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Ken, you wrote:
"Now that this thread is coming to a close"

More likely, a brief lull. :-)

You asked:
"can the following questions be answered?
1.  Does normal sextant use, even by a neophyte, pose any significant
risk of eye injury?  (I use the term significant, because we all know
we are damaged by cosmic radiation, UV, second hand smoke, lead, beer
and any number of other things with which we have daily contact.  I
am not concerned with this level of danger.)"

NO. Sextants are comparable to binoculars as far as eye risk is concerned. One 
might argue that a sextant is different because the user is *encouraged* to 
point it at the Sun, but of course it also comes with all the appropriate 
shades. A "neophyte" using binoculars or a sextant might aim either at the 
Sun for a moment (with the sextant's shades not in place) but the normal 
reflex to look away from bright light would work as normal, and there's no 
time for damage. If the neophyte is somehow profoundly confused and believes 
that he is supposed to "put up with" pain in the eyes --no pain, no 
navigation (!!)-- then said neophyte could in fact damage his eyes. I would 
not call such strange behavior "normal sextant use" but a lawyer could 
probably convince a jury otherwise. This sort of risk falls somewhere between 
"warning: second-hand smoke may make you sick one day" and "warning: this cup 
of hot coffee may be very hot". The day may come when lawyers and/or 
bureaucrats in Brussels and/or Washington decide that, for our best 
interests, sextants, binoculars, and all sorts of telescopes must come with 
terrifying warning labels.

And:
"2. Does the risk of eye injury increase with the addition of a
magnifying scope?"

YES. The image of the Sun is larger in proportion to magnification. The 
intensity at each point in the image is NOT increased so the cause is not 
from "brighter" light, but from greater total area experiencing light of the 
same brightness (a model which would fit this, though not necessarily the 
correct one, is simple cooling by conduction: the area receiving sunlight 
increases with the square of the magnification while the boundary of that 
area, which is the part that is exposed to cooling by conduction, increases 
only linearly with magnification). If you look at the Sun for one full second 
with your unaided eye, without magnification, you will not damage your eyes. 
If you look at the Sun through a 7x sextant telescope for one full second, 
you will probably damage your eyes (leading to blind spots lasting for months 
if not permanent).

-FER



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