330 KENNELLY AND UPSON— HUMMING TELEPHONE. [July 20, 



F. Gill,'' read before a meeting of the Dublin Local Section of the 

 Institution of Electrical Engineers in April, 1901. Very briefly, the 

 salient experimental facts reported in this valuable paper are : 



1. The reversal of the telephone receiver connections in the cir- 

 cuit alters the pitch of the auto-excited tone, the pitch being higher 

 for one direction, and lower for the other direction, of connection. 



2. The pitch of the tone may also be altered by changing: (a) 

 the inductance, capacity or resistance of the circuit, or circuits; (&) 

 the strength of current in the microphone transmitter; (c) the dis- 

 tance between the receiver and transmitter diaphragms; (d) pres- 

 sure on either of the diaphragms. 



The Gill paper does not discuss the theory of the subject beyond 

 suggesting that the phase retardation of the acoustic impulses reach- 

 ing the transmitter from the receiver has a controlling influence on 

 the pitch of the tone. 



The research reported in this paper may be regarded as extend- 

 ing the investigation from the stage reached in Gill's paper to a 

 stage which admits of a first approximation theory. A large amount 

 of research remains, however, to be carried on in the future, before 

 the experimental and theoretical analysis of this fascinating but 

 complex phenomenon can be regarded as satisfactorily nearly 

 complete. 



Method of Observation Employed. — As pointed out in Gill's 

 paper, the pitch of the note emitted by the humming telephone, 

 although substantially constant under fixed conditions, is affected by 

 almost any change in the apparatus, in a seemingly most intricate 

 manner. In order, therefore, to study the effect of varying one 

 particular variable at a time, the device was hit upon of acoustically 

 connecting the receiver and transmitter diaphragms in a definitely 

 controllable way by means of telescoping tubes fitting on to the 

 receiver and transmitter faces. These tubes, and also the standard 

 electric connections employed, are indicated in Fig. i. 



The transmitter was kept stationary, with one end of the tube 

 covering and secured to its cone. The receiver was fastened, on 

 a sliding wooden carriage, to the other end of the telescoping tube. 



^" Note on a Humming Telephone," by F. Gill, Journal of the Institution 

 of Electrical Engineers, 1901-02, Vol. XXXI., No. 153, pp. 388-399. 



