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Measuring the depth of the ocean. Reginald Fessender (1866-1932) using his invention, the electric oscillator, on a boat. This acoustic device, now known as a fathometer, was used to measure the depth of the ocean by emitting a sound and detecting its echo from the sea bed. The length of time before the echo is returned to the detectors at the sea surface indicates how deep the water is. The fathometer, which was invented in 1915, was intended for underwater signalling, communication, and obstruction avoidance device. For this pioneering invention, Fessender won the Gold Medal prize from the journal Scientific American in 1929. Photographed on 11th September 1915.
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