42 C. S. Hastings— Constitution of the Sun. 
that the substance in question, so far as we know it, has prop- 
erties similar to those of the carbon group. 
1ave given plausible explanations of all the phenomena in- 
cluded specially in my own observations. It remains to dis- 
cuss the others, briefly mentioned above. 
e substance precipitated cools very rapidly, as it is an 
excellent radiator, separated from space only by extremely dia- 
thermous media. It forms then a smoke-like envelop, which 
ought to exert just such a general absorption as that observed 
at the limb of the sun. Itis thin because of the relatively 
great density of the substance in the liquid or solid state; thus 
the apparent brilliancy of the facule is readily understood. 
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 
this point, there exercising a marked general absorption which 
would betray itself as a spot. At this place the suspended par- 
ticles would sink to lower levels with constantly increasing 
temperature, until finally, heated to intense incandescence, they 
would revolatilize. Thus the floor or substratum of every spot 
must be a portion, depressed it is true, of the photosphere. All 
the spectroscopic phenomena of spots, which have proved so 
perplexing, are thus naturally and easily explained. . 
In the immediate neighborhood of a spot, the centripetal 
currents bend down the ordinary convection or granule-produc- 
ing currents, so that they are approximately level. Before, the 
latter cooled suddenly by rarefaction in their upward course, 
now they cool mainly by the much slower process of radiation ; 
thus, while before the locus of precipitation was restricted, It 
is now greatly extended. This is the cause of the great elon- 
gation of the granules in the penumbra, a real elongation, I 
imagine, and not merely an apparent one. 
inally, concerning the close duplicity of certain lines, we 
may reason thus:—If we could surround the sun by a stratum 
of gas hotter’ than the photosphere and much rarer than that 
producing the corresponding Fraunhofer lines, we should, as 18 
shown by a course of reasoning which I have given in another 
place,* see each dark line divided by a sharp bright line in Its 
center, that is, doubled. But as a consequence of the theory, 
this supposed condition must be practically met in the case 
certain vapors in the sun. The gases just over the granules, 
in the vertical currents, are at a very high temperature, essed" 
tially that of the condensing material itself, consequently much 
hotter and rarer than the relatively low-lying vapors which, a 
we have seen, produce the Fraunhofer lines 
* On Lockyer’s Hypothesis, Am. Jour. Chem., vol. i, p. 15. 
