182 THE STORY-BOOK OF SCIENCE 



you will see a cloud begin with being white, then 

 turn scarlet, then shine like a pile of embers, or like 

 a lake of melted gold, and finally become dull and 

 turn gray or black, according as the sun's rays 

 strike it less and less. All that is a matter of illu- 

 mination by the sun. In reality, clouds, however 

 splendid in appearance, are formed of a damp vapor 

 like that of fog. We can assure ourselves of this 

 by a near approach. ' ' 



"People can then mount as high as the clouds, 

 Uncle !" Emile asked. 



' i Certainly. All one needs is a pair of legs stout 

 enough to climb to the top of a mountain. Often 

 then clouds are under one's feet." 



"And you have seen clouds underneath you?" 



"Sometimes." 



"That must be a very beautiful sight." 



' ' So beautiful that words cannot express it. But 

 it is not exactly a pleasure if the clouds mount and 

 envelop you. You can be very much embarrassed 

 by the obscurity of the fog alone. You lose your 

 way; you become confused, without suspecting any 

 danger in the most dangerous places, at the risk of 

 falling into some abyss ; you lose sight of the guides, 

 who alone know the way and could save you from a 

 false step. No, all is not roses up among the clouds. 

 You will perhaps learn that some day to your cost. 

 Meanwhile let us transport ourselves in imagination 

 to the top of a cloud-capped mountain. If circum- 

 stances are favorable, here is what we shall see : 



"Above our heads the sky, perfectly clear, pre- 

 sents no unusual appearance; the sun shines there 



