410 
ME, C. A. BELL ON THE SYMPATHETIC VIBRATIONS OF JETS. 
action. In the ordinary jet transmitter, this polarization of the electrodes, when 
they are small, is exceedingly intense. If, while the jet is playing, the current be 
sent between them for a few seconds, and the battery be then suddenly cut out of the 
circuit, the jet will continue to transmit vibrations to the telephone with gradually 
increasing feebleness for a minute or even longer. No such effect can be obtained of 
course with the transmitter having zinc electrodes and a jet of zinc sulphate solution. 
Owing to this intense polarization it is quite impossible to measure the resistance of 
the nappe by any of the usual methods, which might be interesting as enabling us to 
estimate the thickness of the film. A small transmitter inserted in a Wheatstone 
Bridge will show an apparent resistance, varying with its dimensions and the strength 
of current, from 1,000 to 1,500,000 ohms. This resistance is also extremely variable, 
even for the same battery and transmitter: it seems to be influenced by the direction 
of the current between the electrodes only when these are of unequal size. 
Now it is well known that part at least of the resistance included under the term 
“ polarization,” is dependent on the state of rest or motion of the liquid at the surfaces 
of the electrodes ; and if changes occur in the motion, rectilinear or rotatory, of the 
jet particles, such changes might certainly influence this mechanical polarization, and 
thereby affect the strength of the current. I have already given one experiment 
which shows that vibrations induce changes in the relative velocity of the particles 
along the axis of the jet. The following experiment furnishes an additional proof. 
Just as the impact of a vibrating air-jet, playing in air against an orifice, may excite 
sound, so the impact of a water jet playing against electrodes immersed in water, may 
excite electrical undulations. In fact if both jet tube and electrodes of a polarizing 
transmitter be immersed in a vessel containing the same fluid with which the jet is 
supplied, the transmitter will not cease to operate, provided that the electrodes are 
brought much closer to the orifice : for the continuous portion of the jet now becomes 
much shortened, owing to friction against the surrounding fluid. The diagram 
(fig. 10) represents the most striking form of the experiment. 
The jet plays against the exposed end of a fine platinum wire, P, firmly embedded 
in the centre of a small ebonite rod, R, which passes through the bottom of the trough 
T. A side tube, L, carries off the overflow from the trough. The end of the 
wire P, and a small platinum plate Q immersed in the liquid of the trough, form 
the electrodes between which the current is passed (in either direction). The 
telephonic effects with this arrangement are exactly similar in kind to those 
obtained from an air-jet with a small hearing orifice. The loudest sounds are 
heard when P is placed in the axis of the jet at a certain distance from the orifice ; 
and the reproduction grows fainter as the electrode P is moved from this position, 
either towards the orifice or laterally. 
The telephonic effects are feeble, but such as they are they cannot be attributed to 
the interposition of varying liquid resistances between the conductors. 
Under these conditions, in fact, a liquid jet becomes comparable to a jet of air. 
