The clock that found the sea: warm-up · Grade 10

The passage and its 4 questions

Directions: Read the passage carefully. Then answer the questions in full sentences.

• For most of history, sailors far from land could answer only half of the question "Where are we?" Latitude, a ship's position north or south, could be worked out from the height of the sun at noon or of certain stars at night. Longitude, its position east or west, was another matter. Without it, navigators guessed, and a wrong guess on a dark coast could be fatal. In 1707, navigation errors helped wreck four British warships off the
• Isles of Scilly, and well over a thousand sailors drowned.
• The science of the problem was simple. Earth turns 360 degrees in 24 hours, or 15 degrees every hour. If a navigator knew the time at the home port and the local time on board, the difference between them would reveal how far east or west the ship had traveled. Local time was easy: noon is when the sun stands highest. The hard part was carrying home-port time across an ocean. The pendulum clocks of the age could not keep steady time on a rolling deck, in damp air, through heat and cold.
• In 1714, the British Parliament offered a reward of up to 20,000 pounds, a fortune at the time, for a practical method of finding longitude at sea. Many leading astronomers backed a method based on careful measurements of the moon against the stars. An unlikely rival appeared: John Harrison, a carpenter from the north of England with little formal schooling, who believed the answer was simply a better clock.
• Harrison spent decades on the problem. His first three sea clocks were heavy brass machines full of ingenious devices to resist motion and changes in temperature. His fourth design, finished in 1759, was a surprise: a large pocket watch only about five inches across. On a voyage to Jamaica in 1761 and 1762, it is reported to have lost only about five seconds.
• Success did not bring an easy reward. The Board of Longitude, which included astronomers committed to the lunar method, demanded further trials and questioned his results. Only in 1773, after the aging Harrison appealed to King George III, did
• Parliament grant him a large payment. By then, a copy of his watch had sailed with
• Captain James Cook, who praised it highly. Harrison died in 1776, and within decades marine chronometers became standard equipment at sea.
• The story is often told as a lone genius defeating stubborn experts, but it is more tangled than that. The lunar method also worked, and navigators used both for years.
• What Harrison proved was that a problem of the heavens could be solved by craft as well as by theory.
• 1. What problem does the passage describe, and how did Harrison's approach differ from the astronomers'?
• 2. Why might the astronomers on the Board of Longitude have been slow to accept
• Harrison's results?
• 3. In paragraph 3, Harrison is called 'an unlikely rival.' What does 'unlikely' suggest, and why is it apt?
• 4. Evaluate the strongest and weakest evidence in the passage.