416 
MR. C. A. BELL ON THE SYMPATHETIC VIBRATIONS OP JETS. 
Savart and Magnus,* and easily verified by means of the “Jet Transmitter,’ that a 
jet from a perfectly circular orifice, carefully protected from vibrations, does not spon¬ 
taneously divide in a regular manner. On the contrary, rhythmical division only 
takes place under the influence of external vibrations, or of the disturbances produced 
by impact, or when the orifice is irregular. It was quite natural that this should have 
been denied by Plateau ; for it can be readily understood from the experiments given 
above, that perfect insulation of a large jet from the vibrations of any solid body on 
which it strikes, by means of which solid body the musical character of its vibrations 
could alone be ascertained, is extremely difficult. With small jets, however, such as 
can be used in the transmitter, this insulation is comparatively easy. Now, experi¬ 
ment shows that the electrodes may be placed even in the discontinuous part of a 
small well-insulated jet, and yet no musical vibrations be excited in the telephone. 
When we consider that the electrical method is so delicate, that the effects of com¬ 
municated vibrations are by it perceptible even at the orifice, it is difficult to believe 
that spontaneous rhythmical divisions could exist without manifesting themselves 
lower down. 
In the second place, the “ forces of figure ” which cause the resolution of a liquid 
cylinder at rest, cannot be considered as solely operative in bringing about the changes 
which take place in a jet vibrating under the influence of sounds lower in pitch than 
its normal. Experience shows that whatever may be the rate of the impressed vibra¬ 
tions, within the prescribed limits, and however complex their character, all produce 
disturbances which grow equalty along the jet. As I understand Plateau’s theory, 
developed bj T Lord Rayleigh, this would not be the case with disturbances growing- 
under the influence of surface tension alone. The forces of figure, then, either must 
act in some definite way in both cases; or, if in the latter, they are entirely subordinate 
to, and controlled by, the impressed forces, some further condition than the mere form 
of the jet must be taken into account to explain the difference. In fact, their sole 
action seems to be that they fix an upper and ill-defined limit to the rate of vibration 
of the jet. With all vibrations below this limit they do not in any way interfere. 
The conclusion to be drawn is rather that a jet, at least in its upper part, is not 
comparable to a liquid cylinder at rest. I shall show reason for believing that it 
may become so at a distance from the orifice; aud also that the resemblance may be 
more pronounced in large jets than in small ones. 
It is at once obvious that Plateau’s theory is cpiite inapplicable to gaseous 
jets,t the phenomena of which are strictly parallel to those of liquid jets, and 
identical with those of a liquid jet playing within a mass of similar liquid, in which the 
“ forces of figure ” are necessarily entirely abolished. An examination of some instan¬ 
taneous shadow-photographs of vibrating jets of air, rendered slightly opaque by smoke, 
has proved to me that these jets also present swellings and contractions precisely 
* Poggen. Anna!., vol. 95 (1885), p. 1, and vol. 106 (1859), p. 1. 
f See note on Lord Rayleigh’s mathematical papers. 
