Fig. 79. A section of the eye.
The important point in this experiment is for you to see that if the lens is nearer to the image on the paper than it is to the candle, the image is smaller than the candle. That is why a photograph is usually smaller than the thing photographed; it would be impossible to take a picture of a house or a mountain if the lens in the camera gave a magnified image.
[4]Your eye is a small camera. It has a lens in the front; it is lined with black; and at the back there is a sensitive part on which the picture is formed. This sensitive part of the eye is called the retina. It is in the back part of your eyeball and is made of many very sensitive nerve endings. When the light strikes these nerve endings, it sends an impulse through the nerves to the back part of the brain; then you know that the image is formed. And, of course, since your eyeball is small and many of the things you see are large, the image on the retina must be much smaller than the object itself, and this is because the lens is so much nearer to the retina than it is to the object.
[Footnote 4]: The following explanation may be omitted by any children who are not interested in it. Let such children skip to the foot of page [156].
Fig. 80. How an image is formed on the retina of the eye.
Fig. 81. A simpler diagram showing how an image is formed in the eye.
