Daily Kennebec journal. [microfilm reel] (Augusta, Me.) 1870-1975, 1911-02-03
Lessons IN Science
WIRELESS TELEPHONY.
The DuddelI Arc.

The Duddell or singing arc, as
modified by Poulsen, affords very
easy method of securing continuous
"a diation of electric waves of sub
stantially constant amplitude. The
microphone circuit can be associated
with the inductanCe coil of the prim-
ary oscillating circuit, or inductively
ASSOCIATED with one of the leads sup
plying direct current to the arc. Or
the microphone may be associated
with one of the field windings of the
supply generator. BY these means
fluctuations of the electric currents,
or of the current passing across the
are are obtained. in accordance with
resistance changes produced in the
microphone by the voice.
The Tclefunken company has used a
number of modified Poulsen acres in
series as the generator for the high
frequency oscillations. and Fessenden
has also employed high-voltage arcs
burning in compressed gas for the
|same purpose. John Stone. following
the discovery of Elihu Thomson, used
Ian arc with water cooled electrodes in
lair and direct voltage of several
thousand volts. This avoids to some
extent the wasting away of the car
bon electrodes and the irrcguarities
and frequent adjustments OF the are.
In the early De Forest sets, in which
the carbon copper are was used as a
generator, the microphone was placed
directly in the ground circuit OF the
|antenna and as near the earth as
possible. To avoid destruction OF the
microphone from high voltages it is
generally necessary TO place the
microphone in the earth side Of this
circuit. This is an arrangement now
frequently employed both in Europe
and America. In the newest De For
est sets a specially constructed "Os-
cillator" is used in place OF the arc.
This employs cooled electrodes. and
burns in an artificial atmosphere. but
without the necessity for high volt
ages. The system is sufficiently sim
pie to be operated by one not an eN-
pert, and is capable of voice trans
mission from ordinary antenna of 30
to $50 miles.
The ordinary microphones are
destroyed if one ampere or more is
passed through them for any length Of
time. For fifty miles and greater
ranges, currents Of one and one half
to three amperes are required in the
antenna Of the transmitting station.
This calls for specially designed mi
crophones with large amounts OF car
hon granules and large electrodes; or
else for cooled microphones.
De Forest employs microphone in
which each electrode. and the carbon
containing chamber as we'll. are wa
ter jacketed. The same water cir
culating system used 10 cool the
electrodes of his oscillator serves also
TO cool the microphones.
For very large currents. such as are
needed for much greater ranges OF
wireless telephony than are yet sue
cessfullr covered. a new principle will
probably replace the carbon micro
phone. De Forest has suggested a
monometric gas fame. rendered cleo
trically conducting. and controlled by
the speakers voice.
y current governing, yoice-con
trolled medium of this nature will be
capable of governing very large
amounts of energy in an instantaneous
manner. and seems to offer the key to
the problem of long distance wireless
telephony.