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281
Heroes of the Telegraph
·
John Munro
231
Among
Edison's
toys
and
minor
inventions
may
be
mentioned
a
'voice
mill,'
or
wheel
driven
by
the
vibrations
of
the
air
set
up
in
speaking.
It
consists
of
a
tympanum
or
drum,
having
a
stylus
attached
as
in
the
phonograph.
When
the
tympanum
vibrates
under
the
influence
of
the
voice,
the
stylus
acts
as
a
pawl
and
turns
a
ratchet-wheel.
An
ingenious
smith
might
apply
it
to
the
construction
of
a
lock
which
would
operate
at
the
command
of
'Open,
Sesame!'
Another
trifle
perhaps
worthy
of
note
is
his
ink,
which
rises
on
the
paper
and
solidifies,
so
that
a
blind
person
can
read
the
writing
by
passing
his
fingers
over
the
letters.
Edison's
next
important
work
was
the
adaptation
of
the
electric
light
for
domestic
illumination.
At
the
beginning
of
the
century
the
Cornish
philosopher,
Humphrey
Davy,
had
discovered
that
the
electric
current
produced
a
brilliant
arch
or
'arc'
of
light
when
passed
between
two
charcoal
points
drawn
a
little
apart,
and
that
it
heated
a
fine
rod
of
charcoal
or
a
metal
wire
to
incandescence--that
is
to
say,
a
glowing
condition.
A
great
variety
of
arc
lamps
were
afterwards
introduced;
and
Mr.
Staite,
on
or
about
the
year
1844-5,
invented
an
incandescent
lamp
in
which
the
current
passed
through
a
slender
stick
of
carbon,
enclosed
in
a
vacuum
bulb
of
glass.
Faraday
discovered
that
electricity
could
be
generated
by
the
relative
motion
of
a
magnet
and
a
coil
of
wire,
and
hence
the
dynamo-electric
generator,
or
'dynamo,'
was
ere
long
invented
and
improved.
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