Figure 11. Buchanan mercury piezometer (VORINGEN model) - This piezometer
was designed by Henrik Mohn who was inspired by Buchanan's earlier CHALLENGER
design. Mohn had this instrument fabricated by Louis Casella and used it to
determine depths of observation of Negretti and Zambra reversing thermometers
used during the Norwegian VORINGEN expedition in 1877-1878.
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