John Logie Baird (1888-1946)

TELEVISION

AUGUST 1928

    Recent Advances in Television

  Television by Daylight and Television in Colours

                                       By The Editor

In this article you will read many things of interest on the recent developments in
television, now known as Television by Daylight and Television in Colours. Having
been present at both demonstrations the Editor is in the happy position of being able
                    to touch upon these advances in an authoritative way.

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

Mr. Baird demonstrating daylight television reception to a group of scientists
                                 and press representatives.

THE possibility of transmitting
television in colour has been
visualised for some consider-
able time by those intimately con-
nected with television developments,
but this advance was only achieved
practically on July 3rd, 1928, when,
by employing a three-colour process,
Mr. Baird was able to demonstrate
the transmission of images in their
natural colours.

This process is extremely inter-
esting, and is essentially very similar
to the process employed in one of
the forms of colour cinematography.
It consists in presenting to the eye,
in rapid succession, first a green
image, then a blue, and then a red
image.

These three colours form the
well-known primary colours, from
combinations of which any other
colour or tint may be obtained: for
example, purple is a mixture of
red and blue, yellow is a mixture
of green and red, and all other
colours excepting the three primaries,
red, green and blue, are in a similar
way composites of these three colours
in varying proportions. When the
three colours are combined together
they give to the human eye an
impression of white.

The actual mechanism used in
these first experiments consisted of
a disc perforated with three spirals
of holes arranged consecutively
round the disc. (See Fig. I.) This disc
was used in conjunction with the
light spot system which has already
been described in the pages of this
journal. By using a disc with
three sets of perforations it was
possible to traverse the image firstly
with a blue spot of light, secondly
with a red spot, and thirdly with a
green spot, the perforations being
covered with blue, red and green
light filters.

    Points on the Neon Tube.

The operation of this mechanisrn,
therefore, caused the light-sensitive
cells to transmit first a picture which
showed only the blue parts o£ the
scene, then a picture showing only
the red parts of the scene, and lastly
a picture showing only the green
parts of the image.

At the receiving station a similar
disc was used, the three sets of
perforations, or spiral apertures, being
covered by blue, red and green
filters respectively in a fashion
similar to those at the transmitter.
The difficulty at the receiving station,
however, was to find a light source of
generating blue, red and green rays.

The neon tube which has hitherto
been used for reception, while exceed-
ingly rich in red rays, has practically

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

                            Fig. 1.
The spiral disc used for colour television.

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