324 BAROMETER. 



A. Because the air contains but very 

 little vapour. The drier the air, the 

 higher does the mercury of the barom- 

 eter rise. 



Q. What is the 9TH SPECIAL RULE in 

 regard to the barometer ? 



A. When the mercury is in a rising 

 state, fine weather is at hand j but when 

 the mercury is in a sinking state, foul 

 weather is near. 



Q Why does the mercury KISE at the 

 approach of FINE weather ? 



A. Because the air is becoming 

 more dry, and therefore its pressure is 

 greater. 



Q. Why does the mercury SINK at the 

 approach of FOUL weather ? 



A. Because the air is laden with 

 vapour, or disturbed by wind. 



Q. Why does VAPOUR in the air make the 

 mercury SINK ? 



A. Because vaporized air is lighter 

 than dry air, and therefore its pressure 

 is less on the mercury of the barometer. 



Q. What is the 10TH SPECIAL KTJLE in 

 regard to the barometer ? 



