The Wilmington morning star., 1944-05-14

from wax disks into which it has
been scratched by vibrating
needle. You have heard sound
coming from motion picutre film
on which it has been photographed
by varying beam of light.
You may NOT yet have heard
sound reproduced from hairfine
steel wire on which it has been
recorded by magnetism.
Today magnetic wire recording
- sound on wire" - is busy
gathering military intelligence for
the Allies. 1t is under fire in ieeps
and foxholes on invasion beaches,
in submarines close to Tokyo and
in bombers over Berlin. Tomor
row it will be put to hundred
civilian uses that have b eer
thought up for it.
Strangely inc princirle of mag
netting wire which now promises
a revolution in sound recording lay
dormant for 40 years after it's dis
covery in 1898 Through the era Of
Bell, Edison and Steinmetz its
technical kinks went uniroaed.
The world leaped forward in
knowledge of sound and electricity
but waited for a physicist to be
born, to grow up and to turn the
recording wire 80 degrees SO as to
parallel instead of cross the mag
netic field. The story is summarize
ed in bulletin of the National
Geographic Society
Valdemar Poulsen. Danish scien-
tist, in 1898 applied telephone
engineering in translating III e
waves of which all sound is COM
posed into waves of electric cur
rent in copper wire. Wrapping the
wire around an iron core he in
duced in the core a magnetic field
which likewise varied with the
sound
Poulsen's next step and great
contribution to sound recording
was to move a thick steel wire
continuously in one direction across
the varying magnetic field. He
thus spotted tiny magnets repre-
senting the varying sound in a
crosswise position along the NOV
ing wire. By reversing the several
steps he re-created the sound.
The sound became jumbled
however when the round wire
twisted. Even slight twisting turn
ed each crosswise-recorded magnet
away from it's position necessary
for good reproduction. The twist
was conquered by using flat steel
tape instead of round wire. But
tape proved unwieldly and tape
recording ran a poor second over
the years in competition with wax
cylinders and disks.
Studying Poulsen's recording
method a present-day physicist in
the late 1905 reasoned that if
the sound-induced magnets could
be spotted lengthwise instead of
crosswise along the moving wire,
twisting would not affect reproduce
ton and hair-thin wire could be
used for compactness.
To accomplish this purpose a
half-hair' s-breadth gap was made
across the field of the magnetized
core. A hair s-breadth wire was
run parallel to the field in the
core instead of perpendicular to
it - separated from the core
by less distance than the half-hair
breadth of the gap.
AS the fine wire moved past
the gap the sound-induced magne-
tism - following path of least re-
sistance - jumped for an instant
to the moving wire then back to
the core beyond the gap. Thus it
made on the wire lengthwise
magnetic record of the sound.
Success of the new method
brings sound-on-wire close to per-
lection. Planes tanks ships and
submarines are gradually being
equipped with compact portable
magnetic wire recorders and re-
corder-reproducers which civilians
will welcome after the war. They
faithfully record every detail of
sound at the war fronts.
Recorders alone weigh only eight
pounds including a half-pound of
steel wire which is over two miles
long and records AZ y,oip,,+e. ~