246 THE CHEMISTRY OF THE SUN. [CHAIV 



That was one point. 



Here is the next point which made an appeal to the stars so 

 necessary. 



"We are justified in supposing that our terrestrial calcium once 

 formed is a distinct entity, whether it be an element or not, and, 

 therefore, by working at terrestrial calcium alone we shall never 

 know, even if its dissociation be granted, whether the temperature 

 produces a simpler form, a more atomic condition, of the same thing, 

 or whether we are able to break it up into x + y, because in our 

 terrestrial calcium, assuming all calcium to be alike, neither x nor y 

 will ever vary ; but if calcium be a product of a condition of rela- 

 tively lower temperature, then in the stars hot enough to enable its 

 constituents to exist uncompounded, we may expect these constitu- 

 ents to vary in quantity ; there may be more of x in one star and 

 more of y in another ; and if this be so, then the H and K lines will 

 vary in thickness, and the extremest limit of variation will be that 

 we shall only have H, representing, say, x in one star, and only have 

 K, representing, say, y in another. Intermediately between these 

 extreme conditions we may have cases in which, though both H 

 and K are visible, H is thicker in some and K is thicker in others." 



What, then, is the result of my appeal to the stars which 

 Dr. Huggins's beautiful researches have rendered possible ? We 

 have in the hottest stars a spectrum so regular, so rhythmic, 

 that it seems impossible not to consider it as produced either 

 by the same substances or by substances closely allied. Is it 

 by mere accident that some of the least refrangible lines coincide 

 with those of hydrogen ? Fig. 94 is a copy of Dr. Huggins's 

 diagram, to which reference has been made. At the top is a 

 portion of the solar spectrum in the violet and ultra-violet, and 

 next is the spectrum of the hottest star, a Lyrse. This spectrum, 

 it will be seen, is simpler even than the spectrum of the solar 

 prominences, and not only is there this wonderful simplicity, 

 but an exquisite rhythm by which the distance between 

 the lines gradually increases as we go from one end of the 



