6 THE POEMS OF WATER IN 



tressel with a mixture of pounded ice and salt, which 

 is colder than the ice itself, and which, therefore, con- 

 denses and freezes the aqueous vapour. The surface 

 of the vessel is finally coated with a frozen fur, so 

 thick that it may be scraped away and formed into a 

 snow-ball. 



15. To produce the cloud, in the case of the loco- 

 motive and the kettle, heat is necessary. By heating 

 the water we first convert it into steam, and then by 

 chilling the steam we convert it into cloud. Is there 

 any fire in nature which produces the clouds of our 

 atmosphere ? There is : the fire of the sun. 



16. Thus, by tracing backward, without any break in 

 the chain of occurrences, our river from its end to its 

 veal beginnings, we come at length to the sun. 



§2. 



17. There are, however, rivers which have sources 

 somewhat different from those just mentioned. They 

 do not begin by driblets on a hill side, nor can they be 

 traced to a spring. Go, for example, to the mouth of 

 the river Eh one, and trace it backwards to Lyons, where 

 it turns to the east. Bending round by Chambery, you 

 come at length to the Lake of Geneva, from which the 

 river rushes, and which you might be disposed to regard 

 as the source of the Ehone. But go to the head of the 

 lake, and you find that the Ehone there enters it, that 

 the lake is in fact a kind of expansion of the river. 



