Radiant Heat and Light 153 



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. 



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 



