ISOBARIC AND ISOTHERMAL LINES 



383 



ditions. In this way precautions are taken which annually 

 save millions of dollars and hundreds of lives. 



On a New Hampshire farm, not long ago, an old farmer 

 started his farmhands haying by moonlight at two o'clock 

 in the morning, because the Special Farmers' 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, 



FIG. 253. Barograph. 



yachts, and fishing dories remain within reach of port if the 

 barometer foretells storms. 



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. 

 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, any shift in isobaric lines showing 

 change in atmospheric pressure. 



