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The master fork consists of a specially mounted steel tuning fork, vibrations of which are sustained by magnetic pulses from the two lower pairs of magnets. The vibrating fork induces electric impulses in the upper pairs of magnets. These are amplified by the two vacuum tubes at the left and delivered to the driving magnets in the proper phase to keep the fork vibrating. The vacuum tube at the right delivers impulses to any desired external circuit

ANOTHER USE FOR THE VACUUM TUBE

THE master fork shown in the accompanying photograph maintains its rate of vibration at 60 cycles per second to within two parts in ten thousand. This high order of frequency stability is attained by te use of vacuum tubes, which derive excitation impulses from the vibrating fork without introducing their own circuit characteristics. The fork is, therefore, the sole frequency-determining element in the electro-mechanical system.

Impulses from this master fork control smaller slave forks which in their turn drive synchronous motors. Since the frequency of the fork is practically constant, the angular velocity of the motors is constant. The motors would, therefore, make highly reliable standards of time if they were made to drive clock trains.

You are cordially invited to visit the General Radio Company's engineering laboratories the next time you are in Cambridge. Let us demonstrate some of the engineering apparatus that will help you with your own industrial problems.

GENERAL RADIO COMPANY
Manufacturers of Standard and Special Apparatus for Both Laboratory and Industrial Uses
CAMBRIDGE A. MASSACHUSETTS