MULTIPLEX TELEPHONY AND TELEGRAPHY — SQUIER. 



147 



tjje design adapted for wireless telephony, the coefficient of coupling 

 being adjustable between wide limits. It was therefore a matter of 

 hours to run through a large number of experiments in which various 

 combinations were tried. 



The transmitters first tried were those of the microphone type 

 inserted in the armature circuit of the dynamo and provided with 

 water cooling when currents of several amperes were to be used. 



It was soon found, however, that the efficiency of transmission of 

 this cable line was so good for electric waves of these frequencies that 

 a very small current, in the neighborhood of 2 milliamperes, sent into 

 the line was amply 

 sufficient for good 

 speech at the re- 

 ceiving end about 

 7 miles distant. 

 No attempt was 

 made to determine 

 to what lower limit the transmission current could reach in this 

 respect, but such small currents enabled the ordinary telephone 

 transmitter to be used without any provision for cooling, especially 

 when it was inserted in the line circuit instead of in the armature 

 circuit of the dynamo. 



The telephone receivers were those regularly furnished for wireless 

 telephony, ranging in resistance from 2,000 to 8,000 ohms. 



Resonance. — As was expected, the phenomena of resonance under 



Fig. 5. 



Fig. 0. 



the conditions which here obtained were very pronounced and highly 

 consistent, since there is here a definite circuit free from the disturb- 

 ances and variations inherent in radio telegraphy and telephony. 

 In wireless telegraphy and telephonj^ it is well known that within a 

 few minutes transmission will drop off many fold from causes not en- 

 tirely understood, and from diurnal variations and electrostatic dis- 

 turbances, effective transmission is often prevented. 



In general, the different circuits were tuned to resonance in the 

 same manner, for the same purpose, and with -the same effect as in 

 wireless telephony and telegraphy. 



