MR. C. A. BELL ON" THE SYMPATHETIC VIBRATIONS OP JETS. 
309 
are as sensitive, if not more so. To produce powerful effects by sound on liquid 
jets, it is therefore necessary to supply a lever, by means of which aerial sound-waves 
may act on the orifice at greater mechanical advantage. Such a lever is afforded by 
rigidly attaching the jet-tube to a sound-board which offers a large surface to the air. 
In many cases, indeed, the support or table on which the jet apparatus rests will 
answer all purposes; but generally it is better to attach the jet tube to a pine-board, 
about a quarter of an inch thick, and having a surface of about one square foot. A 
board of this thickness is preferable to a thinner one, since it is not so apt to play the 
part of a resonator, while it is equally effective in collecting sound impulses from air. 
Provided its surfaces are free, it is of little consequence how it is supported ; but it 
may be conveniently attached to props at the four corners. It is also a matter of 
indifference whether the jet tube is parallel or perpendicular to, or forms any angle 
with, the sound-board. 
Fig. 5. 
The apparatus shown in fig. 5 is sufficient for all ordinary experiments. The 
sound-board, S, is screwed to two brackets, projecting from the stout vertical board, 
Y. The latter is supported on leaden or india-rubber feet in such a way that the 
sound-board projects over a sink or trough. 
The jet tube, J, fits in a slotted brass tube, T, which is soldered in the centre of 
a circular brass plate, Q, about two inches in diameter. This plate is pressed flat 
against the sound-board by two stout springs, P and P'. A hole in the sound-board, 
about three-quarters of an inch in diameter, allows the jet tube to project through 
it, and to be moved a little sideways. The jet tube can thus be easily changed. 
The receiving surface is formed by a thin rubber membrane, stretched over the 
end of a brass tube, It, about fths of an inch in internal diameter ; this tube is 
provided with a lateral branch, inclined slightly upwards, to which the hearing 
tube, H, is attached. The tube, R, slides smoothly up and down within the 
slightly larger tube, L, fixed on a heavy leaden base, C. This arrangement 
