KEVELATIONS OF SPECTRUM-ANALYSIS. 283 



round the still molten surface of the Sun, there probably 

 exists a stratum of dense aeriform matter, made up of sub 

 limed metals and metallic compounds, and above this a 

 stratum of comparatively 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 mat 

 ters 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 vapour, but must con 

 dense and precipitate. Meanwhile the upper stratum, ha 

 bitually 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. 



Since the foregoing paragraph was originally published, 

 in 1858, the proposition it enunciates as a corollary from 

 the Nebular Hypothesis, has been in great part verified. 

 The marvellous disclosures made by spectrum-analysis, 

 have proved beyond the possibility of doubt, that the solar 

 atmosphere contains, in a gaseous state, the metals, iron, 

 calcium, magnesium, sodium, chromium, and nickel, along 

 with small quantities of barium, copper, and zinc. That 

 there exist in the solar atmosphere other metals like those 

 which we have on the Earth, is probable ; and that it con 

 tains elements which are unknown to us, is very possible. 



Be this as it may, however, the proposition that the 

 Sun s atmosphere consists largely of metallic vapours, must 

 take rank as an established truth ; and that the incandes- 

 eent body of the Sun consists of molten metals, follows al 



