416 THE CHEMISTRY OF THE SUN. [CHAP. 



When we watch the growth of such a prominence it expands 

 from below, close to the photosphere. First the prominence 

 is of small height, then it gets higher and generally broader, and 

 after a certain time we may see a kind of cloud formed at the 

 top of it. 



It happens very rarely indeed that any very rapid vertical 

 motion is indicated in such prominences as these. 



Fio. 123. Metallic prominence, Young. Rate of ascent 400,000 miles an hour. 



(4) Metallic prominences. The most intense degree of action 

 is observed in what are termed metallic prominences, for the 

 reason that they are known to include other substances besides 

 hydrogen. 



These are the most magnificent manifestation of energy which 



photosphere. But so rapid was the cooling which attended this rapid expansion, 

 that in two minutes after it was last measured it had completely vanished. 

 L' 'Astronomic, vol. iv. p. 441. 



