MR. 0. A. BELL ON THE SYMPATHETIC VIBRATIONS OF JETS. 
401 
low whistled tones, and finally at a pressure of about 15 decimeters it will be affected 
by all the tones occurring in the human voice, and usually employed in music, with 
the exception of hissing sounds. At a somewhat higher pressure it will also be visibly 
affected by hissing noises. 
These effects are not confined to jets of the size mentioned, but are exhibited by 
much larger and much smaller ones. But the pressure required to produce any given 
range of sensitiveness increases with the size of the jet, approximately in accordance 
with Savart’s law. It is not easy, however, except by very careful construction of 
the orifice, to get jets of more than 1 to 1^ mm. in diameter to respond to sounds of 
very high pitch, without, at the same time, a great deal of accidental disturbance. A 
large jet also requires very careful insulation. On the other hand, jets of as small 
diameter as T2 mm. are well adapted to show the influence of pressure on sensitive¬ 
ness. But for such jets the pressure necessary to produce sensitiveness to any given 
tone does not even approximately follow Savart’s law, being higher than indicated 
by theory. Small orifices are also useless when sounds are to be produced by 
impact of the jet, and are very liable to become plugged by little particles of dust, 
unless the liquid supplied is carefully filtered. 
Now, let the hearing-tube, illustrated in fig. 5, be held in the path of the jet, so 
that the steam impinges on the centre of the membrane, and let the jet be subjected 
to any continuous vibration by which it is affected, while the ear-piece of the hearing- 
tube is held to the ear. The following may be noted :—When the membrane is held 
close under the jet orifice, no sound will be audible in the ear-piece; but as the 
receiving-tube is gradually withdrawn along the jet path, a sound will be heard 
corresponding in pitch and quality to the disturbing sound—provided, of course, that 
the jet is at such pressure as to be capable of responding to all the higher tones to 
which the disturbing sound may owe its timbre. The intensity of this sound grows 
as the distance between jet orifice and membrane is increased. Finally, while the jet 
is still continuous above the membrane, a point of maximum intensity and purity of 
tone will be reached ; and if the membrane be carried beyond this point the sound 
heard will at first increase in loudness, becoming harsh in character at the same time, 
and at a still lower point will degenerate into an unmusical roar. In the latter case 
the jet will be seen to break above the membrane. 
Although the jet in this experiment will respond to and reproduce all tones lower 
than the highest by which it is visibly affected, it will not reproduce all with equal 
intensity, but will be most powerfully affected by some one tone or set of tones, as 
pointed out by Savart. The highest of the proper tones of the jets is usually a 
fourth or a fifth lower than the highest which it is capable of reproducing. It is 
worthy of notice that jets from orifices not perfectly circular show this preference for 
certain tones more than strictly cylindrical jets; and it may possibly be that this 
preference is invariably the result of some irregularity in the orifice. The incon¬ 
venience arising from it when speech or music is to be reproduced, is practically 
MDCCCLXXXVI. 3 F 
