Q. Why does a river always appear more shallow than it really is?
A. Because the light of the bottom of the river is refracted as it emerges out of the water: and (as a stick is not so long when it is bent, as it is when it is straight) so the river seems less deep than it really is.
Q. How much deeper is a river than it seems to be?
A. One-third. If, therefore, a river seems only 4 feet deep, it is really 6 feet deep.
N. B. Many boys get out of their depth in bathing, in consequence of this deception. Remember, a river is always one-third deeper than it appears to be:—thus, if a river seems to be 4 feet deep, it is in reality 6 feet deep, and so on.
Q. Why do fishes always seem to be nearer the surface of a river than they really are?
A. Because the rays of light from the fish are refracted as they emerge from the eye: and (as a bent stick is not so far from end to end as a straight one) so the fishes appear nearer our eye than they really are.
Q. Why are some persons near-sighted?
A. Because the COR´NEA of their eye is so prominent, that the image of distant objects is reflected before it reaches the ret’ina; and, therefore, is not distinctly seen.
N.B. The cor´nea shields the crystalline lens, and is more or less convex according to the lens which it covers.