A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2016 Mar 16, 16:07 -0400
I've always had a great deal of curiosity about the Countinho Sextant.
Thank you for that diagram. It explains the optical path using the auxiliary mirror quite plainly. The bubble in the single spirit level is reflected off of the aux mirror.
Does the smaller horizontal aperture provide an unreflected, direct path to that same bubble in the same spirit level? Or is there an additional spirit level not shown in the diagram?
I went to the British Library in London yesterday to complete my registration. By way of a test of the facilities, I asked to see their rare(ish) copy of Francis M Roger’s ‘Precision Astrolabe’. The diagram of what you actually see through Coutinho’s artificial horizon was slightly easier to follow than the excerpts available on-line and in Peter Ifland’s book, so I took the attached photo. The diagram on the right-hand page doesn’t seem to include the smaller lateral spirit level visible in the drawings on the left-hand page. DaveP
Bill Lionheart wrote: There is a Japanese sextant on ebay http://www.ebay.co.uk/itm/Japanese-Tamaya-Sextant-serial-number-715-/291687942883?hash=item43e9f4cae3:g:TdsAAOSwe7BWt6Kh. I am intregued about the large triangualr box like structure near the horizon mirror. I wondered if it was some kind of artificial horizon?
Bill. The triangular attachment looks exactly like the “System Gago Coutinho” system. You can read all about its history, advantages, and disadvantages on pages 161-163 and Figures 171 and 172 of Peter Iflands “Taking the Stars”. The fact that Peter placed this particular device in the “Aircraft Celestial Navigational Instruments” section suggests the sextant on eBay might possibly have an aviation connection. DaveP
(Coutinho-Sextant-view-Large.JPG: Open and save)