Figure 42. Hopfgartner and Arzberger sounder, devised by Lieutenant Franz von
Hopfgartner of the Austrian Merchant Marine and Moriz Arzberger, a civil enginee
r, this apparatus used the same principle as aneroid barometers which utilized
the 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.