not unduly shortened the exposure for each. Again there were obvious signs in the best of the photographs that at Lord Lindsay's station a haze or some other atmospheric cause had tended to mar the distinctness of the corona; for the disc of the moon, especially on the side where the corona was brightest, was illuminated with a light far too strong to be otherwise explained (assuming always that all the photographic operations had been satisfactorily performed).

But after this meeting attention was directed to a photograph taken by the American observers at a station close by. In this photograph only a portion of the corona 2 was shown; but the extension of the corona was considerably greater than in any photographs which had hitherto been taken; and there, in the south-eastern quadrant, was that very V-shaped gap of which the observers had spoken, and which Lieut. Brown and others had depicted. It was not a mere faintly-seen or perhaps half-suspected feature, but the most striking feature in the photograph.

One thing only was required to remove all shadow of doubt. News had reached England that Mr. Brothers had been most successful in photographing the corona at his station near Syracuse. In the fifth

I wrote this under correction; the complete series of photographs not being available for examination at the time. Certainly, though complete success may not have rewarded Lord Lindsay's exertions, there can be no question of the degree of credit due to him. At one time it seemed probable that his expedition, set forth at his own charge, would be the only one to uphold the scientific credit of our country.

? I do not mean that the outer part had failed to appear on the glass, but that the glass only included the inner half.

plate of six he had taken, the corona is shown,' said the account, as it was never seen on glass before.'

Here a crucial test seemed available. If the great gap opposite the south-eastern quadrant was not seen in this photograph, negative evidence, about as strong as negative evidence could be in this case, would be supplied against the theory that the radiations are true solar appendages. On the other hand, if the great gap appeared in the photograph, then positive evidence of the most convincing kind would be afforded on this interesting question.

I was so fortunate as to be the first to receive intelligence on this point. Mr. Brothers forwarded, through me, to Dr. Huggins, a rough drawing of his best photograph, and in that picture the V-shaped gap appears as the most striking feature of the corona. It is more plainly shown than in the American photograph, and its borders can be traced very much farther from the sun. The photograph, indeed, fairly bears out the statement that the corona is shown as it was never seen on glass before; it is facile princeps among photographs of the corona; but, except in this greater clearness and extension, the figure of the great gap and of the bounding radiations agrees perfectly with the American photograph.

At length, then, we have evidence which cannot be questioned on this long-mooted point. The corona itself has left us an unmistakable record, has written down in the plainest possible characters a statement of its true nature. By a piece of good fortune such as

few were so sanguine as to anticipate, a feature strongly marked enough to be recognisable beyond the possibility of question has been depicted in two exceptionally successful photographs, taken at widely separated stations. This one feature proves all that we require. Granted that two radiations (for the gap implies necessarily the existence of two bounding rays) exist in some real solar appendage, it will no longer be doubted that radiations of the same nature exist all round the sun. Nor will it now be questioned that the faint prolongations of such radial beams, seen when eclipses are viewed under very favourable circumstances, belong also to this solar appendage. Those expansions of the four-cornered corona in 1869, which General Myer, stationed 5,000 feet above the sea-level, was able to trace to a distance of two or three diameters of the moon's disc,' must now be regarded as indubitably appertaining to some solar appendage. For the faint shadow of doubt which hung over the concurrent accounts of the figure of the corona during the American eclipse has been fairly dissipated by the testimony now obtained; and once admitting the coronal projections seen at lower stations as belonging to a solar appendage, the extensions of those projections seen by observers above the denser atmospheric strata must of course equally be associated with that appendage. The fixity of those four far-reaching extensions during the four minutes of totality, as also the fixity of the far-reaching extensions seen during the Swedish eclipse of 1736, not only during totality,

but for several seconds afterwards, can now be understood. Astronomers have not had to deal, in these and other instances, with beams shining through our own atmosphere, but with illuminated regions of space exceeding the sun's own orb many times in volume.

As to the physical meaning of the coronal phenomena, I refrain at present from speaking. The subject is one of wide extent, and could not fitly be treated at the close of such a paper as the present. The interpretation of the coronal radiations is connected, I believe, with the subject of meteoric astronomy already dealt with in these pages, with the phenomena of our own auroras, with the zodiacal light, with cometary systems, and finally with those strange laws according to which magnetic and auroral phenomena are associated with the disturbance of the solar photosphere. The task of duly presenting these interwoven relations must be left to another occasion.

Fraser's Magazine, March 1871

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WHAT, THEN, IS THE CORONA?

It is not easy for a thoughtful mind to study the evidence bearing on any scientific subject without being led to theorise. Even though the evidence be imperfect, even though-however carefully sifted and analysed-it still leave the problem indeterminate, the mind will yet weigh fact against fact, and probability against probability, adopting then, though but provisionally, the theory which seems best to accord with such facts as have been revealed. As fresh facts are ascertained, the theory may have to be modified or even abandoned; and often one theory after another may thus be adopted for a while and presently rejected; yet it is only by thus theorising-boldly, but with due deference to facts-that the truth can finally be established. There is no recorded instance so far as I know of any difficult problem in science which has been mastered otherwise than by resolute and industrious theorising based on the careful study of all the observed facts bearing upon the subject matter. So Copernicus was enabled to place the sun at the centre of the planetary scheme; so Kepler assigned to the planets the laws according to which they move; so Newton was able to discover the mainspring of the universe. No otherwise, again, did Römer learn how to measure the velocity of light, or Bradley find a