This article is an excerpt of “Fessenden’s Underwater Ice Finder,” published in the Engineering and Technology History Wiki.
Radio communications pioneer Reginald A. Fessenden reshaped the maritime industry in 1913 through his invention of what became known as the Fessenden oscillator. Ship captains could use the electromechanical device to send underwater telegraph signals and deploy underwater echo ranging to detect icebergs and other obstacles. The oscillator proved to be the first practical form of shipboard sonar. Its underlying technology remains in use on modern vessels to measure the depth and distance of submerged objects.
The demand for such a system became evident on 15 April 1912, when the RMS Titanic sank in the Atlantic Ocean after colliding with an iceberg. That incident demonstrated that ship captains needed better technology to avoid underwater hazards and to communicate with other ships in the event of a disaster at sea.
WIRELESS TELEGRAPHY PIONEER
Fessenden was born in East Bolton, Que., Canada, in 1866, and educated at Bishop’s College, in nearby Sherbrooke. He was a math teacher before moving to the United States in 1886 to work for Thomas Edison.
For a number of years, Fessenden was a tester and researcher for emerging electrical power companies. By 1892 he moved into academic research, teaching at Purdue University, in West Lafayette, Ind., as well as the Western University of Pennsylvania (now the University of Pittsburgh). In 1900 he left academia and engaged in pioneering research in wireless telegraphy for the U.S. Weather Bureau. He designed an infrastructure for a wireless weather-station communication network.
From 1902 to 1911 he ran the National Electric Signaling Co., in Pittsburgh, where he researched radio broadcasting. The company was financially unsound, however, and in 1911 he found himself without a job.
The Submarine Signal Co. of Boston hired him in 1912 as a consulting engineer, asking him to develop a maritime echo ranging and communications system.
Fessenden’s oscillator did not generate a repetitive pulse; rather, it was similar to a microphone or loudspeaker in design. It made contact with the water through a circular metal plate. The plate was attached to a copper tube, which linked to the circular gap within a system of magnets. The magnets drew on DC and AC. They used DC winding to create a polarizing magnetic field within the circular gap. And they deployed AC winding to induce currents in the copper tube. Force was generated as the induced currents in the copper tube made a magnetic field that reacted against the polarized field in the circular gap.
That force created acoustic vibrations in the water. Ships could use the oscillator to send signals in Morse code through the water. But it was also reversible: The AC winding could be connected to a headset, allowing a listener to hear underwater sounds and echoes. Fessenden was able to detect echoes from icebergs up to 3 kilometers away, and he sometimes could hear echoes from the seabed.
Despite the oscillator’s revolutionary promise for shipboard safety and oceanography, its adoption took many years.
In a 2001 article, “Inventing Schemes and Strategies: The Making and Selling of the Fessenden Oscillator," published in the journal Technology and Culture, historian Gary L. Frost wrote that seafarers found the invention to be a godsend by making travel in iceberg-filled waters safer. Yet, for “personal, political, commercial, and institutional” reasons, the Submarine Signal Co. initially marketed the oscillator as a telegraphy system, rather than as an undersea detection device.
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