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Re: Re: Lewis and Clark lunars: more 1803 Almanac data
From: Bruce Stark
Date: 2004 Apr 21, 21:06 EDT
From: Bruce Stark
Date: 2004 Apr 21, 21:06 EDT
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
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
