Q. Why is it dangerous to sleep in a room which contains living plants?
A. Because they exhale carbon in the dark in the form of carbonic acid gas, which is destructive to animal life.
Q. Why are some things (like glass) transparent?
A. In transparent bodies (like glass) all the rays of light emerge on the opposite side.
Q. Why are some things shining and splendid?
A. Those objects which reflect the most rays are the most splendid; and those which absorb them most, are dull.
Q. Why are deserts so dazzling in summer time?
A. Because each separate grain of sand reflects the rays of the sun like a mirror.
Q. If you move a stick (burnt at one end) round pretty briskly, it seems to make a circle of fire,—Why is this?
A. Because the eye retains the image of any bright object, after the object itself is withdrawn; and as the spark of the stick returns before the image has faded from the eye, therefore, it seems to form a complete circle.