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I am thoroughly impressed by Arthur Pearson's field test of the
calculated altitude LD method as used by Lewis and Clark. His
explanation is lucid and exciting. Well done!

Arthur asks:

> I would be most interested in any articles or books that document the
> use of these procedures by sea captains of the era as thoroughly as
> Preston and Gottfred document their use in the heart of the continent.

Andrew MacKay in his "Theory and Practice of Finding the Longitude at
Sea or Land" (London 1810) describes the method of calculated attitudes
for finding the longitude when the horizon is obscured. He recommends
the method particularly for use on land when the observer does not have
a proper artificial horizon.

While I don't believe MacKay had extensive sea going experience, his
text books on navigation were considered among the most authoritative at
the turn of the 19th century.

Paul Middents

   

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