MULTIPLEX TELEPHONY AND TELEGRAPH Y—SQUIER. 147 
the 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 ofthese 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 
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Fia. 6. 
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 telephony 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. 
