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The Dawn of Ultrasonics
cally active as a notable anti-fascist, which resulted in house arrest by the Vichy government for most of World War II.
By comparison, Boyle had come across the pond in 1909, following his PhD mentor Rutherford. Boyle was born in Newfoundland and educated in Montreal at McGill Univer- sity, receiving the first PhD in physics from McGill University studying radioactivity. Boyle returned to Canada in 1912 to start the physics program at the University of Alberta (Edmonton, AB, Canada) where he shifted to the new field of ultrasonics. With the advent of World War I, Boyle volun- teered and joined the BBIR back in England. In 1919, Boyle returned to Alberta where he became dean of applied sci- ence and was elected two years later to the Royal Society of Canada. Boyle was a major contributor to the development of Canadian science as director of physics for 20 years at the National Research Council.
The Prankster of Baltimore: Robert Williams Wood
Among those to whom Langevin displayed his work at Toulon was Robert W. Wood, professor of physics at Johns Hopkins University (Baltimore, MD; Figure 3). Wood had been asked to assist the US armed services shortly after the entry of the United States into World War I. He participated in antisub- marine projects and was present at a June 1917 meeting in Washington with the French-British delegation where Langevin’s work was reported.
Wood had previously contributed importantly to the early concepts of acoustics and shock waves. Visualization of acoustic phenomena was limited in 1900, so to better illus- trate the wave properties of sound, Wood photographed (using spatial differences in refractive index) the actual wave fronts of sound waves and demonstrated vividly all the phenomena of reflected and refracted waves. These photo- graphs received wide attention, brought Wood international acclaim, and resulted in an invitation to lecture before the Royal Society.
Commissioned as major in the army, Wood gained permis- sion to devote particular attention to Langevin’s work. As he later wrote (Wood, 1939, p. 35), “It was my good for- tune during the war to be associated for a brief time with Prof. Langevin during his remarkable developments. At the arsenal at Toulon I witnessed many of the experiments with the high power generators...the narrow beam of supersonic
Figure 3. Robert W. Wood (1868–1955) posing in front of a spinning mercury telescope mirror that he built in the barn of his Long Island summer home. Photo taken in ~1915. Photo courtesy of the American Institute of Physics (AIP) Emilio Segre Visual Archive.
waves shot across the tank causing the formation of millions of minute air bubbles and killing small fish which occasion- ally swam into the beam. If the hand was held in the water near the plate an almost insupportable pain was felt, which gave one the impression that the bones were being heated.”
This observation of Langevin’s work lay dormant in Wood’s mind for a decade but reemerged during his interactions later
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