One of the earliest diagrams of echo-sounding in a published work. Source: In Die Meteor-Fahrt Forschungen, The Meteor Expedition (1928) by F. Speiss.
Citation: In Die Meteor-Fahrt Forschungen, The Meteor Expedition (1928) by F. Speiss. Fahrt Forschungen und Erlebnisse der Deutschen Atlantischen Expedition, 1925-1927. D. Reimer, Berlin. (NOAA Photo Library.)
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