distance of 900,000 miles, or more than 2,000,000 miles from the imagined limits of this zodiacal matter, the shadow would end in a point. Nor would the penumbra extend far enough to hide any but a relatively small portion of the supposed matter. It is hardly necessary to point out that no such phenomenon has ever been witnessed either in the winter months or at any other season. So that, independently of a host of other objections, this one-rightly understood-disposes of Oudemann's theory, and of all others which require that matter admitting of being rendered visible to us by the sun's light exists at the moon's distance.

Yet these radial beams remain to be explained, for I think few will be disposed to assert that they are due to mere optical illusion.*

I believe that the chief interest of the eclipse observations is not unlikely to be associated with the interpretation of the coronal radiations. For, as it seems to me, the difficulty of interpreting them is altogether greater than that of explaining the corona itself. As respects this last, indeed, it seems to me improbable that the evidence we have can be made much fuller or more convincing than it is at present. But as respects the beams we have much to learn before it would be safe to hazard an opinion. Nor is it by any means unlikely that we may find in these beams a problem as difficult of solution as that presented by the phenomena of comets.

It will be well to consider some of the accounts which have been given of the coronal beams. More particularly it will be interesting to inquire whether we have satisfactory evidence as to their fixity during the whole continuance of totality. For though their appearing to change in position would afford us very satisfactory evidence as to their nature, their immobility, if it could be established, would have great significance.

It is worthy of notice, at the outset, that accounts referring to apparent motion are less likely to be trustworthy than those which distinctly state that the beams remain fixed in position. For, in the first place, an inexperienced observer might very well be misled into the supposition that a radiated glory of light had a certain degree of motion; and in the

* Oudemann accepts somewhat confidently Dr. Gould's statement that the coronal beams changed in position during the American eclipse. Dr. Curtis remarks however, and the study of the various narratives fully confirms the assertion, that all the other observers describe the rays as fixed in position. I do not know that their apparent movement, if confirmed, could be regarded as demonstrating anything as to their nature; but in this, as in other cases, all the best authenticated accounts speak of them as remaining unchanged.

second, the shifting lights around the horizon, as the shadow sweeps across the station of the observer, would tend greatly to encourage the illusion. To this may be added the circumstance that at the first formation of the corona, and as it is disappearing, an apparent rotational movement results from the rapid closing in and separation of the solar cusps. I find that the accounts of apparent motion in the coronal beams are few in number and of little weight compared with those which assert the fixity of the rays; and I cannot recall any instance in which an observer speaks of the apparent motion as of a phenomenon he had been at the pains to convince himself of, whereas those who refer to the fixity of the beams speak sometimes very definitely on this point.

Here are a few accounts of apparent motion.

Don Antonio d'Ulloa, speaking of the eclipse of 1778, says, "the corona seemed to be endued with a rapid rotatory motion, which caused it to resemble a firework turning round its centre." But it does not seem at all clear that he refers to the beams, because he says, "there appeared issuing from the corona a great number of rays of unequal length, which could be discerned to a distance equal to the lunar diameter." This "discerning" of the rays seems to imply that they were unmoved; and certainly the observation would prove too much if it were accepted as establishing a sort of Catherine-wheel motion of the radial beams.

In 1842 several observers, says Grant, "asserted that the ring of light" (not the rays) "turned continually round its centre." "At Lipetsk," he adds, "the light of the ring seemed to M. Otto Struve to be in a state of violent agitation." Then follows the best testimony yet given in favour of apparent changes in the beams. "Mr. Baily states," says Professor Grant, "that the rays had a flickering appearance, somewhat like that which a gas-illumination might be supposed to assume if formed into a similar shape." It will be admitted, however, that there is here no convincing evidence of a change of place in the beams, and further that the changes of brightness are fairly comparable with those flickerings which Chladni, Encke, Humboldt, Bessel, and other astronomers have noted in the case of comets, and which have even at times been noticed in the zodiacal light. When we remember that the coronal beams are necessarily seen through our atmosphere, which mustundergo very important changes of temperature during the continuance of totality, and probably be subject to waves of disturbance, we cannot wonder that the illumination of these delicate objects should seem fitful.

Now when we turn to narratives describing the fixity of the coronal beams, we find much more satisfactory evidence.

In the carefully observed eclipse of 1733, M. Edstrom, mathematical lecturer in the Academy of Charlestadt, noted "that the ring appeared everywhere of equal breadth, save where it emitted rays from above as well as from below; that these rays were equal in brilliancy, but unequal in length; and that they plainly maintained the same position, until they vanished along with the ring upon the appearance of the sun's limb." I take this account from Professor Grant's admirable "Physical History of Astronomy;" and the italics are his. The same eclipse afforded abundant evidence of the extreme delicacy of the light of these radiations, for "at Lincopia," says Grant, "the ring appeared of a bright white colour, but it did not exhibit a radial aspect."

