320 BAROMETER. 



the air both cold and dry : the air, there- 

 fore, is both condensed, and without 

 vapour. 



Q. What is the SND SPECIAL RULE in regard 

 to the barometer P 



A. The barometer is lowest of all 

 during a thaw which follows a long frost : 

 it generally falls with SOUTH and WESTERN 

 winds. 



Q. Why does the barometer fall LOWEST of all 

 at the BREAKING UP of a long FROST ? 



A. 1st Because the air (which had 

 been much dried by the frost) absorbs 

 the moisture of the fresh warm current of 

 wind from the south or south-west : and 



2ndly The air (which had been much 

 condensed by the frost) is suddenly 

 expanded by the warm wind which is 

 introduced. 



Q. Why does the barometer fall very low with 

 SOUTH and WEST winds ? 



A. Because SOUTH and WEST winds 

 come heavily laden with vapour; and 

 vaporized air is lighter than dry air. 



Q. What effect has WIND on the mercury ? 



A. All winds make the barometer 



