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281
Heroes of the Telegraph
·
John Munro
245
The
imperfect
contact
between
the
broken
ends
of
the
wire
proved
itself
to
be
a
means
of
transmitting
sounds,
and
in
addition
it
was
found
to
possess
a
faculty
which
he
had
not
anticipated--it
proved
to
be
sensitive
to
very
minute
sounds,
and
was
in
fact
a
rude
microphone.
Continuing
his
researches,
he
soon
found
that
he
had
discovered
a
principle
of
wide
application,
and
that
it
was
not
necessary
to
confine
his
experiments
to
wires,
since
any
substance
which
conducted
an
electric
current
would
answer
the
purpose.
All
that
was
necessary
was
that
the
materials
employed
should
be
in
contact
with
each
other
under
a
slight
but
definite
pressure,
and,
for
the
continuance
of
the
effects,
that
the
materials
should
not
oxidise
in
air
so
as
to
foul
the
contact.
For
different
materials
a
different
degree
of
pressure
gives
the
best
results,
and
for
different
sounds
to
be
transmitted
a
different
degree
of
pressure
is
required.
Any
loose,
crazy
unstable
structure,
of
conducting
bodies,
inserted
in
a
telephone
circuit,
will
act
as
a
microphone.
Such,
for
example,
as
a
glass
tube
filled
with
lead-shot
or
black
oxide
of
iron,
or
'white
bronze'
powder
under
pressure;
a
metal
watch-chain
piled
in
a
heap.
Surfaces
of
platinum,
gold,
or
even
iron,
pressed
lightly
together
give
excellent
results.
Three
French
nails,
two
parallel
beneath
and
one
laid
across
them,
or
better
still
a
log-hut
of
French
nails,
make
a
perfect
transmitter
of
audible
sounds,
and
a
good
microphone.
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