570 BELL SYSTEM TECHNICAL JOURNAL 



tances. Sometimes the two shore stations, operating as quartz clock time 

 transmitters, must operate for hours without intersynchronization, which 

 calls for very great constancy of rate. One microsecond per hour corre- 

 sponds to one part in 3.6 X 10^. 



The precise synchronization of mechanical parts in remotely situated 

 stations can be accomplished readily. For a number of years, the 5-band 

 privacy system of the transatlantic radio telephone service has been thus 

 synchronized, the apparatus at the American terminal being controlled by 

 the Bell System Frequency Standard while that at the English terminal 

 is controlled independently by similar equipment in the British Post 

 Office. The accuracy requirement for this particular purpose is not 

 very great. However, it has been found possible to maintain two or more 

 rotating shafts at remote and independent stations so precisely controlled by 

 independent quartz oscillators that they never depart, during hours of opera- 

 tion, by more than one fifth of one degree of arc. 



A major project in which the quartz clock is destined to take an important 

 part is that of making world-wide land and water surveys in order to locate 

 more accurately boundaries and other features of the earth's surface. There 

 would be applications to sea and air navigation and it would be of great 

 value to geophysicists in studying the figure of, and changes in, the earth's 

 surface. By the combination of a widely dispersed set of Photographic 

 Zenith Tubes associated with quartz clocks and time signal means for com- 

 munication, and with the powerful ranging techniques growing out of 

 LORAN and RADAR, it should be possible to obtain a new order of ac- 

 curacy in long distance surveying. 



The new order of accuracy of time measurement has made it possible for 

 the first time to study directly the variations in longitude caused by the 

 irregular wandering of the poles. These are small effects and heretofore 

 could only be determined by inference from observations of apparent 

 latitude variations at remote stations. With the added new techniques 

 it should be possible to learn a great deal about these and other phenomena 

 related to real or apparent variations in longitude. 



Two other possible applications, involving the precise control of angular 

 movement so readily obtainable with synchronous motors operated from 

 quartz crystal controlled alternating current, are of considerable interest. 

 The first is that of operating the right ascension control of a telescope 

 directly from the amplified output of a crystal-controlled low frequency. 

 Vacuum tube amplifiers and synchronous motors are commercially available 

 with which this could be accomplished by suitable gearing. In addition, of 

 course, it would be necessary to include auxiliary controls to allow for 

 atmospheric and other transient effects, and for obtaining rates of motion 



