What astonishes one most about the solar radiation, is the immense amount of it that is apparently wasted into space in comparison with what falls directly upon the bodies of the solar system. Only about the one-hundred-millionth is caught by all the planets together. What becomes of the rest we cannot tell. That brilliant white body of the sun, which we see, is enveloped by several layers of gases and vaporous matter, in the same manner as our globe is enveloped by its atmosphere (see Fig. 10, p. 131). These are transparent, just as our atmosphere is transparent; and so we see the white bright body of the sun right through them. This white bright portion is called the _Photosphere_. From it comes most of that light and heat which we see and feel. We do not know what lies under the photosphere, but, no doubt, the more solid portions of the sun are there situated. Just above the photosphere, and lying close upon it, is a veil of smoke-like haze. Next upon this is what is known as the _Reversing Layer_, which is between 500 and 1000 miles in thickness. It is cooler than the underlying photosphere, and is composed of glowing gases. Many of the elements which go to make up our earth are present in the reversing layer in the form of vapour. The _Chromosphere_, of which especial mention has already been made in dealing with eclipses of the sun, is another layer lying immediately upon the last one. It is between 5000 and 10,000 miles in thickness. Like the reversing layer, it is composed of glowing gases, chief among which is the vapour of hydrogen. The colour of the chromosphere is, in reality, a brilliant scarlet; but, as we have already said, the intensely white light of the photosphere shines through it from behind, and entirely overpowers its redness. The upper portion of the chromosphere is in violent agitation, like the waves of a stormy sea, and from it rise those red prominences which, it will be recollected, are such a notable feature in total solar eclipses. [Illustration: FIG. 10.--A section through the Sun, showing how the prominences rise from the chromosphere.] The _Corona_ lies next in order outside the chromosphere, and is, so far as we know, the outermost of the accompaniments of the sun. This halo of pearly-white light is irregular in outline, and fades away into the surrounding sky. It extends outwards from the sun to several millions of miles. As has been stated, we can never see the corona unless, when during a total solar eclipse, the moon has, for the time being, hidden the brilliant photosphere completely from our view. The solar spectrum is really composed of three separate spectra commingled, _i.e._ those of the photosphere, of the reversing layer, and of the chromosphere respectively.