trustworthy views.

During the eclipse of 1851 no observations were made which tended to throw new light on the nature of the corona. It is worthy of notice, however, that the Astronomer Royal found the aspect of the corona different from what he had noticed in 1842. The corona,' he says, 'was far broader than that which I saw in 1842. Roughly speaking, the breadth was little less than the Moon's diameter, but its outline was very irregular. I did not notice any beams projecting from it which deserved notice as much more conspicuous than the others; but the whole was beamy, radiated in structure, and terminated-though very indefinitelyin a way which reminded me of the ornament frequently placed round a mariner's compass. Its colour was white, or resembling that of Venus. I saw no flickering or unsteadiness of light. It was not separated from the Moon by any interval, nor had it any annular structure. It looked like a radiated luminous cloud behind the Moon.

These observations, combined with what had been before noticed, seem to demonstrate that the aspect of the corona is variable according to the circumstances under which it is viewed. It does not seem to be established that the rotatory and flickering motions suspected by other observers were only optical illusions, though the observation of the steadiness of the corona, by such an observer as the Astronomer Royal, goes far to negative observations of motion by less experienced astronomers. In the case of a phenomenon like the

corona, it is easier to imagine movement in the ring of light than to become convinced of its fixedness.

The eclipse of 1858, visible in Brazil, is chiefly remarkable on account of the strange drawing made by the French astronomer Liais (fig. 86). During the late eclipse (Dec. 1872), the accuracy of this singular picture was confirmed.

The eclipse of 1860 is remarkable as the first in

which the powers of photography were employed to aid in the resolution of the problems presented by the corona. It will be seen, on a reference to figs. 66 and 67, that Mr. De La Rue succeeded in obtaining traces of the corona. Those seen in Father Secchi's photographs are somewhat more distinct, the method he employed giving a smaller and more fully illuminated