COMPOUND MICROSCOPE 165 



piefce of wire, and then look at the wire obliquely, the wire seems to be 

 broken at the edges of the glass. Try it, and give the reason. 



5. If you look obliquely downward at a fish on the bottom of a pond, 

 is the fish where it seems to be? Is it nearer you or farther away? 

 Draw a figure to show why. 



6. Why do we see the sun after it has really set, and before it has 

 really risen? 



7. Investigation has shown that forest fires are sometimes caused by 

 glass bottles left by campers; explain. 



8. Do we ever see a rainbow at midday? Explain why. 



9. A mercury vapor electric lamp contains almost no red rays. What 

 effect has this upon the color of objects? 



10. For what reasons can vegetables be raised so much earlier in a 

 box covered with glass (a " cold frame ") than in the open air? 



186. Simple Microscope, or Magnifying Lens. The 

 simple microscope (Fig. 158) consists of a convex lens 

 that will bring light to a focus. The object to be magni- 

 fied (here the arrow a b) is placed 



between this focus and the lens. The 



figure shows that the image (a' b') 



will appear to be farther from the 



lens than the object is, and that it The leng ^tt object ap - 



will be right side up and enlarged. pear lar r g e e v r er b se t it doe8 not 



187. Compound Microscope. The compound micro- 

 scope (Fig. 159) consists of (1) a concave, i. e., hollowed 

 out, mirror to collect and direct light rays; (2) an object 

 lens, or objective ; and (3) an eye-piece. The inside of the 

 microscope tube is black, to prevent light from being re- 

 flected back and forth. 



The object to be magnified (a 6) is fastened in a glass " slide," and 

 is lighted up by rays directed by the mirror. The rays from the object 



