36 GENERAL SCIENCE 



of ice crystals from the atmosphere. The air has cooled below 

 freezing. 



A sudden jar turns a supercooled liquid instantly to a solid; and 

 thus it happens that, in cold weather, raindrops or fog particles 

 turn to ice on coming in contact with trees, telegraph wires, and the 

 like, giving us the interesting spectacle of the " ice storm." 



Snow. When condensation occurs at a temperature below freez- 

 ing the vapor will crystallize and form snowflakes or ice needles 

 of varied forms. In milder weather, when snow falls into a warm 

 stratum of air, it partly melts and reaches the ground as sleet or 

 slush. 



Sometimes during our summers snow forms in the upper part 



FIG. 25. Snow-crystals. 



of a thunder stormcloud, but melts and changes into rain before it 



reaches the earth. 



To give an idea of the amount of water that falls on an acre of 



ground, the following will be of interest: 



0.01 inch of rain equals 62,726 cubic inches or 1.1 tons 

 0.05 312,636 5.6 



0.10 627,264 11.3 



1.00 6,272,640 113.0 



2.00 12,545,280 226.0 



5.00 31,363,200 565.0 



