A. The higher the barometer, the greater is the probability of fair weather.
Q. Why is the barometer high in fine weather?
A. Because the air contains but very little vapour. The drier the air, the higher does the mercury of the barometer 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; but when the mercury is in a sinking state, foul weather is near.
Q. Why does the mercury rise 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.