Because they turn away from the persons in the room rays of heat which would otherwise make the warmth excessive.
218. Why are white and light articles of clothing cool?
Because they reflect the rays of heat.
White, as a colour, is also a bad absorber and conductor.
219. Why is the air often found excessively hot in chalk districts?
Because the soil reflects upon objects near to it the heat of the solar rays.
220. How does the heat of the sun's rays ultimately become diffused?
It is first absorbed by the earth. Generally speaking, the earth absorbs heat by day, and radiates it by night. In this way an equilibrium of temperature is maintained, which we should not otherwise have the advantage of.
221. Does not the air derive its heat directly from the sun's rays?
Only partially. It is estimated that the air absorbs only one-third of the caloric of the sun's rays—that is to say, that a ray of solar heat, entering our atmosphere at its most attenuated limit (a height supposed to be about fifty miles), would, in passing through the atmosphere to the earth, part with only one-third of its calorific element.