Why is there but little dew on a cloudy night?
Because the clouds prevent radiation of heat from the earth; hence, the earth and the objects near it, remain too warm to cause any dew.
Why is there a heavy dew on a clear night?
Because there is nothing then to prevent free radiation of heat from the earth; hence, it soon cools so as to cause a heavy dew.
How may dew be prevented from forming on any object?
By placing a cover over that object.
How does a cover prevent the formation of dew?
It prevents the object that is covered from giving off its heat, so that it does not get cool enough to cause a deposit of dew.
Why is there but little dew under trees?
Because trees prevent the free radiation of heat from the objects beneath them; hence, but little dew is formed under trees.