NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: System Gago Coutinho
From: Gary LaPook
Date: 2010 Feb 15, 16:56 -0800
From: Gary LaPook
Date: 2010 Feb 15, 16:56 -0800
Yes. gl Frank Reed wrote: > > Gary, you wrote: > "I am attaching an excerpt from the book "Precision Astrolabe" that > describes the Coutinho sextant and other sextants adapted to aviation > use." > > Thank you. That's a rather rare book. Copies on Abebooks.com are > selling for about $65 and up. Could I ask you to post pages 192-193? > They don't seem to have made it into your sextants.pdf file. > > This book, as well as another which I found through google, stress > that the key feature that was novel at the time was that the Gago > Coutinho bubble horizon employed a spirit level which was curved in > just the right ratio so that if the sextant is pitched up and down > (rotated about an axis perpendicular to the sextant frame and passing > through the eye-end of the sighting tube or telescope) the image of > the Sun or star and the bubble remain together much the same as with > respect to the sea horizon in a standard marine sextant. This was > standard in later bubble sextants, but back then it was apparently a > big deal. Also, the diagrams in the pages you posted clear up one > other puzzle. In photos of his original prototype and also of the > production Plath versions, the housing for the bubble and the mirror > appear to be behind the mirrored part of the horizon glass, and we can > even see that the usual horizon shades are available for the clear > part of the horizon glass. The bubble housing does not block them (not > completely at least). According to the book, the horizon mirror of the > Gago Coutinho type of sextant was unique in that the horizon glass was > divided into three parts. Only a small central section was fully > mirrored. The section away from the frame was clear and allowed a view > of the sea horizon if available. The section near the frame was also > clear and allowed a clear view of the bubble. Of course, all three > sections could reflect the image of the celestial body. > > -FER > > ---------------------------------------------------------------- > NavList message boards and member settings: www.fer3.com/NavList > Members may optionally receive posts by email. > To cancel email delivery, send a message to NoMail[at]fer3.com > ---------------------------------------------------------------- >