MR. C. A. BELL ON TEE SYMPATHETIC VIBRATIONS OF JETS. 
403 
the centre of a parchment drum, which may be carried to a considerable distance. 
The connecting cord being stretched, an assistant may be directed to speak or sing 
to the distant drum. Or for the air-jet attached to the armature of a telephone 
magnet, shown in fig. 1, we may substitute a water jet, directed against a suitably 
placed membrane. 
When spoken words are reproduced in these and similar ways, if the pressure in 
the reservoir be allowed to fall below that required for distinct speech, the 
characteristic quality of the speaker’s voice, which is largely due to overtones, will 
first be lost; at still lower pressure, certain sounds and syllables will be missed, and 
the words will become unintelligible. On the other hand, if the pressure be somewhat 
above the necessary limit, a peculiar nasal quality will be added to the voice, due 
probably to the greater reinforcement of vibrations of high pitch. At still higher 
pressure the reproduction will become feeble, and crackling noises, due to minute 
air-bubbles in the liquid and other accidental causes, will become painfully loud in 
the ear-piece. 
Fig. 6. 
When the jet liquid is a non-conductor vibration may also be excited in it by 
electrical disturbances at the orifice. The jet-tube (fig. 6) is best made of glass. The 
orifice having been formed, the tube is thoroughly cleansed, and coated outside near 
the orifice with bichloride of platinum solution mixed with mucilage, dried, and heated 
to redness in the flame of a lamp, until metallic platinum is burnt into its surface, 
which can be effected without destroying the shape of the orifice. A fine platinum 
wire wound round the platinized portion of the tube forms one terminal of a secondary 
telephonic circuit, and a slip of platinum foil within the tube forms the other. The 
