Figure 43. Nansen total immersion hydrometer, an instrument of variable weight
and constant volume. The fact that the instrument is completely immersed during
use explains the term "constant volume." Its principle was first put forth by
Giuseppe Pisati in 1890 and adopted by Fridthof Nansen in 1900. In 1901 it was
used by Jacob Schetelig, Nansen's assistant, from the MICHAEL SARS.