A HIGH PRECISION STANDARD OF FREQUENCY 



513 



through the primary of an induction coil, which discharge produces a 

 spark across the gap below the circular scale. The portion of the 

 scale illuminated by the spark is photographed on slowly moving 



4-'---''-t- 



o 

 o 



0| - OSCILLATOR 100,000.0 CYCLES. 

 O4- OSCILLATOR 100,0001 CYCLES. 

 S- CIRCULAR TRANSPARENT SCALE. 

 G- SPARK GAP. 



A- FILM ADVANCING DEVICE. 

 R- RELAY 



SMG-SUBMULTIPLE GENERATOR. 

 BFI- BEAT FREQUENCY INDICATOR. 



Fig. 22— Circuit of device for determining beat periods accurately. 



film at ^. In this manner, assuming a beat frequency of 0.1 cycle 

 per second, 360 checks per hour may be obtained with practically no 

 supervision. 



*-* 



Fig. 23 — Apparatus used for measuring beat periods. 



If the sparks occur at exactly an even number of revolutions of the 

 motor apart, the same portion of the scale will be photographed by 

 each spark. If the intervals dififer from such a value by 0.001 second, 

 the successive photographic images will dififer by one scale division. 