Bruhns, of Leipsic, speaks thus of the appearance of a long radial beam seen during the eclipse of 1860: "On the eastern side a long ray shot out to a distance of about a degree; at the base its breadth was three minutes, but it tapered down to about a minute and a half in breadth near its extremity. During the ten seconds that my attention was directed to it, neither the direction nor the length of the ray altered. Its light was fainter than that of the corona, which was brilliantly white and seemed to twinkle."

I have already remarked that all the observers of the American eclipse of last year, save Dr. Gould alone, speak of the fixity of the beams. The following instances may be specially cited. Professor Simon Newcombe says: "Looking directly at the corona, there was no actual appearance of striation, but it seemed to be of a jagged outline, extending out into four sharp points nearly in the horizontal and vertical direction, while between these points the serrated edge hardly seemed to extend beyond the body of the moon. The greatest distance to which the extreme points seemed to extend did not exceed a semi-diameter of the moon, and there was nothing like long rays of light extending out in any direction whatever. When I turned my head the points did not seem to turn with it. Still I experienced a singular difficulty in judging accurately either of the number or direction of the jagged points, or of the extent to which they might be optical illusions produced by the differences in the height and brilliancy of different parts of the corona. . . . Seen through a green glass, the corona consisted simply of four or five prominences, extending around the moon, smooth in their outline, shading off by imperceptible gradations, and rising to different heights."

General Myer, by observing the eclipse from the summit of White Top Mountain, obtained a far better view of the radial beams than any of the observers at lower levels. a centre," he says, "there stood the full and intensely black

"As

disc of the moon, surrounded by the aureola of a soft, bright light, through which shot out, as if from the circumference of the moon, straight, massive, silvery rays, seeming distinct and separate from each other, to a distance of two or three diameters of the lunar disc, the whole spectacle showing as upon a background of diffused rose-coloured light. . . . The silvery rays were longest and most prominent at four points of the circumference, two upon the upper and two upon the lower portion, apparently equidistant from each other, giving the spectacle a quadrilateral shape. The angles of the quadrangle were about opposite the north-eastern, north-western, southeastern, and south-western points of the compass. . . . There was no motion of the rays.'

The spectroscope may perhaps afford some information respecting the structure of these beams; but the faintness of their light will render spectroscopic observation very difficult. If I were willing to hazard a speculation as to their structure and physical cause, I should associate them, I think, with the tails of comets, and regard them as phenomena indicating the action of some repulsive force exerted by the sun. Sir John Herschel has pointed out that we have demonstrative evidence of the real existence of repulsive forces exerted by the sun with great energy under certain conditions and upon certain forms of matter. A source of perplexity exists, however, in the relative narrowness of these beams, whose apparent cross-section, as delineated by most observers, is far less than the apparent diameter of the sun. One would thus be led to infer that the real seat of these repulsive energies lies far beneath the solar photosphere. It is worthy of notice, too, that the beams usually appear to extend from the zone of spots; and one might almost infer that the repulsive action is exerted with peculiar energy in lines extending from the sun's centre towards the so-called spot-zone.

It is with reference to such questions as these that the observation of the present and future solar eclipses is so full of interest. There are problems presented by the corona which are as yet not only unsolved, but apparently very far from solution. All the energies of our observers need to be directed towards the mastery of these difficulties; and therefore it is that, as I think, I have been right in urging as earnestly as possible that the records of past eclipses should be made to bear fruit in the interpretation of all problems which can be interpreted by means of them, while the opportunities afforded by future eclipses, and the skill of those who observe them, should be wholly devoted to those more perplexing problems which still await even the means of solution.

The news has just arrived that the Sicilian party will be dis

tributed among four stations-one party will be at Syracuse, another at Augusta, a third (the head-quarters) at Catania, and a fourth, a strong party headed by Professor Roscoe, at the summit of Etna. Although this arrangement is associated in the telegram with the accident which happened to the Psyche (the news of which sent a thrill of alarm and anxiety through the hearts of all who take interest in the cause of science), I am disposed to hope that some parts of the arrangement may be referred to other considerations. The fact that a portion of the expedition is able to travel so far south as Syracuse, actually crossing the line of central eclipse, seems to imply that the expedition has not been seriously hampered by the accident. hope much from the party at Etna. I had dwelt earnestly on the advisability of sending a party there (see the December number of "Fraser's Magazine"), and I think it cannot be doubted that, though the totality will last there but a short time, more instructive observations of the corona will be possible at so considerable an elevation than any which have yet been made.