Чтение общенаучной литературы. Кытманова О.А. - 23 стр.

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24
TELEVISION.
The word television comes from the Greek word tele, meaning "far", and the Latin
word visio, meaning "sight". Thus television really means "seeing at a distance".
The first television pictures were publicly demonstrated in 1926 by John Logie
Baird, a Scots engineer. At first the images were tiny and flickering but Baird
gradually improved them. Among rival systems was a Marconi-EMI system, which
operated electronically instead of using the mechanically rotating disks of the
Baird apparatus. (Details of the development of television broadcasting in various
countries , throughout the world can be found in the article BROADCASTING.)
Making the Pictures
The first problem in television is to change the light reflected from a scene in the
studio or elsewhere into another form — one that will travel long distances,
penetrate solid objects, and go round corners. Electric currents will do all these
things and there are ways of converting light into electricity. The second problem
is how to use the electric currents to control a light source at the receiver in such a
way that an image of the original scene is recreated.
The article PHOTOELECTRIC DEVICE explains how certain substances alter
when exposed to light. These substances can be made into* devices that will
change light of varying intensity (brilliancy) into electric currents of corresponding
strength.
If we merely place a photoelectric device in front of the scene, the current
produced will represent no more than the average amount of light reflected. There
will be no information as to the nature of the picture, nor as to which parts should
be light and which dark.
This difficulty can be overcome by dividing the scene into small parts and
presenting these to the photoelectric device one by one. The simplest (but not the
best) way of doing this is to use a rotating shutter consisting of a disk with holes
drilled through it in a spiral pattern. If this shutter is placed between the scene and
the device, the holes as they rotate expose one small part of the picture after the
other. For each exposure the device will produce a pulse of electricity proportional
to the light received. This method of scanning, 3s the process is called, was used
by Baird and had been invented by Paul Nipkow, a German engineer, in 1884. The
modern method is to use a surface coated with light-sensitive material. The first
man to make a workable device of this kind 'which we now call a camera tube) was
Vladimir Zworykin, a Russian-born physicist. He patented his iconoscope (as he
called it) in 1923, hut it was so difficult to make that he was unable to demonstrate
it until 1929. Modern systems operate on the principles used in the iconoscope,
although great improvements have been made.
One form of camera tube is a glass cylinder, from which air has been removed,
mounted inside the camera casing. The image of the scene being televised is
focused by lenses on to the flat glass wall forming one end of the cylinder. Inside
this wall is a transparent coating of electrically conductive material, called the

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