2 7 8 



OUR PHYSICAL WORLD 



the telephone receiver to vibrate in exactly the same manner 

 as the diaphragm of the microphone at the sending station. Thus 

 the same receiving set used for receiving the dots and dashes from 

 a discontinuous wave station is used for receiving the programs 

 from the radio telephone broadcasting station (Fig. 129). 



FIG. 129. The operating room of a broadcasting station. (Photo by Sweeny 

 Automotive and Electrical School, Kansas City, Mo.) 



Much more elaborate systems of receiving equipment are 

 commonly used for receiving educational lectures and musical 

 programs from large broadcasting stations. The principle of 

 their operation is identically the same as that of the simpler 

 receiving sets previously described. In addition to the simple 

 receiving circuit of these elaborate assemblies of equipment, 

 there is usually an arrangement of vacuum-valve circuits whereby 

 the incoming signal is very much amplified (Fig. 130). Loud- 



