Ships' captains of the 17th century made long oceanic voyages calculating their latitude distance from the equator - by (0) observing the night sky, but not knowing their longitude (distance from the prime meridian). An accurate clock keeping an exact record of the time at a ship's starting point was needed to determine this.
However, contemporary clocks worked inaccurately in the poor conditions aboard sailing ships. The British parliament offered a reward of £20,000 to whoever (26)
invent a timepiece able to cope with the wide (27)
in temperature, pressure and humidity and so work reliably. The person who accepted the (28)
was John Harrison, a carpenter and clockmaker.
Having already (29)
clocks with moving parts made from wood, he adapted his ideas firstly into a series of marine clocks, and some time (30)
watches, that became famous worldwide. Sadly, he never received the full amount of the prize, even though his clocks can be seen - still working - in London museums today. A self-educated provincial tradesman, he made powerful enemies in the Royal Society, who always underestimated his achievements.
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