100 Mr. C. S. Hastings's Theory of 



coming from the sun is radiated by solid or liquid particles of 

 carbon just at the point of vaporization, let us see if the facts 

 of observation fulfil the implied conditions. 



As a first consequence, we see that the temperature and 

 light of the photosphere are defined as those of solid carbon 

 at the point of volatilization. In the electric arc there is a 

 very small area of the positive carbon-pole at this high tem- 

 perature. Though this area is in a very disadvantageous 

 position for observation, and can consequently have but a dis- 

 proportionally small share in producing the total effect, the 

 splendour of the electric light might almost tempt us to believe 

 the guess a valid one. Another consequence implied, how- 

 ever (namely, that the spectral lines proper to simple carbon 

 are absent in the solar spectrum), is doubtless better adapted as 

 a crucial test of the hypothesis than a study of the electric 

 light. There has been evidence recently offered that carbon- 

 lines are present in the solar spectrum. Granting this, we 

 perceive that the photosphere contains solid or liquid particles 

 hotter than carbon vapour, and consequently not carbon. 



I am then inclined to suspect that the photospheric material 

 may be silicon, which, though denser in the gaseous state than 

 carbon, is not improbably more abundant. There is also good 

 reason to suppose that carbon is precipitated at a higher level; 

 and the analogous, but less common, element boron may add a 

 minor effect. 



In the explanations which I shall give of the remaining 

 phenomena, it may serve to fix the ideas to think of the gra- 

 nules which characterize the sun's photosphere as clouds of a 

 substance like precipitated silicon. At any rate we are sure 

 that the substance in question, so far as we know it, has pro- 

 perties similar to those of the carbon group. 



I have given plausible explanations of all the phenomena 

 included specially in my own observations. It remains to dis- 

 cuss the others, briefly mentioned above. 



The substance precipitated cools very rapidly, as it is an 

 excellent radiator, separated from space only by extremely 

 diathermanous media. It forms, then, a smoke-like envelope 

 which ought to exert just such a general absorption as that 

 observed at the limb of the sun. It is thin, because of the 

 relatively great density of the substance in the liquid or solid 

 state ; thus the apparent brilliancy of the faculse is readily 

 understood. 



If there is any disturbing cause which would tend to direct 

 currents of gas, over a considerable area of the solar surface, 

 toward a point, this smoke, instead of quietly settling down 

 to lower levels between the granules, would concentrate about 



