Our information is derived from this article and from
others by M. Hospitalier.
The method previously adopted by Van Rysselberghe, to prevent
induction from taking place between the telegraph wires and those
running parallel to them used for telephone work, was briefly as
follows: The system of sending the dots and dashes of the
code--usually done by depressing and raising a key which suddenly
turns on the current and then suddenly turns it off--was modified so
that the current should rise gradually and fall gradually in its
strength by the introduction of suitable resistances. These were
introduced into the circuit at the moment of closing or opening by a
simple automatic arrangement worked exactly as before by a key. The
result, of the gradual opening and gradual closing of the circuit was
that the current attained its full strength gradually instead of
suddenly, and died away also gradually. And as induction from one wire
to another depends not on the strength of the current, but on the rate
at which the strength changes, this very simple modification had the
effect of suppressing induction.
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