This new instrument has excited considerable interest among telegraph
and telephone men by its exceeding sensitiveness. It is so sensitive
to the passage of an electric current that a battery formed with an
ordinary pin for one electrode and a piece of zinc wire for the other,
immersed in a single drop of water, will give sufficient current
to operate the relay. In practice it has successfully worked as a
telephonic call on the Eastern Railroad Company's line between Nancy
and Paris, a distance of 212 miles, requiring but two cups of ordinary
Leclanché battery.
The instrument consists of two permanent horseshoe magnets, fixed
parallel with each other and an inch apart. A very thin spool or bobbin
of insulated wire is suspended, like the pendulum of a clock, between
these permanent magnets, in such a manner that the bobbin hangs just
in front of the four poles. A counterpoise is fixed at the top of the
pendulum bar, which permits the adjusting of the antagonistic forces
represented by the action of the swinging bobbin, and two springs, which
are insulated from the mass, and which form one electrode of the local
or annunciator circuit, while the pendulum bar forms the other.
It will be easily understood that as the bobbin hangs freely in the
center of a very strong magnetic field (formed by the four poles of the
two permanent magnets), the slightest current sent through the bobbin
will cause the bobbin to be attracted from one direction, while it will
be repelled from the other, according to the polarity of the current
transmitted.
As the relay has a very low resistance, it is evident that it will
become an acceptable auxiliary in our central office, particularly when
used as a "calling off" signal, as by its use the ground deviation, so
objectionable and yet so universally used for "calling off" purposes,
can be entirely avoided, and the relay left directly in the circuit, as
is being done here in Paris. R. G. BROWN.
Paris, September 12, 1882.
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