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281
Heroes of the Telegraph
·
John Munro
248
If
now
the
slightest
mechanical
jar
be
given
to
the
wooden
frame
of
the
microphone,
to
the
table,
or
even
to
the
walls
of
the
room
in
which
the
experiment
takes
place,
a
corresponding
noise
will
be
heard
in
the
microphone.
By
this
delicate
arrangement
we
can
play
the
eavesdropper
on
those
insensible
vibrations
in
the
midst
of
which
we
exist.
If
a
feather
or
a
camel-hair
pencil
be
stroked
along
the
base-board,
we
hear
a
harsh
grating
sound;
if
a
pin
be
laid
upon
it,
we
hear
a
blow
like
a
blacksmith's
hammer;
and,
more
astonishing
than
all,
if
a
fly
walk
across
it
we
hear
it
tramping
like
a
charger,
and
even
its
peculiar
cry,
which
has
been
likened,
with
some
allowance
for
imagination,
to
the
snorting
of
an
elephant.
Moreover
it
should
not
be
forgotten
that
the
wires
connecting
up
the
telephone
may
be
lengthened
to
any
desired
extent,
so
that,
in
the
words
of
Professor
Hughes,
'the
beating
of
a
pulse,
the
tick
of
a
watch,
the
tramp
of
a
fly
can
then
be
heard
at
least
a
hundred
miles
from
the
source
of
sound.'
If
we
whisper
or
speak
distinctly
in
a
monotone
to
the
pencil,
our
words
will
be
heard
in
the
telephone;
but
with
this
defect,
that
the
TIMBRE
or
quality
is,
in
this
particular
form
of
the
instrument,
apt
to
be
lost,
making
it
difficult
to
recognise
the
speaker's
voice.
But
although
a
single
pencil
microphone
will
under
favourable
circumstances
transmit
these
varied
sounds,
the
best
effect
for
each
kind
of
sound
is
obtained
by
one
specially
adjusted.
There
is
one
pressure
best
adapted
for
minute
sounds,
another
for
speech,
and
a
third
for
louder
sounds.
A
simple
spring
arrangement
for
adjusting
the
pressure
of
the
contacts
is
therefore
an
advantage,
and
it
can
easily
be
applied
to
a
microphone
formed
of
a
small
rod
of
carbon
pivoted
at
its
middle,
with
one
end
resting
on
a
block
or
anvil
of
carbon
underneath.
The
contact
between
the
rod
and
the
block
in
this
'hammer-and-anvil'
form
is,
of
course,
the
portion
which
is
sensitive
to
sound.
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