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The images in the eye’s dark chamber.
But I have not yet told you how you see. It is done in this way. The light that goes in through the pupil makes an image or picture there of every thing that is before the eye. It makes the image on a very thin sheet spread out on the back part of the dark chamber where the jelly is; it is just as light makes images of things in a looking-glass, or in the smooth, still water; the only difference is, that the image or picture in the eye is very small. When you see a tree pictured in the still water, the picture is as large as the tree itself; but the picture that the light makes of the tree in that dark chamber of your eye is very small. The picture in your eye of a whole landscape, with all its trees, houses, hills, etc., does not cover over a space larger than a ten cent piece.
But how does the mind in the brain know any thing about these pictures? It knows about them by means of a nerve, that goes from the brain to the eye, and is spread out where the pictures or images are made. It would do no good to have the pictures made in the eye, if the nerve could not tell the mind about them. The eye might be perfect, and yet there might not be any seeing. It is as necessary to have the nerve in good order as it is the eye itself. It is not your eye that sees; it is your mind, and in seeing it uses both the nerve and the eye.
Why we have two eyes.
You have two eyes. When you look at one thing, say a house, there is a picture of the house in both eyes. The two nerves tell the mind in the brain about the two pictures. How is this? Why does not the mind see two houses? It is because the pictures in the two eyes are exactly alike, and both nerves, therefore, tell exactly the same story; if they did not, then the mind would see two houses; that is, it would see double, as it is called. You can see double by pressing one eye sidewise while you let the other go free.
The eyes of insects.
The eyes of insects are very curious. You remember what I told you about compound flowers. Now, as in a compound flower there are a great many flowers together, so it is with the eyes of insects. The eye of a common fly is made up of thousands of eyes; so, when he looks at any thing, there are thousands of very little images of it made by the light in these eyes, and the nerves tell the fly’s mind, in his little brain, about them. These eyes are so exceedingly small that you can not see them without a microscope. How fine, then, must be the nerves that go from them to the fly’s brain! Your eye is a very wonderful instrument, but God has put thousands of them just as wonderful into the head of the fly that buzzes about you. It is as easy for him to make little eyes as large ones, and he can make a multitude as easily as one.
Questions.—By what senses does the mind learn the most? What is the white of the eye? What is it filled with? What is there in the front part of the eye? What is said about the dark chamber of the eyeball? What is just inside of the front window of the eye? What is the pupil of the eye? What is the iris? How is it arranged? What is said of its color? What is its chief use? Tell about this. What is said about its being made nicely? What is said about the shape of its opening in different animals? What is said about the cat’s pupil in different lights? Tell about the images made in the eye. What is said about the nerve of the eye? How is it that, with two eyes, you do not see double? Why do you have two eyes? What is said about the eyes of insects?