228 



ANNAL,^ NEW YORK ACADEMY OF SVIEA'CEf^ 



a positive charge is placed on the grid, an increase iu the wing current 

 results, the alternating component of the wing current charging the con- 

 denser C\ and the sum of the currents passing through ('^ and L^ equal- 

 ing the current through the audion. When a negative charge is placed 

 on the grid the current through the audion is reduced and the inductance 

 L. discharged into the condenser shunted across it, charging it in the 

 opposite Avay to that caused by the increase in the wing current. In both 

 cases, C4 then discharges through the grid circuit, reenforcing the oscil- 

 lations therein. 



Audio Frequency Amplification 



It is possible to combine with any of these systems a system of audio 

 frequency circuits which amplify the telephone current in exactly the 



Fig. 22 



same manner as the radio frequency oscillations are amplified, and such 

 a system is shown in Pig. 22. Here M^ represents the coupling of the 

 radio frequencies, and the coils are of relatively small inductance. M^ 

 is the coupling for the audio frequencies, and the transformer is made up 

 of coils having an inductance of the order of a henry or more. The con- 

 densers Cg and C^ having the double purpose of tuning Mo to the audio 

 frequency, and of by-passing the radio frequencies. The total amplifica- 

 tion of weak signals by this combination is about 100 times, with the 

 ordinaiy audion bulb. On stronger signals, the amplification becomes 

 smaller as the limit of the audion's response is reached. 



