Sextants

Sextants in Nautical History

We may marvel at today’s GPS system which allows sailors to pinpoint their location with great accuracy, but perhaps even more remarkable is the instrument which has been helping sailors do this since the early 18th century, the sextant. As most sailors know, if there are no visible landmarks to help you locate your position, the sextant can give you that information by allowing you to first calculate the position of celestial objects, such as the Sun, in relation to your own position and the horizon. Through reflected mirrors, sextants cleverly allow an observer to line up the Sun with the horizon thus calculating an angle which can then be used in conjunction with navigational tables and the time to calculate the position of the observer.

It was Sir Isaac Newton who first had the idea back in the late 17th century of how a doubly reflecting navigational instrument could work in principle. It was John Campbell, however, a British naval officer, who actually invented the sextant in 1757, the name sextant deriving from it having an arc of 60°, one-sixth of a full circle. Before then, sailors had used the octant, its predecessor, which was invented independently by English mathematician Thomas Godfrey and American inventor John Hadley. The great advantage of the sextant over the octant was that it could measure latitude and longitude whereas the octant could only measure latitude. Sextants also replaced other instruments such as a backstaff (generally an instrument which measures the altitude of the Sun by measuring the projection of its shadow) and much earlier navigational instruments such as the cross-staff and the mariner’s astrolabe.

Since its invention, the sextant has played an integral part in world history. In navigation and exploration, it has been crucial to the landmark voyages of such illustrious names as Captain James Cook, Robert FitzRoy of the Beagle and Sir Francis Chichester. In itself, a sextant is a beautiful instrument in design and engineering. Today, if, for any reason, such as a technological breakdown, GPS can’t be used, the sextant can still be a lifesaver as it has been throughout the centuries. It’s partly for this reason that sextants are still widely carried and used today by sailors and navies across the world.

Photo Credit: El Bibliomata via Compfight cc

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