TELEVISION PROMISED

Hokitika Guardian, 20 September 1929, Page 8

TELEVISION PROMISED

A MARVEL OF TELEGRAPHY. The Postmaster-General (the Hon. J. B. Donald) speaking at a ceremony in Christchurch on Saturday to mark the change over in that city from the manual to the automatic telephone system said a television plant would shortly be working between Auckland and Wellington, and that in due time there would be a service linking up the four main centres.

No word lias been received in Auckland of this impending installation bj the Department, but in view of the fact the television is now in operation between Sydney and Wellington, and New Zealand specially prides itself in keeping up to date in the Post and Telegraph Departmont, the fact announced by the Minister does not surprise technical people at this end.

Television is the invention of a young Scottish engineer named J. L. Baird, but it was first brought into the range of practicability in, the United States. The first demonstration took, place in Britain, in 1926, when the members of the Royal Institution were given an opportunity to see the results of fifteen years’ hard, work on the part of Mr Baird. A year later the tiling was being taken up in the United States with characteristic enthusiasm, and there was much interest in scientific circles when, in April, 1927, television triumphed on the occasion of its first demonstration between Washington and New York.

Although almost uncanny in its results television is so purely -mechanical, tnat people who' have seen a demonstration say it is really just as simple as wireless as far as the layman is concerned.

The process begins when the sitter takes his position in front of the television apparatus and the arc light is turned on. Most of the light, Is shut, off from the sitter by a disc. In the disc are a series of holes. As the disc is turned the light strikes the sitter tnrough the hole nearest the rim. This spot of light travels across the sitter’s face, just below the first, the third just below the second, and so on. There are a total of 50 holes, and 50 spots of light travel across tne sitter—or the scene to be photographed—one below the other. If the process could be slowed down infinite.y, if would begin with the action of tne visible spot of light. In practice, however, the spots move so quickly that the subject seems to be flooded by a steady illumination. There is never more than one spot of light on his face at a time, but the entire 50 spots cross the face or thing to be photographed 18 times a second.

SPOTS OF LIGHT. I The lines and contours and colours of the face cause variations in the brightness of the spots they reflect. These variations are turned into variations electrical i current. Facing the sitter are three large photo-electric cells. Th® moving spots, of light are reflected from the face or scene into these cells, where the ycause electron showers. The showers are strong or weak, as the light is strong or weak. Electron showers are nothing but electrical cm rent, so that these cells cause a current which constantly varies according to the characteristics of the face or scene to be pictured. This current is amplified 5,000,000,000,0i,0,000 times before it is strong enough for the work required. Then it is sent, either by wire or radio, to the receiving television station. This current is a flying picture. Every change in volume is a feature of a scene or portrait. But the question is to make every bit of this flying picture .land in the right place.

Arriving at the receiving apparatus, the current is carried to a “brush” or an electrical contact apparatus, which is mounted on a wheel. As it revolves on this wheel,- the “brash” makes and breaks electrical contact approximately 2500 times. Each contact is made with one of the 2500 wires which are mounted on a circle in which the wheels turns.

Each wire snatches a bit of the electric current of flying picture. To each one of these wires must be delivered 18 times a second exactly tlie same bit of the picture which is intended for it. The most minute error would scramble the portrait completely.

USE OF NEON GAS. Each wire carries its bit of current to a square of tinfoil behind the television screen. These squares of tinfoil are arranged 50 in a row. There are 50 rows. When the hit of current —or fragment of picture—reaches one square of tinfoil it leaps from the tinfoil to a wire. It makes the leap through the gas called neon. This is instantaneously illuminated by the passage of electrical current through it. Eighteen times a second there is a flash of neon in front of each of the 2500 patches of tinfoil. 'Hie flash is strong or feeble, according to the light or shadow on one particular part of the face or scene. These tiny flashes-f----occurring at the rate of about 45,000 a second—build up the face o’n the screen.

The receiving and transmitting of the picture—that is, the taking to pieces of the picture at one place and its reassembled at another—is synschonised by a special system which causes every one of the 2500 squares or unit to fall in its proper place -8 timbs a second. This control involves the use of two wires. In the case of radio television one, wave-length is used for sending the picture, and 'two for the Synronisation process,