a
reference to a
Fathometer, a
trademark for a device
developed in the early 1900s which is used on ships to
measure the depth of the water beneath the
hull to avoid shallow areas or detect underwater objects. It works by sending a
sound from the bottom of the
ship to the ocean
floor and measuring the
time it takes for the
sound's echo to
return to the
ship. Knowing how long it takes for
sound to travel in water, one can calculate how deep the bottom is.
Kelvin refers to Irish
physicist Lord Kelvin (1824-1907) who invented an earlier device for detecting a water's depth, in 1872, consisting of a weighted
wire attached to a drum on the deck of a
ship.
Fathometer comes from fathom, a measurement of depth, and
meter, an
instrument for measuring.