A. White is a very bad absorbent of solar heat; and, therefore, the white tomb-stone remains too cold to thaw the frost congealed upon its surface.
Q. Why is there little or no hoar-frost under shrubs and shadowy trees?
A. 1st—Because the leafy shrubs and trees arrest the process of radiation from the earth: and
2ndly—Shrubs and trees radiate a little heat towards the earth; and, therefore, the ground beneath is never cold enough to congeal the little dew which rests upon it.
Q. What is the cause of that hoar-frost which arises from frozen fog?
A. The thick fog (which invested the earth during the night) is condensed by the cold frost of early morning, and congealed upon every object with which it comes in contact.
CHAPTER XVII.
5.—CONVECTION.
Q. What is meant by the convection of heat?
A. Heat communicated by being carried to another thing or place; as the hot water resting on the bottom of a kettle, carries heat to the water through which it passes. (see p. [246]).