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MR. C. A. BELL ON THE SYMPATHETIC VIBRATIONS OF JETS. 
On now introducing the small hearing orifice into the path of the jet, it was found 
that just beyond the breaking point an indistinct or harsh repetition of the disturbing 
sound was heard ; that just at, or a little inside of, this point the repeated sound was 
clear and of maximum intensity; and that it died away as the hearing orifice was 
moved from this position, either towards the jet orifice or out of the line of the jet 
axis (fig. 2). Substituting a small flame for the hearing-tube, the greatest loudness 
and purity of tone were obtained when the flame was placed just within the breaking 
point; and on moving the flame the same changes in loudness and distinctness were 
noted as occurred with the hearing-tube. 
In this experiment it was found most convenient to cement the jet-tube to the 
armature of an electromagnet, thrown into vibration by a battery and rheotome. 
The attention of the experimenter could then be fixed solely on the sounds proceeding 
from the jet. 
This experiment was repeated many times, the jet being subjected to vibrations of 
varying pitch and intensity. The result was always the same. Whenever the jet 
“ broke ” in front of hearing orifice or flame, under the influence of a pure musical 
tone, either it gave forth no sound, or the sound heard was harsh and rattling in 
character. In the latter case the rhythm of the impressed vibrations was preserved, 
but the quality was lost. 
In repeating these and similar experiments certain precautions should be observed, 
some of which have been pointed out by other experimenters in this direction. 
The edges of the jet orifice, and of the receiving orifice, ought to be perfectly smooth 
and circular. Any irregularity in them tends to cause whistling or scraping noises in 
the hearing-tube, and also makes the jet more liable to “ sing,” in a manner presently 
to be described. 
The air passage, from the reservoir to the orifice, should be wide and unobstructed. 
It is therefore better to control the outflow by regulating the pressure in the 
reservoir, rather than by any form of valve. 
The air should be free from dust, and from suspended particles of water. Each 
little particle, as it passes the orifice, gives rise to a disturbance which grows as it 
travels along with the jet, and causes a crackling noise when it reaches the hearing 
orifice. Should the air be very dusty there will be a distinct gam by filtering it 
through a wide tube lightly packed with coarse cotton. 
The apparatus actually necessary for these experiments is extremely simple. The 
air reservoir may take the shape of a bag made from a single sheet of thin vulcanized 
rubber cloth, five feet long by two feet broad, folded once and joined along its edges 
with rubber cement. Ordinary gas bags are much too stiff and heavy for the low 
pressures required, and elastic bags are quite useless. Into one corner is cemented 
one limb of a three-way stop-cock; of the remaining limbs one is connected to a 
laboratory blower, and the other leads to the jet by a wide rubber tube 
Pressure is best applied to the bag, after it has been inflated by the blower, by means 
