rendered visible by its superior blackness; a circumstance which proves that the light of the corona must be considerably stronger than the illuminated atmosphere near the Moon's place, even when a portion of the Sun's direct light is falling upon the air there.

The total eclipse of August 1867 attracted very much less attention than those which occurred during the same month of the two following years. Yet the observations made by Herr Grosch, of the Santiago observatory, Chili, in conjunction with Vice-Director Vergaza and Lieut. Vidal, are full of significance in connection with the main object of this chapter, which is the determination of the true theory of the corona. At the moment when totality began, there appeared,' says Herr Grosch,† 'around the Moon a reddish glimmering light, similar to that of the aurora, and almost simultaneously with this (I mean very shortly after it) the corona. This reddish glimmer,

which surrounded the Moon with a border of the breadth of at most five minutes, was not sharply bounded in any part, but was extremely diffused, and less distinct in the neighbourhood of the poles. I can decidedly confirm this at least as regards the Sun's north point, but not so much so of the south point, as that part was less observed by me, but was more particularly attended to by Lieutenant Vidal,

* By the atmosphere near the Moon's place, I mean that part of the atmosphere which lies nearly in the same direction as the Moon. Of course it is, in reality, very far removed from the Moon's true place.

+ I quote (from the Student for March 1869) Mr. Lynn's translation of Herr Grosch's narrative.

who could not afterwards give any more positive information concerning this phenomenon. . . . To speak now of the corona:-its extent was considerably longer in the direction of the Sun's equator; and in considering its nature, we must, I believe, look upon it as decidedly unconnected with him.* Whereas, in the direction of its poles, its apparent height exceeded that of the Moon by only a third of her diameter; in the direction at right angles to this, its extent amounted to four-fifths of that diameter. Its light was white, brighter on the Moon's limb, and becoming gradually fainter on the other side. This white light was not in the least radiated itself, but it had the appearance of rays penetrating through it; or rather as if rays ran over it, especially in the direction of east and west, forming symmetrical pencils diverging outwards and passing far beyond the boundary of the white light. These rays had a more bluish appearance, and might best be compared to those produced by a great electro-magnetic light. Their similarity to these indeed was so striking that under other circumstances I should have taken them for such, shining at a great distance. The view of the corona here described is that seen with the naked eye. I employed but a very short time upon it, only as much, in fact, as was necessary to obtain a mere momentary view of the general appearance of the totality. And now, in

* Herr Grosch obviously does not mean that the corona is not, in his opinion, a solar appendage, but that there is no continuous connection between the Sun and the corona; that it is not, in fact, of the nature of a solar atmosphere.

conclusion, I would just mention another phenomenon, which seemed to me too important to pass unnoticed. It showed itself exactly at the north point of the Sun. In the white light of the corona, close upon the Moon's limb, there appeared several dark curves. They were symmetrically arched towards the east and west, sharply drawn, and resembling in tint lines drawn with a lead pencil upon white paper. They gave the impression as if they proceeded from one point, which point was on the other side of the Moon; not, however, on the limb, but somewhat nearer the centre of the Sun. Beginning at the distance of one minute, they could be traced up to about nine minutes from the Moon's limb. Throughout the duration of the eclipse they underwent no alteration whatever, remaining constant both in form and colour until the disappearance of the corona. Lieutenant Vidal (agreeing with Signor Vergaza) speaks of a similar appearance, exactly at the south point, in the form of a fan or sheafformed tuft of light; but he says nothing of characteristic dark curves, such as I saw at the north point. There is, however, no cause to doubt the accuracy of the observed facts. These dark curves indicate a strong magnetic polar force of the Sun, so that an appearance of the kind in question might be seen at the south as well as at the north point; but perhaps being less developed at the former than at the latter, it was less perceptible.'

It is impossible to read this account without feeling how much might be learned from a systematic survey

of the corona during any considerable total eclipse. Here were three observers only, who each gave to the

corona but a fugitive attention, and yet their accounts agree in pointing to the existence of appearances which merited a thorough study during the whole continuance of totality, and that not by two or three observers only, but by ten or twelve at least, each appointed to the investigation of some special feature.

The study of the corona was one of the subjects to which the attention of the observers sent out to view the great eclipse of August 1868 was specially directed. More seems to have been hoped from the application of spectroscopic and polariscopic analysis than from direct observation; and, accordingly, the best accounts we have of the general aspect of the corona are those derived from observers not belonging to the expeditionary parties. We owe to the professors of the college of Manilla, who observed the eclipse at Mantawalok, the accompanying very remarkable drawing of the corona. It is important to notice that, unlike most pictures of the corona, this one can be trusted. Owing to the want of success which had attended all attempts to photograph the corona, the professors were led to think of an ingenious plan for obtaining exact drawings. They prepared beforehand several sheets of paper, which were introduced one after another into a dark chamber, so that the image of the eclipsed Sun fell upon them, and the features of the corona were rapidly sketched out on each. The corona is described as of a somewhat triangular aspect; yet it is to be noticed that there are four rays of the longer sort, so that the corona in this case, as in so