Latitudes and Longitudes - Ciência Viva

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However, taking a clock on a boat was a tricky business. 15th , 16th , 17th and 18th century clocks did not take
kindly to the ship’s roll, the humidity and temperature differences.
From the end of the 15th century, when Columbus discovered America, to the end of the 18th century, transporting
a clock on board ship was considered the biggest problem in nautical science. Problems caused by ships sailing
off course and shipwrecks were so great that in 1598, King Philip of Spain offered a prize to anyone who could
discover a practical way to determine longitude. Later on, in 1714, the English King George III, by request of
sailors and traders, introduced the Board of Longitude Award for anyone who could come up with the solution
to the longitude problem.
An accurate time-keeping clock was designed by the English carpenter John Harrison in the mid 18th century and
its first sea test was carried out in 1736 on a voyage to Lisbon. John Harrison’s invention was only recognised in
1773, when he was awarded the Board of Longitude Award Prize.
Only after 1773 was it possible to accurately determine longitude at sea. Until then navigation was very risky with
many tales of accidents caused by sailing off course. Navigators very often played it safe and followed the same
routes along the parallels, always keeping the noon sun at the same altitude. This was the case with Christopher
Columbus who arrived in America in 1492 by sailing along the same parallel.
Sample latitude and longitude:
Lisbon: 38º 44’ N, 9º 8’ W
Oporto: 41º 8’ N, 8º 22’ W
Faro: 37º 1’ N, 9º 5’ W
Bragança: 41º 49’ N, 6º 45’ W
The Azores: 38º N, 25º W
Madeira: 33º N, 17º W
John Harrison was born in rural England in 1693 and by the time he was 18, he had already built a wooden clock. In 1730, he
left his native village for London, where he presented his sea-clock designs to Edmond Halley, one of the most famous astronomers
of the time, but Halley received the plans sceptically. In the five years that followed, Harrison dedicated himself to building the
first sea-clock prototype. This clock, which may be seen in the Greenwich Museum, still keeps accurate time. It weighed 35 kg
and had four dials which showed the day, the time, the minutes and seconds. It was tried out successfully for the first time on
the H.M.S. Centurion voyage to Lisbon where it kept time to within some seconds a day. John Harrison was about to win the
Board of Longitude Prize. Much to everyone’s surprise, he asked to be given time to perfect his prototype. Harrison was not happy
with either the precision or the size of his clock. Over the following twenty-five years, he built three more prototypes. During
this time, he had the full support of the English Royal Society and developed all of the mechanisms which form part of the working
of modern-day clocks.
The fourth clock was only finished in 1759 and it weighed 1.5 kg. After navigation tests to India, John Harrison received the
Board of Longitude Prize in 1773 and died three years later.
Today his wooden clock and his three sea-clocks are still in working order. It is forecast that the last one will start to malfunction
in four hundred years’ time!