International projectionist (Oct 1931-Sept 1933)

28 INTERNATIONAL PROJECTIONIST September 1933 Institution in London, transmitted real images of a living human face by electrical means. Progress since that time has been slow and gradual, but none the less effective. There are in the United States today about thirty television stations, some of them operating on regular schedule, and it is estimated that there are about 25,000 receiving sets, mostly in the hands of amateurs. It may be said that television converts light w^aves into electrical impulses for transmission by radio just as the microphone converts sound waves into impulses for similar transmission. The method in use today is indicated briefly: A scanning machine converts the scene or object, which is under the glare of a brilliant light, into an orderly succession of picture elements of a rapidly rotating disk having a number of systematically spaced apertures. The whole field of view is scanned by one complete revolution of the disk and the light waves breaking through the apertures are converted into a sequence of electrical impulses of proportionate intensity by a photoelectric cell. The impulses are then transmitted and received by wire or radio in the same manner as any other signals. Upon reception, they effect the pro portionate amount of light emitted by a lamp of special design, the rays of which are directed through a scanning disk, the duplicate of and operating at exactly the same speed as that in the sending station. Focused on a screen, the light reproduces the original scene in the form of moving pictures. This, in an elemental way, is the process generally used in television today. Some of the steps may vary in different systems and all of them are subject to constant experimentation. Possibly few of them will remain the same by the time television is made available to the average person. Many Obstacles Before television is perfected, there are many obstacles to overcome. Since experimentation is costly and there is no immediate return from the expenditures, research work in many laboratories is being retarded. Some of the larger companies with regular research departments, however, are continuing their work unabated. The seven major problems to be solved, according to Mr. Edwin K. Cohan, technical director of the Columbia Broadcasting System, are: 1. Greater detail of picture, made possible by an improved scanning sys tem that will increase the number of lines far higher than sixty, the present standard. 2. A superior photoelectric cell or "eye," so sensitive that it will "see" scenes in natural light. 3. Increased luminosity at the receiver to project larger pictures in an undarkened room. 4. Removal of the current limitation of transmitting medium by selection of a wave-band in the ethereal spectrum where a wide pathway may be devoted to television. 5. Establishment of wires suitable to carry moving pictures or short waves, so a television network can be organized. 6. A source of light at the receiver that is not dangerous, difficult to handle nor expensive. 7. Design of a practical, simplified, foolproof receiver retailing at a reasonable price. Perfection Necessary The industry is not anxious to introduce receiving sets on the market until a greater degree of perfection is attained. From a curiosity viewpoint, modern television is probably as well developed as the early radio receiving sets, but the value of such curiosity is Important New Books In The Field THEORY OF THERMIONIC VACUUM TUBES FUNDAMENTALS— AMPLIFIERSDETECTORS BY E. LEON CHAFFEE Professor of Physics, Harvard University A thoroush and authoritative treatment of Taeunm tube fundamentals containing much new and hitherto unpublished material. It covers the foundation of the subject fully and should be of high reference value to engineers concerned with any branch of vacuum tube technique. 666 pages, 6x9, fully illustrated. ^6.00 RADIO ENGINEERING BY FREDERICK EMMONS TERMAN Associate Professor of Electrical Engineering, Stanford University Gives a comprehensive engineering treatment of the more important vacuum tube and radio phenomena. The first part is devoted to the theory of tuned circuits and the fundamentals properties of vacuum tubes and vacuum tube applications, in the light of their importance and interest to every electrical engineer. The latter part takes up more specialized radio topics, such as radio receivers and transmitters, wave propagation, antennas, and direction finding, as well as aids to navigation, radio measurements, and sound and sound equipment. 688 page, 6x9, 417 illustrations. ^5.00 RADIO ENGINEERING HANDBOOK Prepared by a staff of 22 specialists. KEITH HENNEY, Editor-in-Chief Associate Editor, Electronics This book makes available to the radio field an engineering handbook measuring up to all the standards of competent authorship, careful and thorough selection of material, and accuracy of presentation, to be found in other McGraw-Hill handbooks in various fields of engineering. Here is a fund of constantly needed reference material covering all fields of radio engineering, from fundamentals to latest practical applications. 583 pages, iVz x 7, 507 illustrations. ^5.00 THE PRINCIPLES OF OPTICS By Arthur C. Hardy, Associate Professor of Optics and Photography, and Fred H. Perrin, Instructor in Physics, Massachusetts Institute of Technology Combines the purely mathematical with the practical treatment of optics, and emphasizes the design of optical instruments. Designed chiefly as a college text book for students of physics, it can also be used as a reference work for specialists in the fields ef illumination, optometry, motion pictures, television, etc. 600 pages, 6x9, illustrated. ^6.00 Order from INTERNATIONAL PROJECTIONIST 580 FIFTH AVENUE NEW YORK, N. Y.