John Logie Baird (1888-1946)

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                         THE SPHERE

[MAY 10, 1924

TELEVISION—The Problem of Seeing at a
         Distance—How Near Is It?

[NLS note: a graphic appears here – see image of page]

The Apparatus which Makes it Possible to “See” at
                     Least a Cross by Wireless

[NLS note: a graphic appears here – see image of page]

The Radio Vision Transmitter, by which the Inventor, Mr. L. G. Baird, Hopes to
                         Transmit Pictures by Wireless

The problem of seeing by wireless has been
materially advanced by experiments carried
out by Mr. J. L. Baird, a Scottish inventor,
who has actually transmitted a '' cross ” by
wireless. How this has been accomplished
is described in the article below. The possi-
bility of its development in the future offers
a fascinating prospect.

Many people have heard of the work of an
American and a Frenchman in connection
with radio television. But few know that a
Britisher has, by means of apparatus much more
simple than any yet evolved, achieved what may
seem fantastic to the non-scientific mind. He
has seen by wireless.

In order to accomplish this the inventor first
of all chängës light info sound, transmits that
sound by wireless, and then receives the sound
which by a special piece of apparatus is changed
back into light. This is roughly how it is done:
Light waves and wireless waves travel through the
same medium—ether. It is reasonable, therefore,
to expect to find a connecting link between two
things—light and electricity (which produces wire-
less waves). There is a connecting link, and it is
called a silenium cell. The silenium cell is com-
posed of material which gives forth an electric
current varying in intensity according to the
variations of the light thrown upon it.

It may be well to describe roughly the means
by which Mr. Baird has successfully evolved an
apparatus capable of “seeing by wireless.” The
primary power is a powerful light—an arc lamp or
a very strong electric globe. The light from this
is passed through the object to be transmitted.
Let us suppose this to be a cross. The cross then
is cut out of a solid and opaque material. In the
experimental apparatus used the cross was cut out
of a piece of cardboard.

The light which penetrates through the cut-out
image is focussed through a lens on to a silenium
cell. Between the cell and the lens is a disc
which is revolving at a high speed; in this disc
there are a number of holes punched in series of
fives. The first hole is made on the edge of the
disc, the second a little nearer to the centre, the
third a little nearer still, and so on to the fifth
hole, which, is closer to the centre than any. Then
a fresh series starts, and so on around the whole
of the disc.

The effect of revolving this disc in front of the
image is to allow a certain strip of the image to be
transmitted. Thus eventually the whole of the
picture is transmitted in a series of flashes. But
the speed of the disc is so high that the eye is
deceived, and the whole of the image appears to
be sent at once. In front of this disc is another
which is revolved in the opposite direction on
the circumference of this second disc are a number
of spokes so arranged that they cut across the
flashes of light passed through by the holes in the
first disc.

Light and sound are both vibrations, and light
vibrations are extremely fast; sound vibrations are
much slower. The serrated disc allows flashes of
light to pass at a frequency equivalent to a very
high-pitched note. In fact, if a telephone was,
connected across the silenium cell a shrill scream
would be heard. This in reality would be the
“sound of the picture being transmitted by
wireless.”

The light passed by the image is now thrown
on to a silenium cell. This, of course, is after it
has. passed through the two discs, the second of
which has split the light into variations which the
cell can follow. When light is thrown on to a
silenium cell the cell gives out an electric current.
Thus Mr. Baird has made the link between light
and electricity. These electrical impulses, after
being greatly amplified, are passed into an ordinary
wireless or wire transmitter, and thence broad-
casted in the usual manner.

Now as to the receiving end; if wireless is
being employed, the received impulses are again
amplified. They are then passed to the apparatus,
which will make them visible to the human eye.
This is merely a disc upon which there are a
number of “ quick acting ” electric lamps placed
in positions exactly corresponding to the holes
made in the transmitting disc. These lamps are
all connected to a commutator, and to this
commutator the received impulses are passed.

Now the receiving disc is revolved at exactly
the same pace as the transmitting disc. This is
accomplished by methods, with which it is not
necessary to deal at present, known as syn-
chronising. The lamps therefore light up in
“ sympathy ” with the flashes of light passed by
the transmitting disc, and form the original image
which was transmitted,

That briefly is the.apparatus evolved by Mr,
Baird. Eventually, perhaps, the general public
will be able to sit in a kinema theatre, let us say,
or even in their own homes, and see the events of
the day actually enacted before their eyes !