The Nautical Sextant

 

Forty-three years ago I paid a visit to the National Maritime Museum in Greenwich. At that time, there was an exhibition about the voyages of Captain James Cook. I looked in wonder at the fine divisions on the arc of  a sextant made by Jesse Ramsden and pondered how they might have been made. This led me to learn about engineering workshop technology and I gradually acquired some practical knowledge of dividing techniques. In the winter of 1990, in the Science Museum in London, I was able to examine a dividing engine of the type invented by Jesse Ramsden, one of the foremost instrument makers of the eighteenth century and a few days later stumbled across his prototype dividing engine in an ill-lit corner of the Musee des Arts et Metiers in Paris. After intermittently collecting and studying papers, a process much accelerated by increasing familiarity with the internet, I think I may perhaps now have something worthwhile to say about Ramsden’s circular dividing engine (he also made a linear dividing engine). I hope it will be of interest to navigators, as without dividing engines, the sextant upon which the navigator until recently relied would not have reached its final accuracy. It may also be of interest to engineers and students of the history of technology.

 It is ill-adapted to paper publication so I have offered it to readers and members of NavList. The archive of this list will perhaps last longer than I do…If you navigate to http://www.fer3.com/arc/m2.aspx?i=113701 you will find an introduction to the files and the following links to the files

 http://www.fer3.com/arc/imgx/Text.pdf

 http://www.fer3.com/arc/imgx/Commentary-on-Jesse-Ramsdens.pdf

Please leave a comment if you find these files of use or interest to you. They took a lot of effort to produce and it is helpful to know whether I should do more in the same vein.