CLOUDS AND RIVERS, ICE AND GLACIERS. 3 



soon assure yourself that such springs are also fed by 

 rain, which has percolated through the rocks or soil, 

 and which, through some orifice that it has found or 

 formed, comes to the light of day. 



6. But we cannot end here. Whence comes the rain 

 which forms the mountain streams ? Observation 

 enables you to answer the question. Rain does not 

 come from a clear sky. It comes from clouds. But 

 what are clouds ? Is there nothing you are acquainted 

 with which they resemble? You discover at once a 

 likeness between them and the condensed steam of a 

 locomotive. At every puff of the engine a cloud is pro- 

 jected into the air. Watch the cloud sharply : you 

 notice that it first forms at a little distance from the 

 top of the funnel. Give close attention and you will 

 sometimes see a perfectly clear space between the 

 funnel and the cloud. Through that clear space the 

 thing which makes the cloud must pass. What, then, 

 is this thing which at one moment is transparent and 

 invisible, and at the next moment visible as a dense 

 opaque cloud ? 



7. It is the steam or vapour of water from the boiler. 

 Within the boiler this steam is transparent and in- 

 visible ; but to keep it in this invisible state a heat 

 would be required as great as that within the boiler. 

 When the vapour mingles with the cold air above the 

 hot funnel it ceases to be vapour. Every bit of steam 

 shrinks, when chilled, to a much more minute particle of 



