144 Miracles Ahead! 



or F.M. is used, the "carrier" wave is transmitted from the 

 antenna, varied or "modulated" in time with the variations of 

 the microphone, just as the electric current in the telephone 

 lines varies in time with the disk in the mouthpiece. 



At the "receiver" in our homes (just as at the receiver of 

 a telephone) the process is reversed; the variations on the 

 carrier waves (which are exactly "in time" with the vibra- 

 tions of the microphone back in the studio) affect the cone 

 of the loud-speaker on our radio receiver, and it vibrates in 

 time with those original vibrations and sets up sound waves 

 which repeat the original sound. 



Sending Pictures by Radio 



When a picture is sent by wire, again we have the steps of 

 varying or modulating electric current in time with certain 

 elements in the picture and, at the receiver end, of turning 

 these variations into the picture again. When a picture is sent 

 by radio, we vary or modulate the carrier wave at the trans- 

 mitter in time with certain elements in the picture; at the 

 receiver we "demodulate" the carrier wave, or take these vari- 

 ations from it again and turn them back into the picture. 



To understand the principle of television, examine a pho- 

 tograph in a newspaper through a reading glass. You'll note 

 that the "picture" is made up of a series of dots. The coarser 

 the dots, the less distinct the picture will be. The finer the 

 dots, the clearer the picture will be. 



If you were going to send this picture by radio, you would 

 "scan" the picture with a beam of electrons, beginning at the 

 upper left corner, crossing the picture to the right side, mov- 

 ing down one row of dots and crossing the picture again, and 

 so on until you had "scanned" every row of dots from top to 

 bottom. Now if the dots of the picture could cause electric 

 current to vary, just as the vibrating disk of a microphone, 



