Invention of a Chronometer – a Big Progress in Sea Navigation

old nautical map of atlantic

Nautical Map of the Atlantic Ocean by the Coast of Spain, Portugal, Gibraltar and Morocco, 1760

This is a nice example of what are known as portolan charts – navigational maps based on compass directions and estimated distances observed by captains at sea. Portolan maps have one main compass rose in the middle with 16 other compass roses located in a circle around the main rose.

The Age of Discovery peaked with James Cook and his famous voyages in the second half of the 18th century. The biggest problem in sea navigation was solved around this time when the marine chronometer invented by John Harrison enabled the measurement of accurate time and, therefore, accurate longitude at sea. Whereas latitude could be easily determined at sea by measuring the sun’s angle at noon, the measurement of longitude remained a major problem until the 1760s. With the invention of the chronometer, it was possible to accurately measure the time of a known fixed location, for example, Greenwich Mean Time (GMT). Knowing GMT at local noon allows a navigator to use the time difference between the ship’s position and the Greenwich Meridian to determine the ship’s longitude.

The Royal Greenwich Observatory displays a collection of the first chronometers invented by John Harrison. His life-story is narrated by Kathryn Lasky in her children’s book “The man who made time travel”.

Buy restored reproduction of this map printed on a high quality handmade paper here.

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