Q. Why is a sudden change from cold to hot followed by rain?
A. Because the air is quickly saturated with moisture; and as soon as night comes on, the temperature is lowered again, and some of the abundant moisture falls in rain.
Q. Why is the air quickly saturated with moisture, when heat succeeds rapidly from cold?
A. Because the evaporation (which was checked by the cold) is carried on very rapidly, in consequence of the diminished pressure of the air.
(N. B. The less the pressure of the air, the more rapidly it evaporates moisture.)
Q. When does the barometer vary most?
A. In winter time.
Q. Why does the barometer vary more in winter than in summer time?
A. Because the difference of temperature between the torrid and temperate zones is so great, that the state of the air is perpetually disturbed by their mixing together.
Q. When does the barometer vary least?