578 BELL SYSTEM TECHNICAL JOURNAL 



negative voltage, ^ ^ . While the contact is closed, the battery E^, with 



resistance R^ in series, is short-circuited. But at the instant of opening the 

 contact, current flows momentarily in the circuit including E2, Rz, C and R2, 

 By making £2 positive, and equal to or larger than Ei numerically, the plate 

 circuit of the tube becomes conducting for a short interval, the duration of 

 which is determined by the time-constant of the condenser circuit, each time 

 the contact is opened. At all other times, the plate cil-cuit is nonconducting. 

 The sharply defined electrical signal thus produced in the plate circuit can 

 be used by well-known means for direct time comparison with signals from 

 other sources. 



Making use of the duration of the impulse thus produced, it is possible to 

 use it as a selecting means to isolate a single more precise signal from a 

 continuous chain. For example, the 100-cycle wave controlled by the 

 crystal can be modified by a simple vacuum tube circuit to consist of a con- 

 tinuous sequence of very sharply defined impulses. By using the pulse 

 circuit just described as a bias control on an amplifier, it would be readily 

 possible to select one out of every hundred of these impulses and thus provide 

 an extremely precise seconds signal, the accuracy of which is determined 

 wholly by electronic means. 



It would be readily possible to vary the time relation of the seconds signal 

 while in operation, by the use of electrical phase shifters in the driving 

 circuits, or by rotating the stator of the phonic wheel motor, but for long 

 continuous operation it would be desirable to keep the number of apparatus 

 parts comprising the clock at a minimum. 



It is not necessary, of course, to employ a complete frequency divider and 

 phonic wheel apparatus for each quartz crystal oscillator. As mentioned 

 previously, the relative time rates of quartz oscillators can be measured with 

 very high precision and be very simple means through a direct comparison of 

 the high frequencies. 



Other Means for Precise Rate Control 



In addition to making improvements on the quartz crystal resonator, and 

 on methods for sustaining it in vibration, there are two other avenues of in- 

 vestigation which may yield comparable results, with possibly some addi- 

 tional advantages. Not much can be said about them at this time except to 

 point out their possibilities because no appreciable work has been done so 

 far to explore their merits as timekeepers. 



The first is in the field of very low temperatures where some quite re- 

 markable properties are obtained. Chief of these for our purpose is the 

 supraconductivity of some metals, and the constancy of shape of most 

 materials, at temperatures in the neighborhood of absolute zero. It seems 



