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    Re: Accuracy: main shades vs eyepiece shades?
    From: Brad Morris
    Date: 2019 Jul 27, 15:08 -0400
    thanks Geoffrey.  

    On Sat, Jul 27, 2019, 3:00 PM Geoffrey Kolbe <NoReply_GeoffreyKolbe@fer3.com> wrote:

    Brad Morris said:

    "I selected ~ 1900  as a date by which nearly all sextants were made using float glass.  Its probably earlier."

    "Float glass" - where glass solidifies on the surface of a bath of molten tin, and so is optically flat top and bottom without further polishing - was developed by Pilkington Brothers in the mid 1950s. 

    Geoffrey Kolbe

       
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