< Page:Popular Science Monthly Volume 1.djvu
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THE SPOTS ON THE SUN.

separates the intense heat of the interior portions of the sun from the cold surrounding space. He holds to powerful ascending and descending currents, which result here and there in breaks and dispersions by which openings are made to the gaseous interior, giving the appearance of spots; to which Kirchhoff replies that an incandescent interior, at so high a temperature, would certainly be luminous.

In 1858, before the views of either Kirchhoff or Faye were announced, or spectrum analysis had been applied to the subject, Mr. Herbert Spencer published an article on "Recent Astronomy and the Nebular Hypothesis," in which he anticipated some of the most important results that have been arrived at since by others. He took the ground that the sun is still passing through that incandescent stage which all the planets have long ago passed through, the lateness of his cooling being due to the immensely greater ratio of his mass to his surface. He supposes the sun to have now reached the state of a molten shell with a gaseous nucleus; and that this shell is ever radiating its heat, but is sustained at its high temperature by the progressive condensation of the sun's total mass.

As respects the solar atmosphere, Mr. Spencer said in 1858:

"If we consider what must have been the state of things here when the surface of the earth was molten, we shall see that, round the still molten surface of the sun, there probably exists a stratum of dense aëriform matter, made up of sublimed metals and metallic compounds, and above this a stratum of comparative rare medium analogous to air. What now will happen with these two strata? Did they both consist of permanent gases, they could not remain separate: according to a well-known law, they would eventually form a homogeneous mixture. But this will by no means happen when the lower stratum consists of matters that are gaseous only at excessively high temperatures. Given off from a molten surface, ascending, expanding, and cooling, these will presently reach a limit of elevation above which they cannot exist as vapor, but must condense and precipitate. Meanwhile, the upper stratum, habitually charged with its quantum of these denser matters, as our air with its quantum of water, and ready to deposit them on any depression of temperature, must be habitually unable to take up any more of the lower stratum; and therefore this lower stratum will remain quite distinct from it. We conclude, then, that there will be two concentric atmospheres, having a definite limit or separation."

This view was sustained in the most remarkable manner, by the subsequent discoveries, through spectrum analysis, of the metals iron, calcium, magnesium, sodium, chromium, and nickel, in a gaseous state in the atmosphere of the sun.

As respects the solar spots, in the article above quoted, Mr. Spencer suggested that they were due to cyclonic action. He has subsequently developed this view, which is now regarded as the most rational explanation we have of the cause of solar spots. In the latest edition of "The Heavens," by Guillemin, published last year, translated by Lockyer, and edited by Proctor, after a review of the subject, and an examination of all the theories that have been pro-

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