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Alexandre Eremenko quotes my rhetorical question

> "Now, how does the size of the mirror come into play?"

and kindly answered it

> It permits you to move your eye up and down substantial
> distance, (42 milimeters approx.)
> without loosing the view of both visors.

Alexandre could have spared himself the trouble if he had noticed that
the full quote actually was:

"Now, how does the size of the mirror come into play? It may amplify an
effect that is
already there, mainly because it allows wider vertical viewing angles,
[...]"

Although I am grateful for the elucidation that my expression "allowing
wider vertical viewing angles" means that you can "move your eye up and
down a substantial distance", I must stress that the main point of my
comment was actually in the subsequent sentence: "But a large mirror by
itself does not create the effect."

This was in direct response to Alexandre's false claim that every sextant
suffered from this problem.

Alexandre has actually stated that he has a mathematical demonstration
for this claim and offered to divulge it. I, for one, would be very
interested to see it. Others, too, have expressed an interest. I realize,
of course, that Alexandre has changed position on this issue, confronted
with the fact that there are real world objects (sextants, to wit) that
contradict the claim. But where does this leave geometry? As our Pope
says "Truth cannot contradict truth".

Herbert Prinz

   

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