Guess, by eye-measurement only, the longest and shortest of the three lines marked A A, B B, and C C. When you have done guessing measure, and see how much you are out.
Which is the tallest gentleman of the three appearing in adjoining figure?—Many would imagine the last to be the tallest, and the first the shortest, whereas the reverse is the case—the last is the shortest, and the first the tallest.
It is surprising how the eye can be deceived, when dealing with areas or circles. Place on the table a half-crown and a threepenny-piece; let these be, say, 9 or 10 inches apart, and ask a friend how many of the latter can be placed on the former—with this proviso: the threepenny-pieces must not rest on each other, nor must they overlap the outer rim of the half-crown; they must be fairly within the circumference of the larger coin. Many will answer 6, 5, or 4, others who are more cautious 3. Try for yourself and see how many you can put on, and you are sure to be surprised.
ARE THESE LINES PARALLEL?
The “herring-bone” figure here illustrated is yet another proof that our eyes are faulty. The horizontal lines appear to slant in the direction in which the short intersecting lines are falling, and would give one the idea that they would meet if continued, whereas really they are parallel. The illusion is more striking if you tilt the leaf up.