

Applied Science 839 



With waves as regular as any electric current in a wire modulation 

 becomes possible and conforms with the inflections of the human 

 voice. The waves sent out, therefore, are modified in strength by 

 the speaking voice, and it is these modified waves that reach the 

 receiving station, to operate on the receiving telephone as in the 

 case of ordinary wire transmission. The chief difficulty, in prac- 

 tice, is in the construction of the telephone transmitter, for it has to 

 pass a much larger current than is used in wire telephones. The 

 ordinary transmitter would become overheated and useless. But 

 there are various devices for overcoming this difficulty, such as 

 combining a number of transmitters and keeping them cooled by 

 water. 



As Sir Oliver Lodge says, wireless telephony is a far more 

 astonishing feat than the transmission of coarse signals like the 

 dot and dash of telegraphy, the sending of impulses across space 

 by a mechanical relay. He says : 



But no mechanical relay could follow the variations of 

 quality in human voice ; no agency short of the electron would 

 be quick and docile enough. But with their aid the feat was 

 accomplished, and the electric waves which acted as the in- 

 termediary could travel a thousand miles or more before 

 being received and once again transmitted. . . . How could 

 the human ear or any instrument follow vibrations of millions 

 a second? It could not. Only the electron could do that. 

 If in addition to the oscillations coming from a distant station 

 they set up home oscillations, in a small subsidiary vacuum 

 tube, of nearly the same frequency if the incoming waves 

 vibrated a million times, for instance, while their local 

 arrangement vibrated a million plus 500 what would hap- 

 pen? They would "beat." They would give 500 beats a 

 second, and that was a musical note. To that they could 

 listen, and upon that the variations of intensity could be 

 superposed. 



That was not the first plan adopted. The first plan was 

 the utilisation of crystals and other detectors, such as the 



