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On Fri Nov 19 2004 - 19:53:20 EST Alex wrote:

>I made an unexpected discovery:
>Hadley's quadrant can be used as a dipmeter!

And on Sat Nov 20 2004 - 11:33:41 EST he wrote:

>I propose the following procedure for Index correction
>for back sights on land. It seems simpler, and independent

A little research shows that both discoveries are
not new (what else could one expect?).
They are both contained in the paper by
W. H. Wollaston, M.D., F. R. S.
"Observations on the Quantity of horizontal Refraction;
with a Method od measuring the Dip at Sea,
Phil. Trans., November 11, 1802.

(This is an extremelly interesting paper, in many respects).

Wollaston also says:
"This method of correcting the index error for the
back observation at sea, was many years since recommended
by Mr. Ludlam ["Directions for the use of Hadley's Quadrant,
1771, S 82, p. 56"]; yet I do not
find that it has been noticed
by the subsequent writers on that subject, or suggested
by any one for determining the dip..."

So Wollaston thought that the method of determining dip
was new in 1802. So did I yesterday:-)

Alex.

P.S. Phil. Transactions, which I combed today looking
whether they knew how to determine the dip with a quadrant,
contain great wealth of info on all CelNav subjects.
For example, the following paper addresses most issues
that are permanent topics on this list:

A Letter from the Rev. Nevil Maskelyne, MA, FRS to the
Rev. Thomas Birch, DD. etc., containing the Results of
Observations of the distance of the Moon from the Sun
and fixed Stars, made in a voyage from England to the Island
of St Helena, in order to determine the Longitude of the Ship,
from Time to Time; together with the whole Process of
Computation used on this Occasion,
read on June 24 and July 1, 1762.

A

   

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