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BELL SYSTEM TECHNICAL JOURNAL 



is also sent out into the ocean. It strikes the bottom and is reflected back 

 causing another mark to appear on the record. Knowing the difference in 

 time and the velocity of sound in sea water, the distance to the bottom can 

 be measured. A typical record is shown in Fig. 1.2. The top record shows 

 the contour of the sea bottom while the second record shows the reflections 

 from a school of fish. 



At about the same time, Nicolson at Bell Telephone Laboratories was 

 experimenting with Rochelle salt, another piezoelectric material having a 



Fig. 1.1 — Ultrasonic transmitting apparatus 



much larger piezoelectric effect than quartz. He constructed and demon- 

 strated loud speakers, microphones, and phonograph pick-ups using Rochelle 

 salt.^ He was also the first one to control an oscillator by means of a crystal 

 — in this case Rochelle salt — and has the primary crystal oscillator patent.- 

 Nicolson's circuit is shown in Fig. 1.3. The crystal is effectively in a path 

 between the resonating coil in the output and the grid, since the electrode 



^ "The Piezoelectric Effect in the Composite Rochelle Salt Crj'stal"- 

 Froc.A.LE.E. 1919,38, 1315. 



2 See Patent 2,212,845 filed April 10, 1918; issued Aug. 27, 1940. 



-A. M. Nicolson, 



