588 Our Surroundings 



brightness or dimness. The light from the lamp falls on a special 

 photographic negative, very sensitive to light, which is fastened 

 to a cylinder revolving at the same speed as the cylinder in the 

 sending apparatus. As the lamp varies in brightness, the exposed 

 negative records dark and light patches corresponding to the dark 

 and light patches on the picture in the sending apparatus. The 

 negative is then developed and a picture is printed from it, which 

 is an almost exact reproduction of the picture in the sending 

 apparatus. 



The process of telephotography is still far from perfect. Pic- 

 tures sent by wire or radio are usually somewhat blurred and 

 can easily be distinguished from ordinary photographs. The next 

 time you look through a newspaper, see if you can find any tele- 

 photographed pictures. 



Television. You sit down at your radio set, turn a knob or 

 switch, twist a dial, and hear the voice of a person who may be 

 hundreds or even thousands of miles away. A wonderful experi- 

 ence, which many of us have every day without stopping to think 

 how really marvelous it is ! Now, thanks to the work of skilled 

 scientists, an even greater wonder is made possible. Not only 

 can we hear the distant broadcaster, but, with the proper appara- 

 tus, we can also see him by a process known as television. The 

 word television means "seeing at a distance." 



The essential parts of a television sending set are a powerful 

 lamp, a scanning disk, and two or more photoelectric cells. The 

 person who is to be "seen" sits in front of the scanning disk, 

 which is a circular piece of metal pierced by a spiral series of 

 holes. Opposite him, beyond the disk, is the powerful lamp. The 

 photoelectric cells are arranged nearby in such a position that any 

 light which falls upon the face of the broadcaster is reflected to 

 them. 



In broadcasting, the scanning disk is whirled rapidly by an 

 electric motor, and the light from the powerful lamp passes 

 through the holes in the disk, falls on the face of the broadcaster, 

 and is reflected to the photoelectric cells. As the first hole comes 

 opposite the lamp, a brilliant beam of light passes through it and 

 sweeps across the top of the broadcaster's face. As the second hole 



