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    Re:       Re: Lewis and Clark lunars: more 1803 Alma nac data
    From: Dan Allen
    Date: 2004 Apr 21, 20:15 -0700
    My octant (an E. & G.W. Blunt circa 1830) has a vernier calibrated to 30" of arc.  The numbers on the arc are every 5 degrees from 0 to 105 degrees.  Perhaps it is too different and too new when compared with Lewis & Clark's sextant, but it is another data point.
     
    Dan
     
    -----Original Message-----
    From: Navigation Mailing List [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]On Behalf Of Bruce Stark
    Sent: Wednesday, April 21, 2004 6:06 PM
    To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    Subject: Re:       Re: Lewis and Clark lunars: more 1803 Almanac data

    You may have found it, Ken.

    You wrote: "
    But it's just way too close to
    the moon; 15°, in fact. Exactly 15°. Now I can't quite figure out
    what error would lead to the captains recording distances that were
    off by 15°, but for some reason the fact that there are no minutes or
    seconds in the error makes me think it's possible."

    The vernier on Lewis's sextant read to 15" of arc, so I'm almost certain the numbers on the arc would have been at 15° intervals. Also, the index mark of the vernier was almost certainly near the right edge of the "window frame" of the index arm. The 30° or 45° engraving they should have been reading the additional degrees, minutes and seconds from would have been outside the "window frame." Inside the frame, where the serious reading was done, 60° would have appeared.

    Perhaps, given the difficulty of reading a vernier sextant by firelight, or candle lantern, they picked up on the 60°, and counted from there.

    Does anyone have a 15" vernier sextant to test this theory with?

    Bruce

       
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