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Figure 42. Hopfgartner and Arzberger sounder, devised by Lieutenant Franz vonHopfgartner of the Austrian Merchant Marine and Moriz Arzberger, a civil engineer, this apparatus used the same principle as aneroid barometers which utilizedthe pressure difference between a wall, isolated or not, and the exterior medium. It was tested in 1876 in the Gulf of Trieste in depths up to 17 meters. (Image credit: Oceanographic Museum of Monaco | Y. Berard)