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 reco
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Photographer: P. Roggero
Credit: Oceanographic Museum of Monaco
Subject: Oceanography
Subject: Historical instruments