542 BELL SYSTEM TECHNICAL JOURNAL 



constructed with a sort of narrow shelf at the central plane that could be 

 mounted in a horizontal plane on pin supports. The two methods of sup- 

 porting the ring resonators are illustrated in Fig. 18. Such resonators were 



Fig. 13 — Set of rectangular quartz resonators made for zero temperature coefficient study. 



Fig. 14 — Circular pieces remaining after temperature coefficient study of quartz discs 

 and rings. 



Fig. 15 — Large crystal and slab from which low coefficient studies were made. 



used in the Bell System Frequency Standard until 1937 when they were 

 replaced by an entirely different type that will be described later. 



The rings were adjusted to oscillate at 1(X),000 vibrations per second, 

 the frequency which has been adopted in nearly all oscillators of extremely 



