Q. Why can persons in the dark street see into a room (lighted by a candle or lamp)?
A. The pupil of the eye expands greatly, when persons are in the dark; and, therefore, when any one in the dark street looks into a light room, his dilated pupil sees every thing distinctly.
Q. Why does it always freeze on the top of a mountain?
A. Air is heated by the reflection of the earth, and not by the rays of the sun; and, as there is no earth round a mountain-top to reflect heat, therefore, it remains intensely cold.
CHAPTER XVI.
4.—RADIATION.
Q. What is meant by radiation?
A. Radiation means the emission of rays: thus the sun radiates both light and heat; that is, it emits rays of light and heat in all directions.