From ultrasonic to frequency standards: Walter Cady's discovery of the sharp resonance of crystals

In 1918–1919 Walter G. Cady was the first to recognize the significant electrical consequences of the fact that piezoelectric crystals resonate at very sharp, precise and stable frequencies. Cady was also the first to suggest the employment of these properties, first as frequency standards and then to control frequencies of electric circuits — an essential component in electronic technology. Cady’s discovery originated in the course of research on piezoelectric ultrasonic devices for submarine detection (sonar) during World War I. However, for the discovery Cady had to change his research programme to crystal resonance. This change followed Cady’s experimental findings and the scientific curiosity that they raised, and was helped by the termination of the war. Cady’s transition was also a move from “applied” research, aimed at improving a specific technology, to “pure” research lacking a clear practical aim. This article examines how Cady reached the discovery and his early ideas for its use. It shows that the discovery was not an instantaneous but a gradual achievement. It further suggests that disinterested “scientific” research (rather than “engineering” Communicated by J.Z. Buchwald. I am very grateful to Chris McGahey for providing me with his research notes taken from Walter Cady’s diaries kept by the Rhode Island Historical Society, henceforth Diaries. I would like to thank Aharon (Arkee) Eviatar for linguistic comments, Ido Yavetz for our helpful discussion and Jed Buchwald for his thoughtful comments and editorial work. I thank the Lemelson Center in the National Museum for American History for a grant that enabled me to study Walter Guyton Cady Papers, 1903–1974, Archives Center, National Museum of American History (henceforth, ACNMAH) and the staff of the center, especially Alison Oswald, for their help. The following abbreviations are used: NB — Cady’s research notebooks kept at ACNMAH, AIP Niels Bohr Library, American Institute of Physics, Cady’s dossier. S. Katzir (B) Cohn Institute for history and philosophy of science and ideas, Faculty of Humanities, Tel Aviv University, 69978 Tel Aviv, Israel e-mail: [email protected]