TELEVISION.

Hawera Star, Volume XLV, 1 October 1925, Page 8

TELEVISION.

PICTURES BY WIRELESS. EXTENSION TO KIN EM A. _ s The transmission of still pictures by t wiie is in commercial use to-day, t writes the ' New' Y ork correspondent pi j the Manchester Guardian. There are ■ several systems which could. send still _ pictures by wire or radio. The Process j lor moving pictures < from that tor still pictures or lantern •( slide pictures only in the speed ol the , presentation of each distinct image of j the series. That is, a moving pictuie, to give the illusion of continuity, miist ( have its image changed twelve .to six- ( teen times a second. Briefly, any system for sending a . picture electrically from one point to . another calls for three necessary elements —(1) some means for translating the lights and, shades of the picture 'into some form of electric current, (_). an electrical medium which will transmit the characteristics of the electric current correctly to a distance, and (3\ a hie an s at the receiving end tor retranslating the electrical signal back into lights and shades corresponding in values and positions with those of the original picture. Analysed for transmission purposes, a picture is made up of a large number of small elements or lines varying in light and shade ' The transmission of an entire picture requires some method whereby these elements are traversed or covered a hit at a time. At the receiving end these elements are finally reproduced, element by element, on a photographic film, in time are grouped together, and finally build up a reproduction of tlie original picture. Difficulties must be overcome m order to send moving pictures, since the transmission has to be enormously speeded up. for instance, a still picture with a fineness of 100 lines to the inch might be transmitted in four o'r five minutes, with the time divided amoiu- the 100 lines. A motion picture, 'however, would require an entire frame or single picture of the series to be transmitted in one-sixteenth ol a . second, and any attempt at such fineness of, detail as 100 lines per inch calls for a. tremendous increase of speed of all the units used, in the system, or several thousand times that required for still pictures. in the Jenkins system the transversing or tracing of the pictuie. is done bv a revolving prismatic disc, which causes a beam of light passing through it to oscillate on one side, thus travelling over the entire picU The converting of the light and shade of the picture into electric currents is done by means of a lightsensitive cell. The rotating prism causes a picture image to move over the light-sensitive cell, so that every line or element of the picture is focussed on the cell. The changing tio'ht teams cause a similar fiuctuatjncr electric current to flow' from the : licrht cell; it is impressed on a radio transmitter and modulates the carrier wave, which may be thought of as a continuous stream of electromagnetic waves 'which, travel across the space between stations. The necessary speed tor motion pictures has, so t;ir as.ieia.tes to the optical and mechanical means, been obtained by Mr. Jenkins by revolving a plurality of lenses spaced around the outer circumference ol : a disc prism, which multiplies the tracing effect of the beam of light on the picture surface, yet permits the glass" prism to rotate at a safe rate of speed. . . ~ Jenkins uses for a receiving unit an extremely sensitive glow-lamp or gas-filled lamp. This is brought up to a. dull glow by a local battery, and the incoming amplified signal is impressed upon it, which causes it tc increase or change its brightness in step with the light values of the different parts of the picture at the send- . ing station. A disc, around which are placed lenses in number equal to those oi the transmitting station, is revolved in synchronism with tho transmitter rotating lens referred to before, which slices the picture at the sending station into a number of lines. In a similar manner, and in step, the Revolving lens at the receiving station continually projects the fluctuating light on "to a ground glass screen. Tho light appears there in the form of consecutive lines, agreeing with the original, and being in correct position these form an image of the original pictuie. The tracinrr of the picture line is done so rapidly that, of course, it appears on the screen to the eye as a complete picture of the series. In other words, for comparison, the unit of the ordinary moving picture is a single frame of the series. In wirelessed - moving pictures the unit is a single line of a single frame. The picture is cut up into lines for sending, and the received lines are flashed together to reform the frame on the screen.