404 
MR. C. A. BELL ON THE SYMPATHETIC VIBRATIONS OF JETS. 
primary circuit may include a microphone or a rheotome, and a battery. The 
vibratory changes in the potential of the two secondary terminals of the circuit, 
caused by vibrations impressed on the microphone or rheotome, excite disturbances in 
the jet, which may be reproduced as sound. When, for example, words are spoken 
to the microphone, these words are accurately repeated in the ear-piece connected 
with the hearing membrane on which the jet plays. 
The action in this case may depend on changes in the surface tension of the 
liquid at the orifice, accompanying the electrical changes. Distilled water, alcohol, 
ether, petroleum, &c., may be used as the jet liquid. Small quantities of saline 
substances in solution, and especially any slight trace of mineral acid, effectively 
destroy the sensitiveness of water, by increasing its conductivity. 
This method may be variously modified. For example either the outer or the inner 
electrode may be dispensed with, and the corresponding secondary terminal joined 
to earth. 
A striking difference must have been noticed between the methods by which 
gaseous and liquid jets are made to excite vibrations in air. Whereas very little 
sound results from the impact of an air-jet on a membrane, very loud sounds are 
produced by the impact of a liquid jet. This might seem to indicate a difference in 
the character of the motions excited by vibration in jets of the two kinds of fluid. 
Nevertheless, it can be shown that changes occur in the normal velocity of the central 
portions of a vibrating liquid jet, and that these are sufficient to excite sound. Let 
the jet strike upon a stout brass plate, A (fig. 7), pierced with a small orifice, B, which 
leads to a small flat chamber, of which the brass plate forms one side. The opposite side 
of this chamber is formed of a thin metal diaphragm, D, through which the pulses 
generated in the chamber are communicated to the hearing-tube. Just as in the 
case of the air-jet, the loudesf sounds are heard when this orifice receives the central 
portion of the liquid jet. Feebler sounds are produced from the compact of 
surrounding portions of the stream, or the jet-nappe. The chamber between A 
and D should of course be entirely filled with liquid ; a second ajaerture, B', allows 
the contained air to escape. 
One of the most effective and most interesting methods of studying the vibrations 
of a liquid jet consists in including a portion either of the continuous column, or of the 
jet-nappe, in circuit with a battery and a telephone, by which means its vibrations 
become audible in the telephone. This method may be used with jets of all sizes, but 
most advantageously with very small ones; and as by its means something may be 
learnt of the changes occurring within the stream, I purpose to describe it at some 
length. By making use of small jets we get rid of the necessity for “ insulating ” the 
jet orifice ; for the disturbances produced by impact are then so feeble as to be 
practically without effect. The jet is received on a smooth hard surface, which is 
scarcely capable of communicating disturbance to the surrounding air. 
Before describing the method it is well to recall one of Savaiit’s observations. In 
