Comments for The Nautical Sextant

Comment on The USSR SNO-T sextant by engineernz

engineernz — Wed, 16 May 2012 08:07:19 +0000

It depends on how bright the sun is. My own practice is first to look at the sun directly through the shades (filters), to select a combination that gives comfortable viewing of the sun’s disc. Then I look at the horizon beneath the sun and do the same for the horizon shades. You can then set the instrument to zero and either look at the horizon beneath the sun and, as it were, take the horizon up to the sun, or find the sun (which may be uncomfortably bright if you find it in the left half of the field) and bring it down to the horizon. The second technique is my preferred method and it is almost essential to use it when shooting stars.

Practice makes you consistent and sometimes perfect .

Comment on The USSR SNO-T sextant by jame06366

jame06366 — Mon, 14 May 2012 17:42:17 +0000

Can you advice me which filters 1-3,4 index and horizon shades to use when taking the sun and some general advice for using shades?

Thanks
James

Comment on An Early C19 Ebony Quadrant Restored by Jean-Philippe Planas

Jean-Philippe Planas — Sun, 11 Mar 2012 08:43:25 +0000

A spectacular restoration. Thank you Bill for sharing this experience with us.
Jean-Philippe Planas

Comment on A Box Sextant by engineernz

engineernz — Tue, 31 Jan 2012 19:21:39 +0000

The safety of shades comes up periodically, in the context of worries about ultra-violet rays penetrating to and damaging the retina. In the 1960’s there were people who gazed at the sun under the influence of drugs and whose retinas on the whole came to remarkably little harm, and of course, there was their famous predecessor, Isaac Newton. Ultra-violet rays are quite well absorbed by ordinary glass and I would take the pragmatic view that if one can view the sun comfortably, the filters are satisfactory. Polaroid had not been invented in 1916 and, though older books write about a Nicol prism being used to reduce horizon glare, I have yet to see one. From about 1938 onwards, sextants were occasionally fitted with crossed Polaroids as shades, notably the US Navy Mark II, and I have an instrument from 1967 that has them, but I find that the view of the sun is just on the edge of being too bright for comfort.

Bill

Comment on A Box Sextant by Martin Hoskins

Martin Hoskins — Tue, 31 Jan 2012 10:26:33 +0000

Bill

Really facinating webpage, I have a 1916 Box Sextant by Frankham, it looks exactly like yours. I have been using a book by Jack Case as a guide, and am producing a small notebook of his rules for taking noon readings. I was interested to see the previous message about surveying as mine unit was used by the RAF, possibly for mapping airfields ?? so I would really appreciate a glimpse at it as well please.
I was wondering about your thoughts on the safety and effectivness of the filters for a unit of this age, it has the red and green, and in addition to the peep hole it has a minute dark filter, presumably pre polorizing?

Comment on Faking it. Is it a SNO-M or is it a C Plath? by engineernz

engineernz — Tue, 10 Jan 2012 19:26:02 +0000

Yes, Greg, The number at the zero end of the limb is Plath’s serial number. I don’t know exactly what the naval number indicates, but assume it is the unique identifier for naval stores purposes. Googling “Kriegsmarine” may help – and will certainly keep you occipied for many hours.
Bill

Comment on Faking it. Is it a SNO-M or is it a C Plath? by Greg

Greg — Tue, 10 Jan 2012 18:48:25 +0000

Bill,

I have one more question about my sextant. I noticed on the spreadsheet you sent (thank you by the way) You have in some cases a serial number and a Navy/Ship/Boat Number. I gather that the serial number is the number on the frame near the radius at the right hand end (“0″ end) of the scale and the Navy Number is on the Arm, under the “M”.

Any indication what the Navy number means? Or what it was used for?

Thanks again, you have been an awesome resource.

Greg

Comment on A Drowned Husun Three Circle Sextant by engineernz

engineernz — Fri, 06 Jan 2012 23:34:36 +0000

I will send you a picture to your e-mail address, Fabio.
My book does cover adjustment of the sextant and the principles of how they are calibrated.

Bill

Comment on USN BuShips Mark II sextant: some design oddities. by engineernz

engineernz — Fri, 06 Jan 2012 23:22:16 +0000

I have added some pictures of the cases by the various makers.

Bill

Comment on USN BuShips Mark II sextant: some design oddities. by Fabio Bram

Fabio Bram — Fri, 06 Jan 2012 07:32:41 +0000

Hi there.

Any pictures of the wood box and its contents (including key and locks)?

Thank you in advance.