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forms are remarkably like those which iron filings assume when scattered on paper above a magnet. It is therefore a question whether there is not here something in the nature of a magnetic force. But in the region called the sun's equator this analogy ceases to hold. In describing the sun we mentioned the much greater activity in the regions of greater spottedness than elsewhere. It now seems as if the forces which throw out the corona are also greatest where the sun's activity is greatest.

The probability now seems to be that the corona is composed of matter thrown up from the sun, and kept from falling back again by the repulsion of the solar rays, and that it bears a certain resemblance to the tail of a comet.

A very important question is whether the corona shines mostly by reflected light, or by its own light, due to the high temperature which it must have so near the sun. No doubt its light arises from both sources, but it is not yet known in what proportion. The fact is that its spectrum shows some bright lines. These can be due only to the light of the matter itself. Some observers have supposed that they also saw dark lines in the spectrum. This, however, has not been proved. On the whole the probability seems to be that the corona shines mostly by its own light.