146 Miracles Ahead! 



with the varying number of electrons which reach it. When 

 the original variations on the carrier wave are fed to the elec- 

 tron gun in the receiver mechanism, the number of electrons 

 emitted from it varies "in time" with the variations in the 

 reactions of the electric black dots and white spaces of the 

 original picture, and the picture is repeated on the receiver 

 screen, a dot at a time, just as it was picked up from the 

 transmitter screen. 



Why do we see a complete picture and not a dot at a time? 

 Because the electron gun scans the picture so rapidly, going 

 from left to right and from top to bottom so fast, that it makes 

 a complete picture in one-thirtieth of a second! 



Most of us are familiar with the principle of the motion 

 picture. We have looked at a "strip" of film, seeing picture 

 after picture with changes so slight that it is hard to detect 

 these changes unless we look at quite a long strip of film. 

 "Movies," as we know, are possible because the human eye 

 cannot see fast enough to distinguish the different pictures 

 when they are flashed on a screen at a speed of more than 

 sixteen different pictures, or "frames," a second. Therefore 

 we see, not different pictures, but a continuous flow of action. 



Television, too, flashes complete pictures, or "frames," on 

 the screen of a receiver too fast for us to distinguish the dif- 

 ferent pictures. It flashes thirty "frames" a second, although 

 it must flash each frame a dot at a time! If the picture were 

 four hundred dots high and five hundred dots wide, the beam 

 of electrons scanning the picture would cause two hundred 

 thousand variations in the electric current in scanning the 

 picture once. In sending moving pictures by television, to 

 send thirty complete frames a second the electronic beam 

 would vary the current six million times a second! 



There we come to one great difference between television 

 broadcasting and our everyday sound broadcasting. We do 



