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![Figure 38 ship4043.jpg Figure 38](/sites/default/files/styles/max_1300x1300/https/s3.amazonaws.com/s3-east-testmedia-noaa.woc.noaa.gov/dam/Photos/legacy/pl23_ship4043.jpg?itok=KmmzfVPH)
Description
Figure 38. Percussion current meter invented by Julien Thoulet. Top: Number99 0610. Bottom: Number 99 0611. When the helix turned it caused a striker to fall on a steel plate. The sound of this was recorded by a hydrophone and thenumber of recorded sounds per unit time was directly related to current strength. This was tested off Monaco by Dr. Jules Richard in 1921. (Image credit: Oceanographic Museum of Monaco | P. Roggero)