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Re: Testing sextants in 1885
From: Henry Halboth
Date: 2009 Jul 15, 20:38 -0700
From: Henry Halboth
Date: 2009 Jul 15, 20:38 -0700
Frank, Your quotation from Bro. Clarke's 1885 work, which is quite familiar to me, includes the statement, with reference to centering error (arc) error ..... "The error being found for certain places on the arc, the correction for any angle may by proportion be obtained." In my opinion, for what it may be worth, this statement is not technically correct. Arc error, which necessarily includes centering error, graduation errors, deformation error, and the residuals of any other uncorrected errors of mirror parallelism and perpendicularity, as well as telescope collimation and mirror prismatic errors does not necessarily change proportionately over the full extent of the arc and should be individually determined at any measured angle - or at least at far lesser intervals than is normally done. This error may also change over the years and old certificates certainly should not be taken as Gospel. Clarke's little book is great, but there are others out there, including "The Sextant and its Applications", Simms 1858, which go into the subject far more exhaustively, and may well appeal to the more technically minded. Regards, Henry --- On Wed, 7/15/09, frankreed@HistoricalAtlas.com <frankreed@HistoricalAtlas.com> wrote:
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