International projectionist (Jan-Dec 1939)

FOREST 'TOP VALUE' ALWAYS Forest Rectifiers are more than just a collection of features! They are designed for motion picture projection and are built to 'take it'! Priced to enable more exhibitors and projectionists to own real protection and economy. There is a Forest Rectifier for every purpose. All Forest Products! • FOREST Thermionic Rectifying Tubes, tyz-K amperes. Built to rated capacity, with high safety factor. Guaranteed Performance. • FOREST Low Intensity RectiBers. Type LD 15-15 DC amperes and Type LD 30-30 DC amperes. • FOREST Bulb Rectifier for Suprex, Simplified High Intensity or Low Intensity projection. Type LD 60—3 phase, 220 volts, 30-60 DC amperes. • FOREST Magnesium-Copper Sulphide Rectifiers. Designed for Suprex or Simplified High Intensity projection. 5 models — 30 to 100 DC amperes, all for 3 phase operation. Using exclusively the P. R. Mallory rectifying units. Made in the Forest "Twin" models. Authorized Forest Distributors in All Key Cities Forest M.C.S.'S es B ^ : "Twin" Rectifier ril|\[ J I vdctifieK UudfiMtM tinceim \w\n\w RECTIFIERS parative low cost. Tests indicated good reproduction for more than 1,000 playings, however, any needle's life is dependent on such varying and uncontrollable factors as weight and type of pickup, age and condition of records, etc. •NEW LIGHT-SPEEDOMETER WHAT is believed to be the most accurate speedometer in the world, which automatically measures the speed of light, fastest thing in the universe, traveling at the rate of 186,000 miles a second, was announced at Harvard University, and reported in The New York Times, from which the following information was taken. This new light-speedometer was described as the first that does not require visual observation by the human eye and that eliminates friction as a possible source of error. It can measure the velocity of light, it was stated, with an error of less than 2Y2 miles a second, and therefore is believed to be capable of giving the most accurate measurements of the speed of light ever made. The device does its work by "crimping" the light beam to be measured with what may be described as "permanent waves" 19,200,000 of such waves a second. The equipment has been put to work on one of the basic problems of modern physics and astronomy, namely, whether the speed of light is actually constant under all conditions or whether it varies. Self-Measuring of Light Although many important theories, including the theory of relativity, are based on the assumption that the velocity of light is constant, recent new measures have indicated that it may vary under certain conditions. Should this be established, it may call for important modifications of the relativity theory and its consequences. In contrast with the large size of some types of light-speedometers, which utilize long outdoor tubes, the apparatus is contained in a small laboratory room and hallway. With the equipment four separate measures of the speed of light can be made a minute. The basic principle of the device is to impose a wave-form on a light beam in such a way as to compel the light to help in the measurement of its own speed. The beam originates in a high-power 1,000-watt projection lamp. It passes first through a tube which modulates the beam at a frequency of 19.2 megacycles. In other words, the beam is made to fluctuate between bright and dim intensity 19,200,000 times a second. Modulation of the light beam at the high frequency is controlled by a standard frequency generator. With the frequency of the manufactured light waves known, the main problem is to determine the exact length of the waves. The fluctuating beam is split in two by a small sheet of glass held at an angle across the light path. One side of the beam is sent off, up and down a hallway system of mirrors, until it has traveled a distance of about 185 yards. The distance is fixed and has been measured with an accuracy of one part in 200,000. The other half of the beam is sent over a shorter path, about two yards long, whose length is slowly varied during the velocity measurement. Each half of the beam has the same wave-form, or light to dark fluctuations, as the original. DEFECTIVE HEARING FILM "Life Begins Again," movie produced and distributed' by W.E. illustrates how many of the more than 15,000,000 Americans suffering from hearing deficiencies can be enabled to hear again. The picture dwells How Many? Was this copy dog-eared when it came to you? How many men read it ahead of you? You would receive a clean, fresh copy if you had a personal subscription — and you wouldn't have to wait — you would be first to read it. Use coupon below. INTERNATIONAL PROJECTIONIST, 580 Fifth Ave., New York, N. Y. □ 1 year— 12 issues— $2.00 D 2 years— 24 issues— $3.00 Foreign: Add 50c per year. Enter my subscription for Name Address City ... State 26 INTERNATIONAL PROJECTIONIST