  Illusions of the eye are numberless, and afford a wide field for experiment. For example, if you ask any one wearing a silk high hat, to what height he thinks his hat would reach if placed on the ground against the wall or door. Nine times out of ten the mark of the height guessed Again, represents two triangles. Ask which is the one whose center is the better indicated. Every one will say, “triangle A.” Well, every one will be wrong, it is B. Take a pair of compasses and you will easily prove it. The same occurs with the above figure. The two parallelograms, A B, are absolutely equal, and yet A appears to be larger than B. The two lines, A and B are both of equal length; yet B seems a third longer than A. The sides, AB, CD, BD of the middle figure, BE, AM, EM, etc., are equal, yet it seems to the eye that the surface, A B E M, is longer than the square A B C D. There is another deception the eye is liable to. On a sheet of paper trace several circles, having the same center. Place the sheet on your thumb and turn it horizontally, it will then seem to you as if the rounds turned, though you watch with the utmost attention, the illusion will be complete. In order to terminate this series, which can be varied infinitely, we will, in our turn, ask you this question: Which is the tallest man of the three personages appearing in the adjoining figure? Is it the first, the last, or the middle one? Try to find out without any instrument of course, simply However, measure with a pair of compasses, and the illusion will at once disappear. The draughtsman was not mistaken; the first is the tallest, and the two others go diminishing in height. This terminates our experiments on optical illusions and you will now enter upon another field of knowledge altogether. |
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