Q. What is dew?
A. Dew is the vapour of the air condensed, by coming in contact with bodies colder than itself.
Q. Why is the ground sometimes covered with dew?
A. The earth is more heated by solar rays than the air, during the day; but at night, the earth parts with more heat than the air, and becomes (in consequence) 5 or 10 degrees colder.
Q. How does the earth being colder than the air account for the deposition of dew?
A. As soon as the air touches the cold earth, its warm vapour is chilled, and condensed into dew.
Q. Why is the surface of the ground colder in a fine clear night, than in a cloudy one?
A. On a fine clear star-light night, heat radiates from the earth freely, and is lost in open space: but on a cloudy night, the clouds arrest the process of radiation.
Q. Why is dew deposited only on a fine clear night?