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April, 1939 J 1939 SPRING CONVENTION 471
being selected primarily on the basis of proved operating reliability over long periods of time.
The apparatus is a twenty-ton magnification of the call announcer, the first model of which is satisfactorily operating in telephone plants after nine years of continuous service. The Poly rhetor consists essentially of a rotating steel drum eight feet in diameter, machined to watch-like precision, capable of carrying 24 continuous film loops past 168 optical scanners and associated amplifiers mounted on seven posts equally spaced about the drum. A multiple system of sectionalized trolleys conveys the sound through sliding contactors to small speakers in the cars, around which sufficient acoustical partitioning is provided to avoid program interference from car to car.
This project presented many problems unique in sound equipment design and their step-by-step solution is briefly discussed.
"Simplifying and Controlling Film Travel through a Developing Machine;" J. F. Van Leuven, Fonda Machinery Co., Los Angeles, Calif.
A developing machine is described in which the drive of the film is frictional and the film-carrying rollers are driven on the slack of the film. The first driving roller is slightly smaller in diameter than all succeeding driving rollers, thereby setting up a tension on the film throughout the machine.
The upper shaft of film-carrying rollers is held in peripheral engagement with the driving rollers by adjustable springs which have a mounting that is yieldable downward so that any excess tension on the film draws the film-carrying rollers away from the driving rollers until the excess tension has been relieved, which allows the film-carrying rollers to be drawn upward by the springs to contact the driving rollers again.
The driving rollers are directly over the upper film-carrying rollers. The driving mechanism is completely above the tanks and solutions, and all filmcarrying rollers in the wet end are mounted individually free and, in turn, are all mounted on free-turning tubing or shafting.
Film-carrying rollers in the dry box, in addition to being mounted on Arguto bushings and individually free, are mounted on tubing which in turn is mounted with grease-seal ball-bearings on shafting, the entire unit being free to rotate or to slide laterally on the shaft, thus becoming self aligning.
To meet the high initial and maintenance cost of ball-bearings found in filmcarrying spools, 7V4-inch film-carrying rollers are used throughout.
Film enters machine in a steady, constant flow. Tension can be altered by the operator and, when regulated by adjustment of springs, remains virtually constant throughout the machine. The steady flow makes great speed possible and yet retains a high factor of safety. The machine has the following attributes: great simplicity; entire freedom from precision maintenance; film is always under even adjusted control and does not slip on rollers; breakage from mechanical causes is practically eliminated.
"A Reel-and-Tray Developing Machine;" R. S. Leonard, Municipal Light and Power System, Seattle, Wash.
A reel-and-tray film-processing system of 7 to 200-ft. capacity, designed to overcome deficiencies in existing small-scale film-processing equipment, is de