MR. C. A. BELL ON THE SYMPATHETIC VIBRATIONS OF JETS. 
887 
in their neighbourhood. Bat very frequently the “ nappe ” emitted a harmonic of the 
exciting tone, instead of the tone itself. 
In 1884 Lord Rayleigh* demonstrated the sensitiveness to sound of jets of 
coloured water in water, and also published some interesting drawings of the appear¬ 
ances of these and of vibrating sensitive flames when viewed intermittently. 
The literature of sensitive flames is extensive, but it is not necessary to catalogue 
it here. 
My attention was directed to this subject in the following way :—Happening to 
hold the flame of a Bunsen burner in front of a small orifice in the end of a glass 
tube, from which a rapidly pulsatory jet of air issued, in such a way that the air- 
stream impinged on the flame, I noticed that a loud musical sound was produced, the 
pitch of which corresponded with the rapidity of the jet pulsations. So far there 
was little requiring explanation. But a feature of the phenomenon which strongly 
riveted my attention was this : that while the sound was of feeble intensity when the 
flame was quite close to the orifice, it increased in loudness as the lamp was withdrawn 
along the jet path, and reached its maximum with orifice and flame at a certain 
distance apart. Beyond this distance the sound rapidly degenerated into an un¬ 
musical roar. 
In order to study this phenomenon more carefully, a small round hole was pierced 
in the diaphragm of an ordinary hand telephone, and the chamber behind the 
diaphragm placed in communication with a reservoir of air under gentle pressure, 
which previous experiment had shown to give the best result. The telephone being- 
put into circuit with a battery and rheotome in a distant room, each motion of the 
diaphragm inwards naturally produced compression of the air in the chamber behind. 
A small flame being placed in front of the orifice, it was found that not only 
musical vibrations, but also the more complex vibrations of speech, impressed upon 
the diaphragm, could be quite loudly reproduced. In fact, when the telephone was 
put in circuit with another telephone, or better with a battery and microphone in the 
distant room, speech loud enough to be heard over a small apartment could be readily 
produced. The words, however, were certainly lacking in distinctness. 
A most natural assumption was, that the sounds heard resulted from the impact of 
a series of puffs of air against the flame. Accordingly I attempted to produce a 
greater volume of sound by increasing the number of jets. Several small round holes 
were pierced in the telephone diaphragm, and a separate flame placed in front of each 
of them. The experiment did not justify my anticipations; for it soon appeared that 
by far the most effective jets were those that issued near the centre of the diaphragm, 
where the greatest motion existed ; an orifice near the circumference of the diaphragm 
yielding only feeble sounds. In fact it looked as if motion of the orifice, rather than 
compression of the air, was the chief agent in the phenomenon. This conclusion was 
* Phil. Mag., ser. 5, vol. 17 (1884), p. 188. 
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