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B^LL SYSTEM TECHNICAL JOURNAL 



bolic characteristic. The zero temperature coefficient makes it possible to 

 practically eliminate frequency changes caused by ambient temperature 

 changes since, by relatively simple means, it is possible to control the resona- 

 tor within db 0.01 degree C, at the temperature for which the effect is sub- 

 stantially nil. The reduction of the effect of temperature, and the stabiliza- 

 tion of the mounting, increased the stability of frequency control and oscil- 

 lator-clock rate beyond anything that had ever been obtained before. 

 Subsequent improvements that will be described later produced even greater 

 stabiUty. 



ELECTRODES 



Fig. 18 — Methods of mounting quartz ring resonators. 

 The Crystal Clock 



The striking stability of the crystal oscillator clock led the author to pro- 

 pose the general use of this type of clock for precision timekeeping, the chief 

 emphasis having been previously on the derivation of constant frequency. 

 A paper entitled "The Crystal Clock,"^® presented before the National 

 Academy of Sciences in April, 1930, described such a clock and pointed out 

 some of its properties and likely uses. 



Chief among these properties, of course, is its inherent stabiHty and rela- 

 tive freedom from extraneous effects. The quartz crystal clock is not 

 dependent on gravity and, without any compensating adjustment, will 

 operate at the same rate in any latitude and at any altitude. This property 

 already has been useful in the measurement of gravity and gravity gradient 

 by measuring the rates of pendulums on land and at sea.^"- ^^ 



The crystal clock is practically immune to variations in level and shock 

 and can be used as an instrument of precision under conditions entirely 

 unsuitable to pendulum clocks. For this reason it performs satisfactorily 

 in practically any location, including earthquake zones, and may be used in 

 transit as in a submarine, in an kirplane or on the railroad. 



