405. What benefit results from this arrangement?
In cultivated lands, where moisture is required, it is induced by the very necessity which demands it; while in rocky and barren places, where it would be of no good, dew does not form.
406. Why does little dew form at the base of hedges and walls, and around the trunks of trees?
Because those bodies in some degree counteract the radiation of heat from the earth; and they also radiate heat from their own substances.
407. Why do heavy morning dews and mists usually come together?
Because they both have their origin in the humidity of the atmosphere. The temperature of the earth having fallen, dew has been deposited; but, at the same time, the condensation of the vapour in the air has formed a screen over the surface of the earth, which has checked the further radiation of heat, and, consequently, the further formation of dew. The sun rises, therefore, upon an atmosphere charged with visible vapour at the earth's surface, and his first sloping rays, having little power to warm the atmosphere, the mist continues visible for some time.
408. What effect have winds upon the formation of dew?
Winds, generally, and especially when rapid, prevent the formation of dew. But those winds that are moist, and contribute to the formation of clouds, indirectly aid the formation of dew through the formation of clouds, and also by the moisture they impart to the air.
"And Gideon said unto God, * * * Let it now be dry only upon the fleece, and upon all the ground let there be dew."