CELESTIAL CHEMISTRY. 373 



I do not want to take up more time in considering the central 

 luminary of our solar system, or I would take you back from 

 the outer corona to that part of the sun which to the common- 

 place man is apparently of more practical importance, namely, 

 the photosphere, that inner globe, or shell, which is the source 

 and bearer of the light and heat that we derive from the sun. 

 I would show you how, deducing our results from observations 

 made by the spectroscope, we at length come to the only 

 possible conclusion that the photosphere consists of clouds — 

 mist or fog, if you will — and perhaps rain, of white hot particles 

 of carbon. These are constantly being volatilised at the 

 enormous temperature of the sun's surface, exactly as water 

 evaporates from our own lakes and oceans ; they accumulate as 

 dense incandescent clouds in the sun's atmosphere, and rain 

 down again from the latter in showers of liquid fire. The solar 

 storms and gales are, on a gigantic scale, very much like those 

 of earth, except that the rain and fog which they bring consist 

 not of cool water, but of fiery carbon. 



To summarise what the spectroscope has taught us regarding 

 the "chemistry of the sun — the sun's disc, as we see it, ordinarily 

 represents what is called the photosphere. It is a shell, we may 

 say. of incandescent clouds of carbon. Of the core of this shell 

 we know nothing except by mere inference. The carbon clouds 

 of the photosphere are so dense that we cannot see what 

 ■exists beneath them. Outside the photosphere are the 

 successive layers of the sun's atmosphere : first of all comes 

 what we have called the reversing layer ; it is that which 

 introduces into the solar spectrum the dark lines, due to the 

 vapours of iron, lead, and many other metals with which this 

 reversing layer is very heavily laden. If this layer were not 

 there, the photosphere beneath would give an absoluteh 

 continuous spectrum. Enveloping the reversing layer is the 

 chromosphere, consisting of incandescent hydrogen, and of 

 glowing magnesium and calcium vapour. Outside of that 

 again, and stretching to as much as three times the sun's 

 diameter on either side, extends the corona, in which the gas 

 lielium, comparatively recently discovered on earth, is present, 

 as well as the yet undiscovered gas coronium. 



The moon and planets, which shine by the sun's light 

 reflected from their own surfaces, naturally show\ for that 

 reason, the same spectrum as the sun. and, as may therefore 

 be expected, their spectra are crossed by the same dark lines. 



More than forty years have elapsed since Sir William Huggins 

 first turned his enquiring spectroscope from the brilliant blaze 

 of the sun to the lesser lights of the planets and fixed stars. 

 The difficulties of such an investigation, in view of the tiny 

 specks of light presented by these other heavenly bodies, can 

 well be understood, but a wonderful amount of success has all 

 along attended these investigations, and Dr. Huggins, as he 

 then was, arrived at the conclusion that the planets Mars, 

 Jupiter, and Saturn all possessed atmospheres of their own 

 because their spectra showed dark lines which were not to be 

 found in the solar spectrum. Even that aggregation of fine 

 particles that constitutes the well-known triple ring system of 



