374 



Mr. C. A. BeU. 



[May 13, 



in the " nappe " or thin sheet of fluid formed when the jet strikes 

 normally on a small surface. So far then as vibratory changes are 

 concerned, the nappe has all the properties of the main stream. 

 Although the diameter of this excessively thin film is about the same 

 whatever be the distance of the surface from the orifice, the intensity 

 of the vibratory changes propagated to it varies with this distance, 

 as for the jet itself. It is simply necessary bhen to insert into the 

 nappe two platinum electrodes in circuit with a telephone and a 

 battery having an electromotive force of from 12 to 30 volts, to get an 

 accurate and faithful reproduction of the jet vibrations. Loud sounds 

 can thus be obtained from a jet which is finer than the finest needle, 

 and the arrangement constitutes a highly sensitive " transmitter." 



A jet transmitter, in its simplest form, consists essentially of a glass 

 jet- tube which is rigidly attached to a sound-board, and supplied from 

 an elevated reservoir containing some conducting liquid (distilled 

 water acidified with -g^oth of its volume of pure sulphuric acid is the 

 best) ; and a couple of platinum electrodes, embedded in an insulator, 

 such as ebonite, against which the jet strikes. The jet may issue from 

 a circular orifice, about ^-th of a millimetre in diameter, in the blunt 

 and thin-sided end of a small glass tube. Much smaller jets may be 

 used : but for one of the given size the pressure required for distinct 

 transmission of all kinds of sounds will not exceed 30 inches. The 

 receiving surface is the rounded end of an ebonite rod, through the 

 centre of which passes a platinum wire. The upper end of the rod 

 should be about 1 millimetre in diameter, and should be surrounded 

 by a little tube of platinum ; and the end of the central wire and the 

 upper margin of the tube should form a continuous slightly convex 

 surface with the ebonite, free from irregularities. The inner and 

 outer platinum electrodes are joined respectively to the terminals of 

 the circuit. The jet is allowed to strike on the end of the central wire, 

 and thence radiating in the form of a nappe, comes into contact with 

 the tube, thus completing the circuit. The dimensions of the 

 apparatus may be varied to suit jets of different sizes ; it is highly 

 desirable, however, that the jet nappe should well overlap the inner 

 margin of the ring-shaped electrode. 



With small jets the impact disturbances are so feeble that slight 

 precautions are necessary to insulate, the receiving surface from the 

 orifice, unless the former is placed low down in the path. The 

 strength of battery may be increased until the escape of electrolytic 

 gas-bubbles causes a faint hissing noise in the telephone. The liquid 

 on its way to the jet should pass downwards through a wide tube 

 lightly packed with coarse clean cotton, by which minute air-bubbles 

 which violently disturb the jet, and small particles of dust which 

 might obstruct the orifice, are stopped. This tube should never be 

 allowed to empty itself. 



