Mingling of Molecules 



285 



before it gets to him. Then there may be a shower of 

 rain when he has predicted fair weather. Or some- 

 times the air that has been rising to the west, and which 

 has made him predict bad weather, may stop rising; 

 the storm may be over before it reaches his station. 

 Then his prediction of bad weather is wrong. Or some- 

 times the storm unexpectedly changes its path. There 

 are many ways in which a weather prophecy may go 

 wrong; and then we blame the weather man. We are 

 likely to remember the times that his prophecy is mis- 

 taken and to forget the many, many times when it is 

 right. 



How snow is formed. The difference between the 

 ways in which snow and rain are formed is very slight. 



FIG. 156. An aneroid barometer is more convenient than one made with mer- 

 cury. The walls are forced in or spring back out according to the pressure of 

 the air. This movement of the walls forces the hand around. 



