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Plate 2. Magnifying glass devised by Fridtjof Nansen for reading thermometerscales. The thermometer is placed such that the two notches designated c areon the thermometer; the thermometer is adjusted such that the top of the mercury column is located at point d; and the reading glass is focused for readingthe thermometer by turning the interior tube a within tube b. (Image credit: Oceanographic Museum of Monaco)