Sextant Studies

A quick note: my name is Mike Romero, and I'm a Historic Interpreter at Colonial Williamsburg.  The postings I make on this site are my own personal opinions and research, and do not necessarily reflect the views of Colonial Williamsburg.  With that said, enjoy the read!

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I've been silent here for a few months, due primarily to being bogged down in research and training opportunities at Colonial Williamsburg.  A lot is happening at my end, and I've been trying to make the most of it.  Nonetheless, it's high time for a new post.  I thought I'd center my first post of the new year around one of my favorite props/instruments: the sextant.

For those not familiar with the story, early in the summer of 2016, I came across an excellent article on British Tars called "The Tools Needed for Dead Reckoning."  It described instruments like the chip log, log board, etc. and how they were used by mariners to approximate their use at sea.  As I'd recently been given a fair bit of leeway to interpret an 18th century sailor at Colonial Williamsburg, I thought this an excellent opportunity to develop an activity and demonstrate a purely nautical still at work that you wouldn't be likely to see anywhere in town.  Armed with an early 1700's map of the Caribbean, an improvised chip log, log board, and protractor, I set to work.  Setting up on a stack of crates along Duke of Gloucester, guests were quickly drawn to the map and began asking about what I was doing.  On numerous occasions throughout each day, I'd have small groups working with me to use the tools to plot an imagined course along the sea.  Very pleased to be having a positive impact with my dead reckoning demonstration, I described my successes on Facebook.  Not long after, I came home from work to find a package from Amazon from an unknown sender.  I opened it up to find the object in the picture, a nautical sextant stamped with "J. Scott, London 1753."

Obviously, I was surprised.  I'm still not sure who was kind enough to send this to me (I suspect it was a member of my family who is enthusiastic about what I had been doing), but I soon put the sextant to good use.  I was able to learn how to use the sextant fairly quickly by watching videos like this one on YouTube, and thanks to the Navigation in the Age of Sail group on Facebook, I was able to find a copy of the Nautical Almanac and Astronomical Ephemeris for the Year 1767 via Google Books.  From there, it was relatively easy to begin interpreting a noon sighting and showing guests how the sextant could be used to determine one's latitude.

Predictably, after going through the activity and seeing the sextant at work, guests frequently asked me, "Is this a real sextant from the time period?" Finding a complete answer to that one took some doing, but eventually I was successful.  Searching the maker's stamp on my sextant didn't yield me much...it doesn't seem to be based in any history I can find (yet), and searching "J. Scott London" online only takes you a page where you can purchase the sextant itself.  Multiple online sources, however, state that the first sextant was not produced until 1759 by John Bird.  Most images or descriptions of sextants I found from the period were made primarily of woods like mahogany or ebony, and numerous sources suggesting brass sextants were much heavier for their size and provided an undue amount of wind resistance when being used at sea.  Undaunted, I looked for more information on period sextants.  In reading through the 1767 Nautical Almanac to try and teach myself the lunar method for finding longitude (an uphill battle and one that frequently produces migraines, I assure you), I came across this description of an ideal instrument to be used:

"But it will be more convenient if the Instrument be made a Sextant, in which case it will measure 120o for the Sake of observing the Moon's Distance from the Sun for Two or Three Days after the first and before the last Quarter.  The Instrument will still be more fit for the Purpose, if it is be furnished with a Screw to move the Index gradually in measuring the Moon's Distance from the Sun or Star; an additional dark Glass, lighter than the mommon ones, to take off the Glare of the Moon's Light in observing her Distance from a fixed Star, and a small Telescope magnifying Three or FOur Times to render the Contact of the Star with the Moon's Limb more discernable.  A magnifying Glass of 11/2 or Two Inches Focus will assist the Observer to read off his Observation with greater Ease and Certainty."

Brass notwithstanding, this describes my own sextant fairly well.  It's tough to see in the image I posted at the top of the page, but my sextant does have a small telescope to magnify the image in the horizon mirror, a short focus magnifying glass to better read the index, and light and dark shades for the lenses.  More recently, I came across this tidbit in A Voyage Towards the North Pole, published in 1774 by Constantine Phipps of the Royal Navy as a chronicle of his expedition the previous year:

"The observations for finding the time at sea, were taken with a brass Hadley's Sextant of eighteen inches radius, made by Dollond; and sometimes by Captain Phipps, with a smaller of four inches radius, made by Ramsden, which commonly agreed with the other within a minute."
(From an appendix to the journal entitled Account of the Astronomical Observations and Time-Keepers, by Mr. Lyons.")

So while it may not be an exact replica of any particular piece, I'm able to conclude that sextants with the same features as mine may have been highly desired by readers of the 1767 Almanac, and that a sextant of similar size and material to mine (my own is only about four inches in radius) was in use in 1773.  With this information, I can show the guests a decent representation of a navigational instrument that could have been available to navigators of the late 18th century, and they boggle at how accurate these instruments could prove.  (Earlier this month, I calculated the south gate of CW's Capitol Building to within 2.4 nautical miles using my sextant and chronometer.)  As a visual curiosity, the sextant has drawn attention of guests from all ages from children interested in tools and science of the time to a World War II veteran (likely my most rewarding interpretive moment to date) who used a sextant while serving as a navigator aboard a B-17.

Keep in mind friends, I'm only at the tip of the iceberg when it comes to octants, sextants, and other navigational instruments of the 18th century.  I know full well there is a lot more to learn on the subject, and I look forward to the experience.

Sources:
British Tars, The Tools Needed for Dead Reckoning: http://britishtars.blogspot.com/2016/06/navigators-week-tools-needed-for-dead.html
Google Books: The Nautical Almanac and Astronomical Ephemeris for the Year 1767
YouTube: Getting Started in Celestial Navigation - The Marine Sextant
The History of the Sextant: http://www.mat.uc.pt/~helios/Mestre/Novemb00/H61iflan.htm
Google Books: A Voyage Towards the North Pole