Fill in the Blanks (Reading & Writing)

Choose the word that best fits each blank.

For centuries, sailors navigating the open ocean faced a stubborn problem: while they could measure their latitude fairly easily by observing the sun or stars, calculating their longitude remained dangerously unreliable. The key, scientists eventually realised, was accurate timekeeping. Because the Earth rotates a fixed amount each hour, knowing the precise time at a fixed reference point and comparing it with local time aboard ship would reveal how far east or west a vessel had travelled. The trouble was that ordinary clocks lost accuracy at sea, thrown off by the rolling of the ship and changes in temperature and humidity. In the eighteenth century, a self-taught English carpenter named John Harrison devoted decades to building a clock robust enough to keep reliable time during long voyages, finally solving a puzzle that had defeated the leading astronomers of his age.

Sailors could find their latitude easily, but determining —longitudelatitudedepth was unreliable until scientists realised the answer lay in accurate —timekeepingmapmakingstargazing; ordinary clocks failed at sea, so John Harrison spent decades building one robust enough to —keeplosewaste reliable time during long voyages.