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![Figure 45 ship4419.jpg Figure 45](/sites/default/files/styles/max_1300x1300/https/s3.amazonaws.com/s3-east-testmedia-noaa.woc.noaa.gov/dam/Photos/legacy/pl23_ship4419.jpg?itok=moViQ48c)
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Figure 45. Pettersson small chain hydrometer, designed by Professors Otto andHans Pettersson in 1917. This instrument eliminated difficulties associatedwith the surface tension of the sample as well as variations of volume. A small metal chain helped achieve a balance by compensating for the buoyancy of thefloat as a function of the density of the liquid. (Image credit: Oceanographic Museum of Monaco | Y. Berard)