BOYS' OWN COLUMN.

Auckland Star, Volume LX, Issue 224, 21 September 1929, Page 2 (Supplement)

BOYS' OWN COLUMN.

WHY HAVE WE TWO EYES? THE PRINCIPLE OF THE STEREOSCOPE. Dear Boys,— Quite often one hears the expression "A chap needs two pairs of eyes," but very seldom one stops to think and ask the question above. Now I wondered recently why we had two eyes, so I delved deep into the "Children's Encyclopaedia," and this is what I found there: The possession of two "eyes enables us to form a judgment as to the bulk of an object, or as to the depth of a depression, or as to the real position of one object in relation to another. As our eyes are set from about two to two and a-half inches apart from each other—measuring centre to centre—they each get a slightly different view of the object looked at. To fully realise this, let us tako a round pot bearing a printed label half turned away from our eyes. If wo do this and look at the pot, closing each eye alternately, we shall find! ihat cite eye can read more of the label than the other. The right eye sees more of the right side of the pot, and the left eye sees more of the left side; so that with our two eyes we see more than half tiic pot. It is this looking round the sides of an object which gives us the impression of solidity. An artist cannot give us this impression, no matter how clever he is. But a photographer can do it by taking with a double camera—the lenses of which are set apart like the eyes—two pictures of the same object. These two pictures are set side by side in an instrument called the stereoscope, and we look at them with our two eyes, the right seeing the right-hand picture only, and the left seeing the left-hand picture only. As a result we see solidity, one object standing out from another as if we were looking at real things. Thus, the two eyes are not for ornament alone t but for real use. Why it is that the ,brain is able to combine the two pictures as it does we do not know.

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