96 LIGHT SCIENCE FOR LEISURE HOURS. 



of less pressure, and a region where they can part more 

 freely with their heat. Thus, precisely as the cumulus- 

 clouds form in our own atmosphere, so would a layer 

 of clouds be formed somewhat low down in the solar 

 atmosphere. But from the upper surface of this layer 

 the vapors of the elements composing the clouds would 

 rise, again to condense at a higher level, much as the 

 light cirrus-clouds in our own atmosphere form at a 

 great height above the layer of cumulus-clouds. 



The great difference between this process and what 

 takes place in our own atmosphere would consist in 

 the fact that whereas the only kind of cloud which can 

 form in our air is a water-cloud, there can be formed in 

 the solar atmosphere clouds of iron, copper, zinc, and 

 other such elements, each element having its own 

 distinct range, so to speak, within the limits of the 

 solar atmosphere. 



Now, with such processes as these going on, we can 

 conceive how rushes of heated gas might from time to' 

 time thrust aside the cloud-layers ; and how where this 

 happened we should occasionally recognize the bright 

 lines corresponding to the more intensely-heated gas, 

 as well as the dark lines corresponding to the deep 

 vapor-masses laid bare by the removal of the photo- 

 sphere. And precisely in this way do the observations 

 recently made by Mr. Lockyer seem alone to be expli- 

 cable. He sees the glowing vapors above the photo- 

 sphere stirred from time to time as by fierce tempests 



