hydrogen cloud by the sun's edge (fig. 1). This cloud was about 100,000 miles long; and its upper surface was some 50,000 miles, the lower surface about 15,000 miles, above the sun's surface. The whole had the appearance of being supported on pillars of fire;

these seeming pillars being in reality hydrogen jets, brighter and more active than the substance of the cloud. At half-past twelve, when Professor Young chanced to be called away from his observatory, there were no indications of any approaching change, except

that one of the connecting stems of the southern extremity of the cloud had grown considerably brighter, and was curiously bent to one side; and near the base of another, at the northern end, a little brilliant lump had developed itself, shaped much like a summer thunderhead.'

6

But when Professor Young returned, about half an hour later, he found that a very remarkable change had taken place, and that a very remarkable process was actually in progress. The whole thing had been literally blown to shreds,' he says, 'by some inconceivable uprush from beneath (fig. 2). In place of the quiet cloud I had left, the air-if I may use the expression-was filled with flying débris, a mass of detached vertical fusiform fragments, each from ten to thirty seconds (i.. from 4,500 to 13,500 miles) long by two or three seconds (900 or 1,350 miles) wide, brighter and closer together, where the pillars had formerly stood, and rapidly ascending. When I looked some of them had already reached a height of nearly four minutes (100,000 miles); and while I watched them, they rose with a motion almost perceptible to the eye, until in ten minutes the uppermost were more than 200,000 miles above the solar surface. This was ascertained by careful measurements, the mean of three closely accordant determinations giving 210,000 miles as the extreme altitude attained. I am particular in the statement, because, so far as I know, chromatospheric matter (red hydrogen in this case) has never before been observed at an altitude exceeding five minutes, or

135,000 miles.

The velocity of ascent also-167

miles per second--is considerably greater than anything hitherto recorded. As the filaments rose, they

gradually faded away like a dissolving cloud, and at a quarter past one, only a few filmy wisps, with some brighter streamers low down, near the chromatosphere, remained to mark the place. But in the meanwhile the little "thunderhead " before alluded to had grown

and developed wonderfully into a mass of rolling and ever-changing flame, to speak according to appearances. First it was crowded down, as it were, along the solar surface; later (fig. 3) it rose almost pyramidally fifty thousand miles in height; then its summit was drawn down into long filaments and threads (fig. 4), which were most curiously rolled backwards and forwards like the volutes of an Ionic capital; and finally it faded away, and by half-past two had vanished like the other. The whole phenomenon,' adds Professor Young, 'sug

This, however, is a mistake, since Respighi had already seen prominences reaching to a height of 160,000 miles.

gested most forcibly the idea of an explosion under the great prominence, acting mainly upwards, but also in all directions outwards, and then, after an interval, followed by a corresponding inrush; and it seems far from impossible that the mysterious coronal streamers, if they turn out to be truly solar, as now seems likely, may find their origin and explanation in such events.'

Here the complete narrative of this stupendous solar outburst has been given because the event requires to be thoroughly understood in its general relations, in order that inferences from details may have their full weight. But the point which mainly concerns us in the above account is the actual observed velocity with which the hydrogen wisps travelled upwards. This velocity is estimated by Professor Young at 167 miles per second; but his estimate relates only to the average velocity with which a certain range was traversed, not to the maximum velocity within that

range, and still less to the initial velocity of ejection, which (even according to the ordinary law of projected bodies) must have beer considerably greater. It will be remembered that such a velocity as 300 miles per second would be required for the ejection of matter to distances corresponding to the observed extension of the corona. It can now be shown that matter must have moved with such a velocity-nay, with a much greater velocity-during the eruption witnessed by Professor Young.

I may premise that it is by no means to be regarded as certain perhaps it is scarcely probable-that the hydrogen seen travelling upwards was itself erupted. matter. It may have been merely following the track of the matter actually erupted, being carried along that track by the currents generated during the inconceivably rapid outrush of the erupted matter. In this case we can safely infer an even greater velocity of outrush than would be deduced if we regarded the hydrogen as itself erupted.

Again, it is not certain that the eruption, whatever may have been its nature, took place actually at the edge or very close to the edge of the sun's visible hemisphere. If the scene of the eruption were at any considerable distance from the edge, the motion of the hydrogen wisps must have been, to some extent, foreshortened. In this case a greater range was in reality traversed, and the average velocity, as well as the inferred initial velocity, would be so much the greater.

Yet, again, Professor Young saw hydrogen wisps