CHAPTER XVII 

 WEATHER MAPS 



Fig. 239 is a weather map of the United States for January 12, 

 1899. Like other weather maps, it shows (1) isobars (full lines) 

 which indicate the distribution of atmospheric pressure; (2) the 



100 loo HO 30 50 80 75' 70" 65 



Fig. 239. Weather map of the United States for January 12, 1899. The full 

 lines are isobars, the broken lines isotherms, and the black circles indi- 

 cate cloudiness. (U. S. Weather Bureau.) 



direction of the winds (shown by arrows) in various parts of the 

 country; (3) the condition of the air with reference to cloudiness, 

 rainfall, snowfall, etc., at all points; and (4) isotherms (broken 

 lines), which indicate the temperature throughout the country. 



283 



