406 
MR C. A. BELL ON THE SYMPATHETIC VIBRATIONS OF JETS. 
acid, esj^ecially free from lead. This amount of sulphuric acid cannot be much 
exceeded without impairing the sensitiveness of the jet, probably by increasing the 
viscosity of the liquid. 
By means of a battery, a telephone, and a couple of platinum electrodes, we can 
examine every part of a jet of this acidulated water ; and the method is so delicate 
that changes can be detected in every point from the orifice to the discontinuous 
portion. 
That vibratory changes are initiated in the jet stream at its origin, and during its 
passage through the orifice, may be proved by connecting the inner and outer 
electrodes of a jet tube similar to that shown in fig. 6 with the terminals of a circuit 
including a telephone and a battery of a few elements. Vibrations impressed on the 
jet orifice will then be transmitted to the telephone ; and if the jet tube be mounted 
in a proper sound-board the most complex sounds may be reproduced. But the 
reproduction, although admirably distinct, is always feeble, as might naturally be 
expected. The pressure necessary for distinct articulation is not so high as that 
required when the electrodes are placed at a distance from the orifice. From this we 
may infer that very rapid vibrations may exist in the liquid at the orifice, which are 
only propagated along the jet when the stream attains a certain velocity. 
Very similar results are obtained if the jet nozzle be made of platinum, and the 
jet be allowed to strike upon the rounded end of a platinum rod placed at a little 
distance from the orifice. The current may be passed in either direction between 
nozzle and rod. The best sounds are obtained in the telephone when the end of the 
rod is a little beyond the “ vena contracta.” 
It is evidently impossible to include any length of the jet at a distance from the 
orifice in a circuit, without transforming it into a nappe ; and I have therefore taken 
advantage of the fact that so far as vibrations are concerned the nappe has all the 
properties of the jet stream itself. The nappe formed by the impact of a steady 
jet against an extended flat surface is of about the same diameter, whatever may 
be the distance of the surface from the orifice, so long as it is formed from the 
continuous portion ; but the intensity of the disturbances transmitted to it from 
the orifice increases with the distance, as for the jet itself. The simplest way of 
passing a current through it consists in allowing the jet to strike normally upon 
the exposed end of a platinum wire imbedded in an insulator, such as ebonite, which 
is impervious to, and unaffected by, the liquid employed. The jet spreads out from 
the point of impact as a nappe, which comes in contact with a platinum ring- 
imbedded in the same surface. The wire and ring are made to serve as electrodes. 
A very simple form of apparatus is shown in section in fig. 8. The jet tube, J, 
is mounted in the sound-board, S. The receiving- surface is formed by the end of 
an ebonite plug, P. A platinum wire, E, passes water-tight through this plug, its 
exposed upper end forming the inner electrode of the “Transmitter.” The outer 
electrode, E', consists of a little tube of platinum foil which surrounds the wire, E, 
