Evening star. [volume] (Washington, D.C.) 1854-1972, 1910-02-13

WE are accustomed to the sound of the
w human voice as reproduced by the tele-
phone or monograph but to hear 1t coming
from the midst of the intense heat of an electric
would indeed be a novelty. But, strange
as it may seem, the ordinary arc light can be
made, by means of simple arrangement, not
only to talk. but to laugh, sing, reproduce music
of any Sort in short do all that may right
fully be expected from well trained phono-
graph.
At first sight this discovery seems to present
some startling possibilities. The street corners
might advantageously be made distributing
centers of news and information of general in
terest. Thus, in the early evening, later, on
summer nights open air concerts could be
given for the benefit of the city at large. Still
later perhaps in the small hours of the morning,
stirring temperance lectures, coming as 1T were
out of the Clouds might be followed by wave
of moral reform.
The line of thought is seductive one. Other
and greater possibilities suggest themselves
galore; but unfortunately for all of them the
speaking arc has the discouraging handicap of
a very weak voice. After careful training and
IN the most advantageous circumstances 1t may
be rendered loud enough to be heard by room
full of people; but the difficulties are such that
1t IS doubtful if our street lamps will ever be-
come the means of dispensing intellectual-as
well as electrc-l1ght
AS curiosity however, it is striking and its
explanation fairly simple In order to under
stand it, let us consider what the general con-
ditIons are, far as know them in the
ordinary electric The most salient fact IS
that here in region of only small fraction of
a cubic inch in volume energy is being liberated
at rate equivalent to a horsepower or more.
This results IN the highest temperature we have
yet been able to produce, or in the neighbor-
hood of sixtyhve hundred degrees Fahrenheit;
consequently the is a region of intensely
heated gases and vapors.
Now it is readily understood that an increase
in the current carried by the arc would in gen
eral mean an increase of its temperature, and
hence small expansion of the gaseous envelop,
since it IS the tendency of gases to expand on
heating. The converse is true for a dlmlnutlon
of current; so, If this change of current can be
made periodic, we'll as rapid enough. the
may be made to give out musical note, due
to the fact that the vibratio of the heated gas
will be transmitted as a sound wave to sur
rounding air.
This is the principle made use of in the speak
ing arc, the invention of which was due to
Simon. A telephone transmitter is connected
In series with battery and the primary circuit
of small transformer. The secondary circuit
has its terminals connected each to a carbon of
a direct current arc, which is rather
high voltage, say two hundred and twenty and
is drawn out SO that it g flames" The con-
nectlon IS not continuous, however; but IS
broken by the insertion of condenser. which
refuses to allow the passage of steady current,
but will transmit small alterations or varia
tions. When the transmtter is talked or played
into, feeble alternating current arises in the
secondary transformer circuit, Just as IN the
ordinary telephone wire, and this has the same
periodicity of vibration the voice musical
note. This alternately increases and dirnin-
ishes slightly the main current in the arc, and
gives rise to the sound, explained. Both in
quality and pitch it would be like the original
The extremely small current that arises in
the transformer is rendered more effective by
what termed electrical oscillations"
back and forth surges of current in the circuit
of transformer, condenser, and arc At best,
however the effects still small, and the
temperature changes that arise in the arc are
SO minute that one is tempted to apply the time
honored expression of the importance of small
things Thus. while the arc itself is at a tenn
perature of some sixty-fve hundred degrees
Fahrenheit or more, the computed change of
temperature due to the superposed currents is
hardly single degree. But though the heated
vapor of the arc may be heating and cooling
by only this small amount and undergoing
proportionally minute expansions and contrac-
tions, yet this is sufficient to cause sound
that, as already noted, may be heard by
roomful of people. L. r. IngersoH
A Unique Experiment