It is noteworthy that several careful observers of the corona in 1842 believed that they could recognise motion in the coronal rays. Francis Baily compared the appearance of the corona to the flickering light of a gas illumination. O. Struve also was much struck by the appearance of violent agitation in the light of the ring. It seems probable that the appearance was due to movements in that part of our atmosphere through which the corona was observed. The extent of the corona was variously estimated by different observers. Petit, at Montpelier, assigned to it a breadth corresponding to a height of about 200,000 miles; Baily a height of about 500,000 miles; and O. Struve a height of more than 800,000 miles. The last-named observer also recognised luminous expansions extending fully four degrees (corresponding to nearly seven million miles) from the sun. Picozzi, at Milan, noticed two jets of light, which were seen also by observers in France. Rays also were seen by Mauvais at Perpignan, and by Baily at Paria. But Airy, observing the corona from the Superga, could see no radiation; he says '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.' These varieties in the aspect of the corona were doubtless due to varieties in the condition of the atmosphere through which the corona was seen. Now it cannot be questioned that, so far as extension is concerned, the corona seen in 1842 was one which, if the theory we are considering were sound, we should expect to see near the time of maximum rather than of minimum solar disturbance. On the other hand, in brightness the corona of 1842 resembled, if it did not surpass, that of July 1878.
'I had imagined,' says Baily, 'that the corona, as to its brilliant or luminous appearance, would not be greater than that faint crepuscular light which sometimes takes place (sic) 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.'
The light of the corona was so bright, O. Struve states, 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.' Thus while as to extent the corona in 1842 presented the appearance to be expected at the time of maximum solar disturbance, if our theory is sound, its brightness was that corresponding to a time of minimum disturbance. Its structure corresponded with the former condition. The light of the corona was not uniform, nor merely marked by radiations, but in several places interlacing lines of light could be seen. Arago, at Perpignan, observed with the unaided eye a region of the corona where the structure was as of intertwined jets giving an appearance resembling a hank of thread in disorder.
Certainly, for an eclipse occurring two years from the time of minimum, and five years from the time of maximum disturbance, that of July, 1842,[1] has not supplied evidence favouring the theory with which we started. Whether any other theory of association between the corona and the sun-spots will better accord with the evidence hitherto collected remains to be seen.
Turn we now to the eclipse of 1851, occurring nearly midway between the epochs of maximum solar disturbance (1848) and minimum solar disturbance (1856). I take the account given by Airy, our Government astronomer, as he was one of the observers of the eclipse of 1842.
'The corona was far broader,' he says, '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 indefinitely—in 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.'
The corona thus described belongs to that which our theory associates with the period of maximum rather than of minimum solar disturbance. Definite peculiarities of structure seem to have been more numerous and better marked than in 1842. It accords with our theory that 1851 was a year of greater solar disturbance than was observed in 1842, as the following numbers show:—
| Days of observation | Days without spots | New groups observed | |
| 1842 | 307 | 64 | 68 |
| 1851 | 308 | 0 | 141 |
| 1860 | 332 | 0 | 211 |
I have included the year 1860, as we now proceed to consider the corona then seen by Airy. The year 1860 did not differ very markedly, it will be observed, from 1851, as regards the number of new groups of spots observed by Schwabe, especially when account is taken of the number of days in which the sun was observed in these two years. But 1860 was a year of maximum solar disturbance, whereas 1851 was not.[2]
Airy remarks of the corona in 1860:—'It gave a considerable body, but I did not remark either by eye-view or by telescope-view anything annular in its structure; it appeared to me to resemble, with some irregularities (as I stated in 1851), the ornament round a compass-card.'