Television

Some success has been achieved in using the image signals themselves to control synchronization, whereby separate syn chronizing circuits are avoided. Another means of securing synchronization is presented where all the receiving stations and the sending station are on the same alternating current power or lighting system. It is then only necessary to operate the receiving sets on suitable synchronous motors. This kind of synchroniza tion, because of the low frequencies (usually 6o cycles) used and the relatively wider tolerances for power purposes, as compared with ideal television requirements, is apt to call for occasional correction by hand adjustment of the image position. With the continually increasing practice of operating city and other large area public service electrical supplies in synchronism for clock control and other purposes, this method of regulating the speed of television apparatus appears of practical promise.

Applications of Television.

A number of applications of television are suggested by considering parallel cases in sound transmission. Iri sound we have the use of the telephone for con versation between individuals, the use of loud speaking systems for carrying speeches to large audiences, and finally, broadcasting equipment for transmitting voice or music to home receiving sets. We can similarly imagine television to be used in connection with the telephone, for displaying public speakers or athletic events to audiences at a distant point (see Plate, fig. I), or for the broad casting of scenes into homes. At the present time (1931), while all of these possibilities as well as some special developments, such as television in color, have been experimentally demon strated, the practical and economic barriers to really satisfactory images are so great as to oppose very serious obstacles to the general use of television.

Probably the most completely worked out phase of television is its use as an adjunct to the telephone, although this has been done only on an experimental basis. Here the image to be trans mitted—the human face—requires only a number of image ele ments which can be handled satisfactorily by existing practical signal generating and transmitting apparatus. In a demonstra tion installation for two-way television in conjunction with speech in New York the American Telephone and Telegraph Company uses two booths, located in two of their buildings, several miles apart. Two scanning discs are used at each booth, one for beam

scanning, the other for viewing the neon lamp. Telephone instru ments, which would interfere with vision of the face, are not used, but in their place is a system of concealed microphones and loud speakers. The two parties to the conversation talk to and see each other as though sitting on opposite sides of a table. An image of 4,400 elements is used, which reproduces facial expressions quite adequately. In order, however, to carry the two sets of television signals, the telephone currents and the synchronizing signals, transmission facilities are used which in present telephone practice could otherwise carry fifteen telephone conversations.

The radio broadcasting of television for entertainment pur poses is still in an experimental stage, with no clear answer as yet whether television may ultimately be expected to compare in value with sound broadcasting. Regular television programs have been broadcast for some time by the Baird Television Company in England, and by several stations in the United States, most of the latter transmitting from motion picture film. In all cases the number of image elements is small, from 3o to 6o scanning holes being used, with a consequent restriction to very simple objects such as one or two faces. While this limitation to coarse grained images is in part set by the state of development of the television apparatus itself, it is also governed by the radio bands available. In the United States several bands of Ioo kilocycle width have been set aside by the Radio Commission for "experimental" tele vision. It is recognized that the entertainment value of images which can be transmitted over such bands is small, but on the other hand the demand for ether space for ship, airplane and other radio services is such that wider bands will be increasingly difficult to obtain. Television images containing the wealth of detail of the motion picture film, which may be taken as the goal of television broadcasting, demand complexity of apparatus, and transmission facilities, far beyond anything now in prospect. Whether a working compromise will be attained in which the value of the simultaneity of event and viewing, which is the essence of television, will be great enough to offset the crudity of a commercially possible picture, is for the future to disclose.

(H. E. I.)