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On 3 Jul 2008 at 21:27, George Huxtable wrote:

> Solving that problem calls for a different approach, because when the
> exact
> time is as yet unknown, neither are the exact positions of the bodies in
> the
> sky. That's why additional observations of the altitudes of the bodies
> were
> called for; or another technique, that of iteration, might be possible.

Two altitudes were needed, but there was no need for them to be of the
bodies used for the lunar distance. The practice of land navigators in the
18th and 19th centuries seems to have been to take an altitude of a body
that was either rising or setting for local time and a meridian altitude
for latitude. Even when the lunar was a sun-moon measurement (so that the
time sight used a sun altitude), the lunar was cleared with a calculated
altitude for the sun (i.e. no effort was made to extrapolate the measured
sun altitude to make it coincident with the measured lunar distance).

Ken Muldrew.

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