Q. When is dew most copiously distilled?
A. After a hot day in summer or autumn, with the wind in the west.
Q. Why is dew distilled most copiously after a hot day?
A. Because the surface of the earth radiates heat very freely at sunset; and (becoming thus much colder than the air) chills its vapour, and condenses it into dew.
Q. Does not air radiate heat, as well as the earth and its various plants?
A. No. The air never radiates heat, nor is the air itself made hot by the rays of the sun.
Q. How is the air made hot or cold?
A. By convection of hot or cold currents.
Q. What is meant by “convection of hot and cold currents?”
A. The air (which is heated by the surface of the earth) ascends, warming the air through which it passes. Other air (being warmed in a similar way) also ascends, carrying heat; till all the air is made hot.