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Quadrants, was: Preston's paper on Lewis & Clark's Navigation

Subject: Quadrants, was: Preston's paper on Lewis & Clark's Navigation
From: Trevor J. Kenchington (Gadus@XXX.XXX)
Date: Sun Jun 08 2003 - 08:11:47 EDT

George Huxtable wrote, as part of a much longer contribution:

> an octant in normal use can measure an angle
> up to 90° only (compare with 120° for a sextant).

Is that invariably true? I have seen at least one quadrant/octant with
dual peep holes. (The particular example that I recall is in the
Peabody-Essex museum in Salem, Massachusetts.) Using the second eye
position would still confine the instrument to a 90-degree arc but it
would not be the arc from 0 to 90, more like 30 to 120.

I have never read anything about such an instrument, nor how one might
be used, but it may be unsafe to simply assume that any quadrant was
incapable of measuring altitudes greater than 90 degrees.

Trevor Kenchington 

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Trevor J. Kenchington PhD                         Gadus@XXX.XXX
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