THE SPOTS ON THE SUN. 153 



separates the intense heat of the interior portions of the sun from the 

 cold surrounding space. He holds to powerful ascending and descend- 

 ing currents, which result here and there in breaks and dispersions by 

 which openings are made to the gaseous interior, giving the appear- 

 ance 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 an- 

 nounced, 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 impor- 

 tant 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 mol- 

 ten 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 sur- 

 face of the sun, there probably exists a stratum of dense aeriform 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 homo- 

 geneous 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. Spen- 

 cer suggested that they were due to cyclonic action. He has subse- 

 quently 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, trans- 

 lated by Lockyer, and edited by Proctor, after a review of the sub- 

 ject, and an examination of all the theories that have been pro- 



