FIG. 146. Diagram of a com- 

 pound microscope. An object 

 represented by the small arrow 

 at the bottom of the figure is so 

 placed that rays of light leaving 

 it are brought to a focus at ab 

 after passing through the object 

 lens or objective, there forming 

 an inverted image. The rays 

 pass on through the eye lens or 

 eyepiece, diverging less as they 

 pass, and the eye seems to see the 

 magnified virtual image at a'b'. 



OUR PHYSICAL WORLD 



You may make lenses for yourself 

 in either one of two ways that will 

 serve for the time being. First, good- 

 sized lenses may be made from two 

 watch crystals of the same size. Smear 

 their edges with vaseline. Immerse 

 them in water, and bring them edge 

 to edge so that the space between 

 them is filled with water. Be careful 

 not to include air bubbles. Hold the 

 two firmly together between the thumb 

 and fingers of the left hand, lift them 

 out of the water with their contained 

 water, wipe the edges dry and bind 

 them together with a strip of surgeon's 

 adhesive tape as you would passe-par- 

 tout a picture. The tape may be pur- 

 chased at any drugstore, and the i-inch 

 width is best. If the water runs out 

 from between the watch crystals and 

 air leaks in during this process, try it 

 again. It will do no harm if a small 

 bubble of air gets in, but it should 

 not occupy more than one-fifth or one- 

 sixth of the interior. Such a lens will 

 work well as a magnifying glass. 



A second method of making a small 

 lens is as follows : Take a circular cover 

 glass such as is used in the prepara- 

 tion of microscopic mounts. Hold it 

 in a pair of spring forceps such as 

 the bacteriologist uses, and drop on 

 to it some liquid glass or thick Can- 

 ada balsam. Heap up as much as 

 it will hold without running off, then 



