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Measuring the depth of the ocean. Deckhands seen with the Fessender 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 was intended for underwater signalling, communication, and obstruction avoidance device. Here, the oscillator has been successfully tested for the first time, prior to its public release as an invention in 1915. Photographed on the North Atlantic Ocean in 1914.
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