100 Greatest Science Inventions of All Time

By Kendall Haven | Go to book overview

Accurate Ship Navigation (Portable Clock and Sextant)
Year of Invention: 1759

What Is It? Two devices that, when combined, accurately determined longi-
tude (the distance east or west that a ship has sailed from its home port).

Who Invented It? Clock: John Harrison (in Lincolnshire, England). Sextant:
John Campbell (British naval officer at sea)


Why Is This Invention One of the 100 Greatest?

In 1676, the English government declared that navigation was the greatest scientific problem of the age. European countries were poised to expand into global trade and conquest. But they couldn’t do it if their ships had no way to accurately know their position when out of sight of land.


History of the Invention

What Did People Do Before?

Early sailors hugged coastlines and used landmarks for navigation. In 1100 B.C. the Phoenicians, were the first to cross the Mediterranean Sea using the Pole Star (North Star) as their navigational guide.

Navigation had improved only slightly by the late 1600s. Latitude (the distance north or south from the equator) was easy to measure with a device called a quadrant that measured the height of the sun at noon and the height of the Pole Star at night. From either of those measurements, a navigator could calculate how far north or south his ship had sailed.

However, longitude (the distance east or west of some home port) was virtually impossible to even guess. Without a way to measure longitude, a ship on the open ocean would always be lost. Shifting currents and winds might carry a ship hundreds of miles off course without the crew ever detecting it or their compass needle ever showing the problem.

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