414 
MR. C. A. BELL ON THE SYMPATHETIC VIBRATIONS OF JETS. 
neighbourhood losing their effect gradually ; and it is by no means certain that, other 
conditions being equal, it is the same for different gases, or for different liquids. 
At a distance from the oritice, depending on the intensity of the original disturb¬ 
ance, the constricted portion of the jet gives way, a break in the stream being the 
result. A succession of vibrations impressed upon the orifice therefore cause the 
stream to resolve itself into drops. 
When the impressed vibrations are complex the length of the column corresponding 
to each presents minor constrictions and expansions, sometimes of very complicated 
outline. Breaks in the stream occur first at intervals corresponding to these lengths : 
the detached portions tending further to resolve themselves at a greater distance from 
the orifice. 
The formation and growth of the swellings and contractions are attended by 
corresponding changes in the velocities of the axial particles of the jet. These 
changes may be characterised as accelerations and retardations of the velocity measured 
along the jet path. 
When a jet escapes into a fluid which offers a sensible resistance to its motion, its 
axial particles suffer a gradual retardation. But this retardation is greater when the 
jet is disturbed by vibrations than when it is in its normal condition. 
Such are the phenomena; how far are they explained by theories hitherto accepted ? 
In view of the striking parallelism of the properties of gaseous and of liquid jets, it 
will hardly be considered inadmissible to assume that the most satisfactory explana¬ 
tion will be that which refers both to the same origin. In the two kinds of jets we 
have the same tendency to vibrate at some definite rate ; the same growth of vibra¬ 
tory changes along the jet path ; similar phenomena of discontinuity manifested at 
a certain distance from the orifice ; and similar changes in the motion of the particles of 
fluid along the axis. 
Say art and Sondhauss have occupied themselves chiefly with the origin of 
normal vibrations : Plateau alone explained not only their origin but also their 
growth. Now, simple inspection of the table given by Savart of tones generated in 
a tube reservoir by efflux of water from an orifice in its lower end, shows that these 
tones are much higher in pitch than those which would result from the impact of the 
jet against a stretched membrane. Vibrations originating in this way cannot therefore 
account for the normal jet vibrations, which are invariably connected with impact. 
With regard to Sondhauss’s idea, viz., that the jet is comparable to a solid rod 
thrown into vibration by friction against the orifice, it must be admitted that the 
analogy was not wholly without foundation. If spontaneous vibrations be excited in 
an air-jet in the manner I have described, it will usually be found that the pitch of 
the tone rises as the hearing orifice is moved towards the jet orifice. But-this does not 
go on indefinitely ; for after the tone has risen through an interval of about a third, it 
suddenly returns to its original pitch, again rises, again falls, and so on, until the 
impact disturbances become too feeble to re-act upon the fluid at the.orifice. The 
