426 Mr. O. Heaviside on Telegraphic 



of the resonator. We here suppose that the natural pitch of the 

 resonator, agreeing with that of the external source, is estimated 

 after allowance for this correction, and may then leave this term 

 out of account. Otherwise, of course, the condition of synchro- 

 nism is not properly satisfied. In order that the force tending 

 to increase the vibration without limit may vanish, we must 

 have 



so that 



X = —-iX^ . 



When the pitch is given, the total current through the mouth 

 of a resonator in synchronism with the source is independent of 

 the form of the resonator, provided that the mouth is furnished 

 with the flange. In the absence of a flange, the relation between 

 X and yfr would be sensibly altered. The effect of the resonator 



in external space depends only on X, and is therefore always 

 the same, but inside the reservoir will be inversely proportional 

 to the capacity S. Hence, in order to get a great internal effect, 

 the reservoir should be made small, and the pitch kept down to 

 the required point by elongating the neck. 



It is proper to state that the preceding theory is at variance 

 with that given by Helmholtz"*, who treats the potential -\/r as 

 vanishingly small in comparison with that due to the resonator 

 (f> . Helmholtz is thus led to the conclusion that a simple 

 source would be intensified by the neighbourhood of a resonator. 

 If it be thought strange that the very powerful motion within 

 the resonator should produce no more effect than the external 

 source, it must be remembered the small tendency to escape is 

 the very reason of the accumulation. 



LIV. On Telegraphic Signalling with Condensers. 

 By Oliver Heaviside, Esq.f 



GIVEN an insulated conductor called the line connecting two 

 places, there may be said to be in present use two distinct 

 methods by which signals made at one end of the line are ob- 

 served at the other. The first, which is that in most general use, 

 is to connect the line with one end of the coils of an instrument 

 affected by electric currents, and the other end of the coils with 

 earth. The battery at the sending-end being also placed between 

 the line and the earth, a circuit is established, through which a 

 current will flow so long as the battery and instrument remain 

 undisturbed. This current will in a short time after the first mo- 



* Tonempfindungen, Beilage ix. 

 t Communicated by the Author. 



