116 



HOW WE LIGHT OUR HOMES 



Courtesy Eastman Kodak Co. 



FIG 181. MOTION PICTURE CAMERA AND PROJECTION MACHINE FOR HOME USE 



Courtesy Eastman Kodak Co. 



FIG. 182. NEGATIVE AND 

 POSITIVE "MOVIE" FILMS 



film is run through a motion- 

 picture projector while light 

 passes through the film to a 

 white screen, upon which 

 images of the original ob- 

 jects photographed are pro- 

 duced. 



It is interesting to know 

 that what we speak of as mo- 

 tion pictures are in reality a 

 series of still pictures. By cer- 

 tain mechanical arrange- 

 ments in a motion picture 

 projector one frame of the 

 film is projected upon the 

 screen at a time, each frame 

 remaining stationary for 

 about % 2 of a second. While 

 a new frame is being moved 

 into place a shutter covers 

 the film. We do not observe 

 any darkness on the screen 

 during this time because of 

 what is known as "persist- 

 ence of vision." The retina of 

 the eye holds an image a 

 short while after the light 

 producing the image no 

 longer enters the eye. The 

 appearance of successive pic- 



tures on the screen is so timed that the images formed 

 on the retina merge into one another and the brain 

 interprets them as if they were continuous. 



What are some of the other optical instruments im- 

 portant to man? The microscope and telescope 

 especially are being used daily by men of science to 

 discover new information about our universe. 



The microscope is used to study tiny objects that 

 the human eye is unable to see alone. If a compound 

 microscope is available in your school, examine it and 

 get acquainted with the world of little things by view- 

 ing some of them through it. The simple compound 

 microscope consists primarily of two convex lenses so 

 arranged that one lens magnifies the image which the 

 other one makes. In this way the image of a tiny ob- 

 ject may be enlarged hundreds of times before it 

 strikes the retina of the eye. 



The telescope is used to study heavenly bodies such 

 as stars and planets which are large but because of 

 their great distances from us cannot be seen clearly 

 by the naked eye. The refracting telescope consists es- 

 sentially of a long hollow tube with a convex lens at 

 each end. The large lens at the end of the telescope 

 pointing toward the heavenly body collects the light 

 and forms an image of the body in the hollow tube. 

 The lens at the end we look through magnifies the 

 image formed in the tube many times, depending upon 

 the nature of the lens used. There is another kind of 

 telescope called the reflecting telescope, which is made 

 of a combination of mirrors and lenses. 



