330 



SCIENCE OF HOME AND COMMUNITY 



together, because the 

 action of the decoherer 

 does not allow a dash 

 to be made. 



Tuning. After it 

 had been found pos- 

 sible to send messages 

 by wireless over long 

 distances, one of the 

 first difficulties that 

 arose was how to do 

 this in such a way 

 that other instruments 

 than the one for which 

 it was intended should 

 not receive the mes- 

 sage. Many experi- 

 ments have been tried 

 and now this privacy 

 is insured by a system 

 of tuning, as it is 

 called. This is done by 

 regulating the wave 

 length that is given 

 out by a certain send- 

 ing apparatus, so that 

 it can be received only 

 by an apparatus which 

 is tuned to correspond 

 to the same wave 

 _,_ length. But in order 



<=r ar to insure secrecy, codes 



tic. 136. Wireless receiving apparatus. , . . ., . 



are used which can be 



understood only by those who know the key to the code. A 

 single word may stand for a whole sentence. 



