NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Coordinates on Cook's maps
From: Alexandre Eremenko
Date: 2007 Apr 20, 08:04 -0400
From: Alexandre Eremenko
Date: 2007 Apr 20, 08:04 -0400
Dear George, I am impressed with your list of error in Moscowitz papers. You would be an ideal referee for a scientific journal; did any of the two Navigation journals ever use your service? (I would be delighted if all my papers were refereed so carefully:-) Yesterday I re-read Moskowitz's paper on the first sextants, and found that it actually contains some relevant info to our recent discussion of the circle division. According to Moscowitz, Bird claimed 0.001 (one over thousand) of an inch accuracy in his manual circle division. Thus he divided large sextants to 1' and smaller sextants to few minutes. Moscowitz carefully studied the arcs of surviving sextants but apparently made no attempts to verify Bird's accuracy claims. Now when the first dividing engine was invented, a sextant was divided on this engine, "in the presence of Longitude Comissioners" and then the sextant was brought to Bird for inspection. Bird conclusion were that a) Division error on this sextant does not exceed 15", and b) A larger error would not escape his scrutiny. Most interesting is the second statement. How exactly did Bird examine the arc, remains an enigma, at least for me. Thus Bird himself recognized that machine division is more accurate than his own by a factor of at least 4. I should add that this 15" arc division accuracy exceeds (is better than) that of many modern sextants, judging by their certificates. Cassens-Plath claims 10" and SNO-T claims 12". But this is in their advertisements, not verified by any independent testing. While the very first machine-divided sextant was found to be accurate to 15" by an independent testing, in fact by a competitor:--) And on testing in Kew observatory: I have a paper describing the testing arrangement; apparently this equipment was installed in 1867. And indeed, I've never seen certificates older than that. I don't know when this testing was discontinued, but the middle XX century British sextants already have certificates issued by their manufacturers rather than by the Kew Observatory. Alex. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---