CLOUDS AND RIVERS, ICE AND GLACIERS. /> 



experiment may be made more striking, but not more 

 instructive, than with the kettle. 



12. Look to your bedroom windows when the weather 

 is very cold outside ; they sometimes stream with water 

 derived from the condensation of the aqueous vapour 

 from your own lungs. The windows of railway carriages 

 in winter show this condensation in a striking manner. 

 Pour cold water into a dry drinking-glass on a summer's 

 day : the outside surface of the glass becomes instantly 

 dimmed by the precipitation of moisture. On a warm 

 day you notice no vapour in front of your mouth, but 

 on a cold day you form there a little cloud derived 

 from the condensation of the aqueous vapour from the 

 lungs. 



13. You may notice in a ball-room that as long as the 

 door and windows are kept closed, and the room remains 

 hot, the air remains clear; but when the doors or windows 

 are opened a dimness is visible, caused by the precipi- 

 tation to fog of the aqueous vapour of the ball-room. 

 If the weather be intensely cold the entrance of fresh 

 air may even cause snow to fall. This has been ob- 

 served in Russian ball-rooms ; and also in the subterra- 

 nean stables at Erzeroom, w T hen the doors are opened 

 and the cold morning air is permitted to enter. 



14. Even on the driest day this vapour is nevet 

 absent from our atmosphere. The vapour diffused 

 through the air of this room may be congealed' to hoar 

 frost in your presence. This is done by filling a 



