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George,

Interesting question.

I'll take a guess that the common layout of the sextant was based on
that of Hadley's quadrant, which itself was primarily intended for Sun
sights, for which the convenience of looking horizontally outweighs
other considerations. If so, your question could be re-phrased as: Why
did the form of sextants not evolve to make them easier to handle for
lunars and for star sights?

The star sights may be easily answered: If most mariners pre-computed
their twilight sights, inverting the sextant to find a particular star
will have been too unusual to merit a major re-design of the instrument.

That leaves lunars, for which I have no such simplistic answer. Reading
the on-running threads amongst the "lunartics" on this list, I am often
left trying to visualize navigators, at sea under sail, contorting
themselves in an effort to get highly-precise measurements of distances
between awkwardly-placed celestial bodies, half-obscured by sails and
rigging and I just can't picture that. I would expect that memoirs of
the time would mention the awkward observations but I am not aware of
any that do. Is it possible that the rare lunar observations (and we
know they were rare) were normally only made when the required distance
could be measured _without_ awkwardness?


Trevor Kenchington



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Trevor J. Kenchington PhD                         Gadus@iStar.ca
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