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AIR 



I recollect a summer spent on a New Hampshire farm; and 

 know that an old farmer started his farm hands haying by 

 moonlight at two o'clock in the morning, because the Special 

 Farmer's Weather Forecast of the preceding evening had 

 predicted rain for the following day. His reliance on the 

 weather report was not misplaced, since the storm came with 

 full force at noon. Sailing vessels, yachts, and fishing dories 

 remain within reach of port if the barometer foretells storms. 



82. Isobaric and Isothermal Lines. If a line were drawn 

 through all points on the surface of the earth having an 

 equal barometric pressure at the same time, such a line 

 would be called an isobar. For example, if the height of 

 barometers in different localities is observed at exactly the 

 same time, and if all the cities and towns which have the 



J80 J60 MO 120 100 80 GO 4O 



20 40 60 8< 



Isotherms. 



140 160 l&O 



same pressure are connected by a line, the curved lines will 

 be called isobars. By the aid of these lines the barometric 

 conditions over a large area can be studied. The Weather 

 Bureau at Washington relies greatly on these isobars for 

 statements concerning local and distant weather forecasts, 



