NavList:

Hi Douglas

Allow me to respond to your recent, ummm, posting.

(1) The only person who seems to think that you can get 1/10 minute of accuracy out of a sextant for normal observations seems to be you. Not one person has claimed that, although perhaps Henry or Chief Franklin, with thousands of observations may wish to speak to that topic. What we were discussing was obtaining 1/10 minute of INDEX ERROR. That is a specialized measurement and irradiation would not bother it, particularly since it will be a bright object compared to itself, be it the horizon, or the sun, etc.
(2) The article, which was clearly read and not ignored, speaks to un-magnified images. I check my index error using the greatest magnification, you probably do too. Frank's special trick for INDEX ERROR was 30 or 50X magnification, using a spotting scope. So, if the article talks to unmagnified images, and determination of index error uses highly magnified images, there seems to be a disconnect between the article and the intended observation.
(3) Dutton indicates that higher magnification tends to mitigate the irradiation. Dutton also goes on to state that irradiation could be present for an observation of the upper limb of the sun to the horizon, but is subjective, to your point. Dutton, of course, was used for quite some time at the United States Naval Academy, to teach US Naval Officers how to navigate. Perhaps we can take his advice!
(4) An unfortunate outcome of the NavList is that once you post, you cannot edit or retract your postings. Many have expressed a desire for this. Even I have been caught out, without thinking, just posting. Please try to remember, once you post, you post forever. I, too, was confused by your recent series of postings and apparent retractions. What Frank did was to provide a factual response to an incorrect observation. He may do that to anyone who posts something not factual. He's done it to me and to others. I am sure he didn't single you out for embarrassment. Its just a way to keep the list on topic and true to itself.
(5) I don't know why you continue to use George's name as the source of your irritation in your postings. George is a well known skeptic. He, himself, will tell you that he nit-picks things to death. Well, good on him. Nit pick away George! I, for one, appreciate his insight, nit-picky as it is.

In summary, you have presented what you think is evidence that irradiation affects all observations. For the specialized Index Error measurement, by the facts presented so far, it seems to be un-affected by irradiation. Magnification reduces irradiation effects, your evidence speaks only to un-magnified images. Hmmm, that doesn't sound like we are ignoring your evidence, does it? George gave you an even handed response.

I hope that you will consider this to be even handed as well.

Best Regards
Brad

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