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Barrow on Humber castle remains. Photo:
David Wright
CCL
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These earthworks are all that remain of the Norman motte & bailey castle at
Barrow-upon-Humber but they are nevertheless impressive (Map ref: TA 065 225).
Famous son of this town is
John Harrison 1693-1776, the inventor of the
first marine chronometer - a clock designed to
keep accurate time whilst at sea, essential
for calculating a ship's longitude.
Although John was born
near Wakefield, the family moved to
Barrow-upon-Humber soon afterwards and it was
here that he grew up.
He trained in his father's
joiners shop but he developed an interest in
clock-making. After almost 300 years, one of
his is still in good working order at nearby
Brocklesby.
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John Harrison |
As trans-oceanic journeys became more frequent, a system was needed to plot a
ship's accurate position on a chart. In October 1707 in thick fog, part of the
English fleet under the command of Sir Cloudesley Shovell ran aground in the
Scilly Isles even though their navigation calculations had indicated they were
in safe waters. Over 2000 men died in that incident and the Government
established a prize of up to £20,000 for anyone who could find a method of
calculating longitude at sea.
To accurately know their ship's position, a crew needed to be able to calculate
its latitude and its longitude. The former could be obtained by measuring the
elevation of the Pole Star but longitude was not so easy to calculate using
astronomy. Harrison's method was to create a clock that could keep accurate time
of the home port. Using sun sights, the crew could calculate "local" time at sea
and, by comparing with the clock, they could find the difference in time and
work out their longitude.
The earth rotates 360 degrees in 24 hours (1440) minutes. Therefore every 4
minutes, the earth rotates 1 degree of longitude. If a ship were 1 hour behind
the time at their home port, they knew that they were 15 degrees west of their
starting point. Political wranglings stopped him winning the actual prize but he
was eventually paid an equivalent sum by parliamentary decree. |
