58 THE POPULAR SCIENCE MONTHLY. 



duced from terrestrial experiments, to determine solar temperatures : 

 such a proceeding is an unsound and unwarrantable extrapolation, 

 likely to lead to widely erroneous conclusions. 



For my own part, I feel satisfied as to the substantial correctness 

 of the generally received theory of the sun's constitution, which re- 

 gards this body as a great ball of intensely heated vapors and gases, 

 clothed outwardly with a coat of dazzling clouds formed by the con- 

 densation of the less volatile substances into drops and crystals like 

 rain and snow. Yet it must be acknowledged that this hypothesis is 

 called in question by high authorities, who maintain, with Kirchhoff 

 and Zollner, that the visible photosphere is no mere layer of clouds, 

 but either a solid crust, or a liquid ocean of molten metals ; and there 

 may be some who continue to hold the view of the elder Herschel 

 (still quoted as authoritative in numerous school-books), that the cen- 

 tral core of the sun is a solid and even habitable globe, having the 

 outer surface of its atmosphere covered with a sheet of flame main- 

 tained by some action of the matter diffused in the sj)ace through 

 which the system is rushing, "We must admit that the question of the 

 sun's constitution is not yet beyond debate. And not only the consti- 

 tution of the sun itself, but the nature and condition of the matter 

 composing it, is open to question. Have we to do with iron and 

 sodium and hydrogen as we know them on the earth, or ^re the solar 

 substances in some different and more elemental state ? 



However confident many of us may be as to the general theory of 

 the constitution of the sun, very few, I imagine, would maintain that 

 the full explanation of sun-spots and their behavior has yet been 

 reached. "We meet continually with phenomena which, if not really 

 contradictory to prevalent ideas, at least do not find in them an easy 

 explanation. So far as mere visual aj^pearances are concerned, I think 

 it must be conceded that the most natural conception is that of a dark 

 chip or scale thrown up from beneath, like scum in a caldron, and float- 

 ing, partly submerged, in the blazing flames of the photosphere which 

 overhang its edges, and bridge across it, and cover it with filmy veils, 

 until at last it settles down again and disappears. It hardly looks like 

 a mere hollow filled with cooler vapor, nor is its appearance that of a 

 cyclone seen from above. But then, on the other hand, its spectrum 

 under high dispersion is very peculiar ; not at all that of a solid, heated 

 slag, but it is made up of countless fine dark lines, packed almost in 

 contact, showing, however, here and there, a bright line, or at least an 

 interspace where the rank is broken by an interval wider than that 

 which elsewhere separates the elementary lines — a spectrum which, so 

 far as I know, has not yet found an analogue in any laboratory experi- 

 ment. It seems, however, to belong to the type of absorption spectra, 

 and to indicate, as the accepted theory requires, that the spot is dark 

 in consequence of loss of light, and not from any original defect of 

 luminosity. Here, certainly, are problems that require solution. 



