582 



BELL SYSTEM TECHNICAL JOURNAL 



pendent of the applied frequency and they expect to be able, when employing 

 frequencies corresponding to centimeter waves, to obtain a hundred or more 

 times this resolution. If this should be realized, it suggests the possibility of 

 a clock with an accuracy of better than one part in 10^. 



Perhaps the greatest advantage that might be expected from such a 

 method lies in the possible long-time stability or freedom from aging. 

 Every existing means for timekeeping involves in some manner the motion of 

 large aggregates of matter which, when they rearrange themselves in anyway, 

 vary their rates of rotation, or of oscillation, as the case may be, in ways 



20 



5 

 O 



< 



I '0 



ID 



o 



z 



o 



8 10 12 14 16 18 20 



Af IN KILOCYCLES PER SECOND 



Fig. 35 — Typical resonance curve for a line in the radio frequency spectrum of atomic 

 K^' observed by the method of molecular beams. Experimental data supplied by P. 

 Kusch and H. Taub, Columbia University Physics Department. 



that are not wholly predictable. It may well develop that a method based 

 on the behavior of single particles of matter will be ageless and, with proper 

 instrumentation, that it will permit of setting up an absolute standard of rate 

 and time interval. The actual value of this rate would be indeterminate by 

 a small amount depending on the sharpness of resonance and the precision of 

 control that could be effected from it, in addition to any uncontrollable 

 effects of the actual resonance frequencies such as result from temperature, 

 pressure, and electromagnetic and gravitational force fields. In the case of 

 some of the resonance phenomena all the latter effects are believed to be 



