124 



GENERAL SCIENCE 



the water in it, the weight of the dried air remaining is 

 found to be less than what the weight of a cubic foot of dry 

 air at that temperature should be. Evidently the decrease 

 in density of air to which water vapor is added results from 

 the replacement of some air by water vapor whose density 

 is only about five-eighths (.62) as great as that of dry air. 

 In its change from the liquid to the gaseous state water 

 increases in volume about sixteen hundred fold. 



FIG. 46. In changing from a liquid to a vapor water expands about sixteen 

 hundred fold. (Tower, Smith & Turton.) 



As a rule the winds that spring up at times of great 

 conflagrations blow in one direction only, becoming often- 

 times a gale in violence. To account for this it may be 

 supposed that the atmospheric pressure is greater at a 

 place in some one direction from the ascending warmed air, 

 and that the inrush from that side is more marked. 

 Gradually the air current or wind from that direction 

 becomes dominant, supplying the volume of air of the as- 

 cending current so completely that any movement of air 

 inward from other directions is not noticeable. 



This condition of atmospheric movement as a result of 



