EVOLUTION OF QUARTZ CRYSTAL CLOCK 565 



comparable information which, of course, by nature, could never reveal 

 short-term factors. 



Soon after the inauguration of the quartz clocks at the Physikalisch- 

 Technische Reichsanstalt, somewhat similar installations were made at the 

 Prussian Geodetic Institute at Potsdam^^^, and at the Deutsche Seewarte in 

 Hamburg"^ The latter has been moved because of war conditions and is now 

 the Deutsche Hydrographische Institut. The quartz resonators used in these 

 installations are believed to be similar to those in Clocks III and IV in the 

 Physikalisch-Technische Reichsanstalt installation except that some of them 

 were made for 100 kilocycles instead of the original 60 kilocycles. They 

 were made by the firm Rohde and Schwarz where also is maintained a quartz 

 clock installation of extremely high precision "^ 



For a number of years the U. S. Bureau of Standards at Washington, D. C. 

 has maintained a quartz clock installation for their extensive constant 

 frequency and time services. The early history of this installation was 

 described in some detail by E. L. Hall, V. E. Heaton and E. G. Clapham in 

 1935.^^- As is now well known, the Bureau broadcasts a number of precisely 

 controlled carrier frequencies at all times, all of which carry standard time 

 and frequency modulations, including audible pitch standards and time 

 signals. The audible pitch standards are 4000 cycles and 440 cycles, while 

 the time signals consist of a succession of seconds pulses, continuous except 

 for certain omissions for the purpose of identifying longer time intervals. 

 All of these rates, including the carrier frequencies, are derived directly from 

 crystal oscillators and are known so well that their accuracy as transmitted 

 is estimated as one part in 50,000,000 at all times. The relative rates of the 

 standard oscillators are compared and recorded continuously at the Bureau 

 of Standards with an accuracy of one part in 10^. The time signals involved 

 in these transmissions are so precise, and so convenient to use, that they 

 may be employed for the high-precision intercomparison of quartz clocks 

 across the Atlantic and for studies in astronomical time, heretofore difficult 

 or impossible to accomplish by any other means. 



The present standard frequency and time service facilities at the U. S. 

 Bureau of Standards, which have been instituted under the general direction 

 of J. H. Dellinger, are described in recent separate articles ' by Vincent 

 E. Heaton and W. D. George respectively of the Bureau, both of whom have 

 made very substantial contributions to this development. The transmitting 

 station for the standard frequency broadcasts, which comprises a complete 

 set of quartz oscillators and control and measuring equipment, is shown in 

 Fig. 32. 



The absolute rates for the crystal oscillators at the Bureau of Standards 

 are determined through cooperation with the U. S. Naval Observatory, also 



