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Let us now recapitulate what makes up the sun as we see and know it.

We have first the vast interior of the globe which, of course, we can never see.

What we see when we look at the sun is the shining surface of this globe, the photosphere. It is not a real surface, but more likely a gaseous layer several hundred miles deep which we cannot distinguish from a surface. This layer is variegated by spots, and in or over it rise the faculæ.

On the top of the photosphere rests the layer of gases called the chromosphere, which can be observed at any time with a powerful spectroscope, but can be seen by direct vision only during total eclipses.

Through or from the red chromosphere are thrown up the equally red flames called the prominences.

Surrounding the whole is the corona.

Such is the sun as we see it. What can we say about what it really is? First, is it solid, liquid, or gaseous?

That it is not solid we have already shown by the law of rotation. It cannot be a liquid like molten metal, because it sends off from its surface such a flood of heat as would cool off and solidify molten metal in a very short time. For more than thirty years it has been understood that the interior of the sun must be a mass of gas, compressed to the density of a liquid by the enormous pressure of its superincumbent portions. But it was still supposed that the photosphere might be in the nature of a