THE HUMAN EYE 121 



make the image larger than the object, it would be impossible 

 for the lens to assist the watchmaker in locating the small 

 particles of dust which clog the 

 wheels of the watch. If it 

 were not for the opposite fact 

 that a lens can be held at 

 such a distance from the object 

 as to make an image smaller FIG. 77. - The lens is placed in such a 

 than the object, it would be im- fg-g * ab "< " 

 possible to have a photograph 



of a tall tree or building unless the photograph were as large 

 as the tree itself. When a photographer takes a photograph 

 of a person or a tree, he moves his camera until the image 

 formed by the lens is of the desired size. By bringing the 

 camera (really the lens of the camera) near, we obtain a large- 

 sized photograph ; by increasing the distance between the 

 camera and the object, a smaller photograph is obtained. 

 The mountain top may be so far distant that in the photo- 

 graph it will not appear to be greater than a small stone. 



Many familiar illustrations of lenses, or curved refracting 

 surfaces, and their work, are known to all of us. Fish globes 

 magnify the fish that swim within. Bottles can be so shaped 

 that they make the olives, pickles, and peaches that they 

 contain appear larger than they really are. The fruit in 

 bottles frequently seems too large to have gone through the 

 neck of the bottle. The deception is due to refraction, and 

 the material and shape of the bottle furnish a sufficient expla- 

 nation. 



By using combinations of two or more lenses of various 

 kinds, it is possible to have an image of almost any desired 

 size, and in practically any desired position. 



116. The Human Eye. In Section 114, we obtained on a 

 movable screen, by means of a simple lens, an image of a 



