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BELL SYSTEM TECHNICAL JOURNAL 



in decade steps from 100,000 cycles to 10, all controlled by the 100,000- 

 cycle primary oscillator. 



The 1,000-cycle motor is geared to a clock in such a way that, 

 when the controlling frequency has its nominal value exactly, the 

 clock keeps accurate time. In order to check the frequency of the 

 system, therefore, it is only necessary to observe changes in rate of 

 the clock so controlled. 



An error of 0.864 second per day in the rate of the clock corresponds 

 to an error in the frequency controlling it of one part in 100,000. 

 It is possible to check the rate of the clock visually with an accuracy 

 of about 0.2 second from audible time signals but obviously this is not 

 sufficiently accurate for our purpose, giving an accuracy of only about 

 one part in 400,000 in a day's observation. In order to facilitate the 



Fig. 14 — Circuit of submultiple generator. 



comparison with time signals, a contact operated by a cam driven by 

 the 1,000-cycle synchronous motor makes a contact once each second, 

 or to be exact, once for each 100,000 cycles of the primary oscillator. 

 This contact operates one element of a two element recorder while 

 time signals operate the other. Comparisons may thus be made by 

 actual measurements on tape and can be made with greater accuracy 

 than can be judged by eye. 



The 1,000-cycle synchronous motor, with its two generators and 

 induction starting motor geared to the clock, is shown in Fig. 15. 

 In this figure the seconds contact mechanism may be seen on the 

 vertical shaft intermediate between the shaft of the motor and the 

 second-hand shaft of the clock. 



The assembled rotor of this motor is shown in Fig. 16. The large 

 disc is the 1,000-cycle motor rotor. The disc below it is a hollow 

 steel flywheel filled with mercury used to reduce hunting. The small 



