NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brendan Kinch
Date: 2014 Jan 17, 23:54 +0100
If I remember correctly, the prism splits the star (being observed) into two stars and it apparently is easier getting the horizon in the middle between the two stars you are seeing rather than as normal, getting one star to touch the horizon to take the altitude.
The theory may not have been altogether true as the prism did not appear to be all that popular…..well, we don’t see many of them do we? OR….maybe they were too expensive to add to the ‘run of the mill’ sextants that were in use.
Kinch
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Brad Morris
Sent: 17 January 2014 23:23
To: BrenKinch@gmail.com
Subject: [NavList] Re: Chasing Shackleton
Kinch
That scope rates a wow! Probably a star scope for its light gathering characteristics.
Why would you want a Wollaston prism on a sextant? Anybody?
Brad
On Jan 17, 2014 4:37 PM, "Brendan Kinch" <brenkinch---.com> wrote:
Hi Brad…..for sure the frame and parts were supplied by Heath even though it says “Sewill. Maker to the Royal Navy. Liverpool”. Sewills also ‘made’ chronometers – but inside they were really Mercer . Not unusual and the Heath frames are seen with many different maker’s names. I am a collector (as well as ex navigator) so I see many different types with very similar traits here and there. (Just look at the swing arm also on the Sewill).
The handle is full ivory – another photo attached.
I have another – Bell frame by Heath, New Eltham, that has the huge scope as on yours but one of the more interesting ones is the one by Loriux a Hurlimann, Paris…..look at the scope on this one… (see attached). Another nice feature on this one is the Wollaston Prism; see it just above the 4 index shades.
Kinch
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Brad Morris
Sent: 17 January 2014 21:13
To: BrenKinch---.com
Subject: [NavList] Re: Chasing Shackleton
Kinch
Those binoculars look exceedingly familiar, right down to the method of attachment. Is it a Heath sextant? Much of the other characteristics say it is a Heath as well.
I'm also interested in the handle. You say it is of ivory? The entire handle or just a piece for marking down observations, like a white board?
It is certainly a beautiful!
Brad
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