roe2 
NAPORE 
[APRIL 2, Tora 
wholly connected with the creation and modula- 
tion of the electric waves emitted by the sending 
station, and chiefly due to the difficulty of design- 
ing a microphone which can carry a sufficiently 
large current without heating. An additional 
trouble is that of devising a generator which shall 
be as simple and easily managed as that of a 
wireless telegraph plant. 
As regards the microphone, most workers have 
employed a number of carbon microphones joined 
in parallel so as to enable a high-frequency an- 
tenna current of, say, 4 or 5 amperes to be passed 
through them without overheating any one. It 
is not easy, however, to divide the current equally 
between the microphones, or to keep them abso- 
lutely in step with each other. Another type is the 
liquid microphone of Majorana, and of Vanni. In 
Dr. Vanni’s microphone a jet of water rendered 
slightly conducting by acid or salts is allowed to 
fall on a fixed inclined metal plate, B, and then 
Fic. 
1.—The liquid microphone of Dr. J. Vanni. 
bounces off on to another inclined metal plate, A, 
which is in mechanical or electrical connection 
with the diaphragm of a speaking mouthpiece (see 
Figs. 1 and 2). Speech, therefore, made to it 
sets the last-named plate vibrating, and thus 
breaks up and varies the resistance of the film or 
column of liquid connecting the two plates. 
Hence, if this liquid column is in the circuit of 
the transmitting antenna, any speech made to the 
diaphragm will vary the electrical resistance in 
the antenna circuit, and change in a_ similar 
manner the amplitude of the. radiated electric 
waves. 
W. Dubilier has also invented a water-cooled 
carbon granule microphone, the main diaphragm 
being moved by the current through a relay 
microphone to which the speech is actually made. 
This microphone can pass 700 watts with clear 
articulation (see Fig. 3). Then with regard to 
generators, a good many modifications of the arc 
generator have been produced. The Moretti are 
NO. 2318, VOL. 93] 
consists of a copper tube kept supplied with water, 
and another copper rod is brought down so as to 
strike the arc against the water. When the arc 
is formed with a continuous current, and is also 
shunted as above described with a condenser 
inductive circuit, high-frequency oscillations are 
set up in the latter. There is a very rapid extinc- 
tion and re-ignition of the arc, possibly due to 
some action like that in the Wehnelt interrupter. 
The writer of this article has also devised recently 
a new form of are generator which requires no 
transverse magnetic field, nor supply of hydrogen 
or coal gas, as in the Poulsen apparatus. We 
have, then, in addition, the high-frequency alter- 
nator method of creating the oscillations. Fessen- 
den experimented at one time very largely with 
such machines, devising a form of Mordey alter- 
nator which could give a frequency of 80,000 or 
100,000. The invention by R. Goldschmidt of a 
means of multiplying frequency by means of a 
Fic. 2.—Arrangements for circulating the liquid by a rotary pump R 
in Vanni's microphone. 
rotating field alternator made a new departure. 
By this machine high-frequency continuous oscil- 
lations are mechanically created, and their ampli- 
tude can be controlled by a microphone placed in 
the exciting circuit of the machine, so that it is 
not traversed by the main current. 
Furthermore, we have the high speed, smooth 
disc generator of Mr. Marconi as a means of 
creating undamped oscillations, and, in addition, 
a telephonic transmitter has been invented by him 
which has not yet been described in detail, but 
was mentioned by him in a recent lecture in Rome. 
It is known that he has recently directed his 
attention closely to invention in connection with 
wireless telephony. 
It is also possible to employ spark discharges 
of a very high spark-frequency, above the limit of 
audition, as a means of creating what are prac- 
tically unintermittent: oscillations, the separate 
trains of oscillations being practically in contact 
with each other. This method depends upon the 
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