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BELL SYSTEM TECHNICAL JOURNAL 



5,000 cycles per second. Beyond 5,000 cycles per second, the energy 

 is so low as to be impossible of measurement with the apparatus used. 

 A Weston Type 322 microammeter recorded the couple current for the 

 tuned circuit side of the twin single stage amplifier. With this instru- 

 ment and the thermocouple used, 0.2 microampere in the couple circuit 

 corresponds to one-quarter of a milliampere in the heater, and this is 

 the lowest readable deflection of the Weston instrument. 



Reduction of Observations 



Three corrections have to be made, the first being the correction 

 for varying volume. 



Simultaneous observations are made, at each setting of the tuned 

 circuit, of the filtered and the unfiltered energy of each syllable. It 

 is not possible to utter a given syllable with the same intensity and 

 at the same distance from the transmitter for every one of twenty- 



FT?EQliEnCY 



Fig. 3 — Illustrating Correction of ObservaLions, Necessary Because of Variation in 

 Resolving Power with Frequency Setting 



three times. Accordingly, the "unfiltered" readings are averaged and 

 each of the filtered readings for each syllable reduced from the value 

 actually observed to the value that would have been read had the 

 volume and distance been such as to give the average "unfiltered" 

 reading. This procedure is quite legitimate if it be granted possible 

 to maintain a definite composition of the syllable in question through- 

 out the changes of the tuned circuit setting. 



