THEORY OF THE IIOWLIKG TELEPHONE 



35 



and G were obtained. It is thus seen that for a given type of trans- 

 mitter if the direct current and any one of the four quantities e, h, z, 

 or T are known, the others are determined and may be obtained from 

 suitable curxes. 



40 80 120 IfcO 200 240 280 320 _ 3feO 



VALUES OF T (OHMS) 



Fig. 6 



Commercial receivers and transmitters have constants which vary 

 largely from those given above. These values represent the general 

 behavior of such instruments and are useful in understanding their 

 operation in a howling circuit. Inasmuch as the performance of such 

 instruments particularly the transmitter depends very largely upon 

 the condition of operation the constants given cannot be applied 

 with confidence to conditions greatly different from those mentioned 

 in the paper. With these facts concerning telephone instruments 

 in mind we are now in a position to treat some special cases. 



Case 1 — Diaphragms Connected Mechanically by a Rigid 

 AND Weightless Lever 



To illustrate the method of solution this special case will be solved 

 in some detail. A diagrammatic sketch illustrating the connections 

 is shown in Fig. 7. Neglecting the reaction of the air, the vibration of 

 the receiver diaphragm is controlled by the force Zi exerted by the 



