Page:Popular Science Monthly Volume 28.djvu/189

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PSM V28 D189 Lense of the eye interpreting two simultaneous light sources.jpg
Diagram 4.

a shock, the sensation of a point of light is produced. As shown in the diagram, just one rod is agitated by each set of waves, so that the eye sees in this case two distinct points of light, the brilliancy of each depending upon the intensity of the agitation, A third vibrating molecule in another star would be seen by the eye in the same way, and so on indefinitely.

As the color of light depends merely on the wave-length, we can now understand how the eye sees the constellations in their true configurations and colors; and, as reflected light has the same effect on the eye as that coming directly from self-luminous points, it is plain that the eye must see the form and color of all luminous objects, each individual point of each object forming its own focus on one of these sensitive rods of the retina.

Can any mechanism be more simple and beautiful than that of vision? The more it is studied the more admirable it seems, and we are in a still better position to appreciate the elegance of the mechanism which enables the lens of the eye to form a perfect image of distant objects upon the sensitive retina, when we take into consideration the fact that, were the waves of light not so excessively minute, distinct vision would be utterly impossible.

It is only because the light-waves are so much smaller than the aperture of any lens, such as the lens of the eye, that they run to a focal point, instead of spreading out in all directions, as do the waves of sound which enable us to hear round a corner. The effect of decreasing the aperture of the lens of the eye to a size comparable with that of the light-waves (which would in effect be the same as increasing the length of the light-waves to a size comparable with that of the eye) can easily be shown thus: