Fig. 82. A diagram showing how a reading glass causes things to look larger by making the image on the retina larger.
Fig. 83. Diagram showing how a reading glass enlarges the image on the retina. More lines are drawn in than in Figure 82.
You can understand magnification best by looking at Figures 80, 81, 82, and 83.
In Figure 80 there are a candle flame, the lens of an eye, and the retina on which the image is being formed.
Figure 81 is the same as Figure 80, with all the lines left out except the outside ones that go to the lens. It is shown in this way merely for the sake of simplicity. All the lines really belong in this diagram as in the first. In both diagrams the size of the image on the retina is the distance between the point where the top line touches it and the point where the bottom line touches it.
In order to make anything look larger, we must make the image on the retina larger. A magnifying glass, or convex lens, if put in the right place, will do this. In the next diagram, Figure 82, we shall include the magnifying glass, leaving out all lines except the two outside ones shown in Figure 81.
You will notice that the magnifying glass starts to bend the lines together, and that the lens in the eye bends them farther together; so they cross sooner, and the image is larger. Figure 83 shows more of the lines drawn in.
