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Navigation history - Sextants

by Joan Wenner 17 Feb 19:36 UTC
Sextant US Geological Survey Quintant Sextant © Joan Wenner

Sextants and Mapping the Oceans

John Bird is said to have made in London one of the very first sextants around 1758. Quite large, it is also unusual in having a pole that fits into a socket on the observer's belt to help support the instrument's weight.

(Nevil Maskelyne the London astronomer born in 1732,and Royal Society member, is recognized too for his contribution to the science of navigation.) The doubly reflecting navigation instrument measuring the angular distance between two visible objects, shaped in the form of a sector - 60 degrees or 1/6 of a circle, i.e. sixth (Latin word for sextans) part of a circle.

Open Ocean Challenges

In the fine book Sextant by David Barrie (the great-great-nephew of writer J.M. Barrie),he writes, "For two hundred years mastery of the sextant was a vital qualification for every ocean-going navigator. "He observes that even as late as the early twentieth century basically the only way to navigate a smaller sailing vessel across an ocean was with a sextant to measure the height of the sun and stars above the horizon, along with a chronometer to determine the exact time of each sight.

Also described are the challenges of celestial navigation,including measuring a sextant angle with complete accuracy and recording the exact time of a sight.Explained is that much of the mechanics of this form of navigation,including the modern intercept method done without the need to draw big circles,as demonstrated by Marcq St.Hilaire in the last century.

The precision marine tool comes in sizes ranging from pocket-sized to grand heavyweights perfectly adapted for use. Just a few hundred years ago it was impossible to determine longitude on board ship with any accuracy. Thus in 1714 an act of Parliament was passed designed to encourage the development of a practical shipboard solution to the age-old problem and within 50 years and the space of a single decade, two methods, one mechanical the other astronomical, were introduced, both depending on the new instrument: the sextant.

Captain Bligh and his sextant

The mutiny aboard the Bounty is of course familiar history. Much is learned through entries William Bligh wrote in logs {see Sidebar] after set adrift in 1789 in a longboat with some crew while returning to England from Tahiti where engaged in ferrying bread fruit. He was a captain in the Royal Navy with a reputation that would dog him the rest of his life of having a volatile temper often clashing with his fellow officers and crewmen. While not permitted to take a chronometer, he was however an experienced and expert navigator utilizing the means he had available.

Sextant William Bligh Sidebar log entries and history

The famous or infamous Captain William Bligh (and exceptional navigator)story is well known. Set adrift in April of 1789 from the sailing ship Bounty in a 7.01 metre (23 feet)longboat with 18 still loyal sailors he was allowed a compass and a sextant. Even as gales blew, he was still taking sights of the sun and stars, along with writing notes of islands they passed.

Terrifying and sometimes fascinating travails in their quest to stay alive were captured in logs he kept. For example, "At dawn of day I found everyone in a most distressing condition, and I began to fear that another night would put an end to the lives of several, who seemed no longer to support their sufferings."

However due to Bligh's skills, including with the brass navigational instrument first invented around 1758 used to determine latitude, they reached a habitable island with no loss of life and feasted on oysters and berries, gaining hope they would survive. In another log entry Bligh's boatswain observing his captain wrote, "He innocently told me that he thought I looked worse than anyone in the boat. The simplicity with which he uttered such an opinion amused me and I returned him a better compliment."

Early history

He first went to sea at age 7 as a captain's personal assistant on the HMS Monmouth, and officially joined the Royal Navy in 1770 and in 1787 at age 33 was given command of the three-year old Bounty which sailed from Britain on December 23,1787 bound for Tahiti with the mission being to ferry bread fruit to the West Indies.

It's noted in historical archives that he was an intelligent man, well-versed in science and mathematics. He would become at age 22 Sailing Master aboard the Resolution (commanded by Capt. James Cook who would die on this voyage in 1779). During a 12-month leave from active duty, Bligh met his future wife, the daughter of the Collector of Customs. Already a Lieutenant he had made several important hydrographic surveys. Shortly after the marriage it was back to sea duty where he saw action in the battles of Dogger Bank in1781 and fought with Lord Howe at Gibralter in 1782.

In 1787 he was given command of the three-year old Bounty with it's said with mostly a crew of illiterate recruited men for this voyage where Bligh would become one of their victims.

More to the story

Upon his return to England in November of 1790 and where his navy career resumed, he was placed in charge of several more commands of ships that included captaining the HMS Falcon, a year later the HMS Providence and a succession of vessels thereafter to 1805 when he was sent to serve a troubled 3-year stint as Governor of New South Wales resulting in being forcibly removed.. Back in England yet again he was promoted to the rank of Commodore (1808), Rear Admiral of the Blue (1810), and lastly Vice Admiral of the Blue (1817).

In later years he lived in Kent and died in 1817 at Broad Street, London at the age of 64. He is buried in the eastern part of Lambeth Churchyard next to his wife by whom he had six daughters.

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