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    Re: Anyone seen one of these before?
    From: Stephen N.G. Davies
    Date: 2015 Apr 5, 21:14 +0800
    Yes, I bought something similar by Troughton for the Hong Kong Maritime Museum about 6 years ago and it is on display in their gallery 10. Troughton was convinced (I suspect not having entirely internalized the revolutionary implications of Ramsden's dividing engine) that having three readings around a circle and averaging the result was more accurate than a single reading on just one arc. There is a good exposition in the late 19th century Penny Cyclopedia. The idea didn't catch on. Circular 'sextants' are often confused with repeating circles.

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    On 5 Apr, 2015, at 9:06 pm, David Pike <NoReply_DavidPike@fer3.com> wrote:

    Whilst searching for Plath arcs on Google images, I came up with the attached instrument by Henry Hughes. http://www.liveauctioneers.com/item/35521567_a-rare-victorian-5-12-brass-double-sextant-by-henry It looks like something from "Around the world in 80 days".  Has anyone seen one before? What was it used for, and how was it used? It's interesting to see the cabinet makers cutting guage marks on the dovetails in the the box.  Was this a sign of piecework or of a a true craftsman?? Dave

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