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While studying the pictures
of Hadley quadrants to answer Omar's
questions, I made an unexpected discovery:

Hadley's quadrant can be used as a dipmeter!
To see this, read carefully the beginning
of p. 178 in Norie:
(go to
http://www.mysticseaport.org/library/initiative/
ImPage.cfm?BibID=13617&ChapterId=1
Then click on "description and use of Hadley's quadrant"
on the left, then go to page 6, and read
IV. To set the Back Horizon Glass perpendicular to the
plane of the Index Glass, 0 on the Nonius being at 0 on the Arc.)

Once this is done, the Back Horizon Glass is set
perpendicularly, you can use the VERY SAME procedure
to measure the dip!

This shows how one can attach ONE extra horizon mirror
(and a sighting
vane or a second telescope mounting bracket) to a
sextant
to convert it to a dipmeter:-)

Unfortunately, modern sextants are just a little
bit too short to do this conveniently: you won't
be able to wear a hat, and some maybe will have to shave
their hairs:-)

Alex.

P.S. Norie never mentions this possibility.
But it is hard to believe that I noticed this first:-)

   

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