388 
MR. C. A. BELL ON THE SYMPATHETIC VIBRATIONS OF JETS. 
speedily verified by attaching a light glass jet to a piece of soft iron, soldered, to a brass 
spring, and letting the soft iron take the place of the telephone diaphragm. (Fig- 1.) 
The results with this arrangement were still more satisfactory than those previously 
obtained, and speech as well as musical and other sounds were reproduced of con¬ 
siderable loudness, if not always very distinctly. A singular fact also revealed itself, 
viz., that the effects were about the same whether the vibratory motions of the jet- 
tube took place in the direction of its length or transversely. It should be mentioned 
that certain desirable conditions of air pressure, size of jet orifice, and size and 
distance of flame had previously been ascertained by experiment. 
At various times in the course of these experiments I had noticed that a flame 
against which an air-jet was playing under suitable conditions, was not only visibly 
affected by sounds, but that sometimes it seemed to speak back words uttered in its 
Fig. 1. 
neighbourhood, the repeated sounds being comparable to a feeble echo from a near 
surface. It was also found that a vibrating body, such as a tuning fork, held near the 
jet orifice, caused the flame to emit the sound corresponding to its vibrations. 
A jet of air, then, playing against a flame under proper conditions, formed a com¬ 
bination capable of reproducing, as sound, vibrations communicated to the air at the 
orifice, either from the air behind or external to the orifice, or from the jet tube or 
support. 
But, very strangely, scarcely any but irregular blowing noises could be heard from 
a vibrating jet when the ear, or the end of a tube communicating with the ear and 
large enough to receive the whole mass of air in the jet, was held opposite to it, 
instead of the flame. Tubes of various sizes, with conical and cylindrical ends, and 
held at various distances, were tried without result, until finally it became evident 
that the changes in the jet, effective in producing sound, must be relative changes of 
different portions of it. This view was also suggested by the appearance of the flame 
in the preceding experiments. At the plane of contact of the jet with the flame, a 
peculiar ring of blue flame could be seen, and this ring evidently vibrated violently 
while the flame was emitting sound (fig. 1). 
Accordingly, with the object of exploring every part of the jet, I took a hearing- 
