Stigma

The position of any place on the earth’s surface is determined by its latitude and longitude. Throughout the centuries, it was relatively easy for seamen to guess the latitude of their position by the length of day time in relation to the season and by the angle between the direction of stars and the horizon (altitude) that they determined by eye or with instruments.

However, finding the longitude, that is at what distance west or east they were, was a great problem for many centuries until it was finally solved in the 18th century.

Portrait of John Harrison (1693-1776)

The prize winning chronometer of John Harrison.

In July 1714, the English parliament passed an act (The Longitude Act) that offered a prize for the solution of the problem. It was won after many years by an English clockmaker, John Harrison, who made the first nautical clock (chronometer) that kept precise Greenwich mean time no matter what the conditions of the journey. Later, an English man, John Hadley, and an American, Thomas Godfrey, presented almost at the same time an instrument called an octant to determine the angular distance of the sun from the moon during the day and the moon from the stars at night. With the help of tables that gave this angular distance for each hour of the day and each day of the year, the longitude and latitude could be found.
An improved version of the octant is the modern sextant that measures angles up to 1200 and has an arc of 600 (1/6 of a circle) with subdivisions.

Chronometers of Galaxidi captains