408 
MR. C. A. BELL ON THE SYMPATHETIC VIBRATIONS OF JETS. 
connected with the reservoir. Two perforated discs of ebonite are fitted within 
the cylinder, and the space between them lightly packed with coarse cotton, which 
has been previously treated with caustic potash, and thoroughly washed with dilute 
sulphuric acid and water. This filter serves to hold back bubbles of air and little 
particles of dirt which might stop up the orifice. 
The strength of battery to be used with this “Jet Transmitter ” will depend 
chiefly on the nature of the jet fluid. With the solution of sulphuric acid above 
recommended, and platinum electrodes, the resistance of the film, and the polarization 
resistance at the contact of the liquid and electrodes are so great that a battery of 
high electromotive force is required. But for the same reason the resistance of 
battery and line is of little consequence, and a large number of elements of small 
surface may be used. About twenty little zinc-carbon cells charged with a solution 
of sal ammoniac answer well, but this number may be exceeded with advantage. 
Such a battery does not sensibly polarize when connected through the film. The 
strength of battery cannot however be indefinitely increased; for a point is soon 
reached at which noises in the telephone, due to the escape of electrolytic gas-bubbles 
from the electrodes, completely drown the sounds due to vibratory changes of the jet. 
But long before this occurs, sounds of all kinds are loudly reproduced. 
As I have before stated, this instrument may be adapted to jets of various sizes, 
the dimensions and distance apart of the electrodes being regulated by the diameter 
of the nappe. I have had them constructed with jets only yth of a millimeter in 
diameter, discharging about 6 c.c. of liquid per minute under a pressure of about 
45 centims. Even such small jets are capable of transmitting speech loudly and 
distinctly ; but it is difficult to get from them a good nappe, the liquid having a great 
tendency to accumulate on the electrodes instead of flowing evenly away. When the 
nappe is very small, the electrodes may therefore advantageously be formed by the 
exposed ends of two fine platinum wires. 
With these small instruments it is easy to demonstrate all the principal properties 
of jets; the absence of spontaneous vibrations, the dependence of the pitch of the 
fundamental tone and of range of sensitiveness on the diameter of the orifice and 
the pressure, the growth of disturbances along the jet path, &c. 
There are two ways in which the jet may be supposed to act on the electric current. 
It is a fact of observation that the diameter of a vibrating jet at any point is constantly 
varying ; and we may suppose the successive protuberances and constrictions which 
it exhibits, and which appear in the nappe as waves radiating from the point of 
impact, to interpose a continually changing resistance in the circuit; or again, the 
interruptions to the electric flow may take place at the contact of the liquid with 
the electrodes, being due to changes in the character of the motion, rectilinear or 
rotatory, of the liquid particles. Probably, as I hope to show, the effect is a 
compound one, due to both causes. 
That the first of these hypotheses is amply sufficient to account for the observed 
