SOUNDING WEIGHTS
Today,
a relatively inexpensive G.P.S. receiver can indicate the position of a
ship within a few meters, and moving charts on a video screen
facilitate navigation. Until relatively recently, however, the compass
was not particularly accurate, and navigators were dependant on charts
of widely varying accuracy. Since the depth of water beneath a hull is
always a primary concern, the sounding-weight—known in the Mediterranean
by at least the sixth century B.C.—remained a critical navigational aid
on seas and rivers well into the twentieth century.
A sounding-weight is a roughly bell-shaped mass—usually made of lead—averaging about five kilogrammes in weight, with a sturdy attachment lug at its apex and a tallow cup in its spreading base. Ancient mariners used sounding-weights, the oldest known marine navigational instrument, not only to determine the depth of water, but also to bring up samples of the bottom, comparing the result with their knowledge of coastal geography and river behavior.
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