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You can read exactly what Gallagher said.
Thanks Ric. I'm not seeing mention of an eyepiece in the Gallagher exchange though. I do see the exchange here though:
http://tighar.org/wiki/Inverting_eye_piece_found_on_Nikumaroro Also does anyone know if sextants used only inverting eyepieces or did they sometimes also use erecting eyepieces as well?
I don't know but I do know that an inverting eyepiece is a standard sextant accessory for use in situations where you may want to move the observed celestial body up, rather than down, to the horizon.
I think we've been using the term incorrectly. I know nothing about Sextants, but from my knowledge of the terminology in astronomy, the term is somewhat of a misnomer. With a refracting optical design the objective lens (the lens at the front of the telescope) inverts the image. The basic eyepiece used with a refracting telescope does not correct this inversion but is unfortunately given the name "inverting eyepiece". If a person wants to correct the inverted image an accessory eyepiece or prism is needed, but this eyepiece is called an erecting eyepiece. So saying that it's an inverting eyepiece is equivalent to saying that it's a standard eyepiece rather than an accessory.
From the link above what Ross Devitt is describing is actually an erecting eyepiece rather than a standard inverting eyepiece.
"An inverting eyepiece would be at least an inch or so of metal & glass. The eyepiece is used to flip the sextant image so it is more 'natural' to look at (a sextant as you know will show the image upside down). An experienced navigator probably wouldn't bother using it" (Ross Devitt, December 14, 1999 Forum).
I think Ross has the terms mixed up, but he is right that an experienced navigator probably wouldn't bother using an erecting eyepiece because it's well know that erecting eyepieces use more optical elements and degrade the image. So what Gallagher probably found was the standard eyepiece that came with the sextant.
This probably has little relevance with the FN/AE disappearance, but it is good to know the differences between the eyepiece and what it is that Gallagher actually found.