Color Illusions
Most of us know the result of turning a series of circles (as in [Fig. 11]) horizontally with the eye. The circles appear to revolve rapidly round their center, and in different directions. This is solely because the eyes become confused, giving one more proof, were it needed, that they are no more infallible than anything else on this wide earth.
Some very interesting experiments in color illusions can be made. So cunning is the deception played upon us by our eyes, it is extremely difficult to believe that some of the tints we see in the experiments are but imaginary.
Fig. 11.—Revolving circles.
Fig. 12.—The color top.
In [Fig. 12] you see a top which can be constructed of cardboard in this way. Take a postcard and cut a circle, upon which you draw a diameter as A B. Black the part A C B with India ink, and divide the other half into four equal portions by lightly penciling the radii G E, G D, and G F. Now, still using your India ink, make arcs in these four divisions in the same way as is shown in the figure.
Fig. 13.—To make black print red.
Having done this carefully and rubbed out the pencil radii when the ink has dried, put a pin through the center G from the back, so that the card can easily revolve whilst the pin-head prevents it from falling off. Your color top is now ready. Make it turn rapidly upon the pin; look closely at the card and what do you see? The inner circles become red and the outer ones blue! And yet you know perfectly well that the only colors really upon the card are black and white!
You can make another top, after a similar fashion. Cut your postcard as before, making one half of it black. Now, out of the white side, cut a segment with an angle of 45 degrees, leaving a little piece near the center as shown in [Fig. 13]. This piece you have left has nothing to do with the effect, but is simply to make the top revolve better.
Take an ordinary book, of which the printing is presumably black, and revolve the top upon the pin at the rate of about five turns a second (a sharp twitch with the finger will do this perfectly well). If you look at the printing now you will find the letters are colored red, as though the book had been printed in red ink!
In both these experiments the alternation of black and white has not only confused the eye, but has deceived it into seeing colors which do not really exist.
So we have shown very conclusively that the old proverb, “all is not gold that glitters,” can be applied to even the plainest of black and white; and, as the poet remarks, “things are not what they seem.”
Therefore, when people wish to impress you with the evidence of their own eyes and clinch an argument by stating that they saw such and such a thing and cannot be wrong, show some of these optical illusions and demand a better proof of what they affirm, very courteously assuring the dogmatist that the best of eyes are liable to make mistakes.