NavList:

Frank,

You induce me to humbly, abjectly and sincerely apologize to the members of this List for daring to use the name Chauvenet in a posting, even if only intended as a comparative jest – certainly, to me, at least, NASA’s observers did not seem any more qualified than Chauvenet, a nuance apparently lost on you.  I said nothing about trusting his numbers any more than I trust NASA's numbers - by rough estimate, I have taken some 87,600 sights at sea in my time and do not, as the old saying goes, "steer by anybody else's compass".

 The mere mention Chauvenet's name, regardless of the context, appears to drive you into such a predictable frenzy as to place me in the category of a troll. Your tirades against Bro. Chauvenet are so familiar and repetitious as to lead to the suspicion that they are prerecorded or “canned” as boiler plate for immediate recovery and dispatch upon mention of his name. All may rest assured that, after this post, I will not mention his name again, if only for the sake of “peace and harmony”.

It would be difficult to deny the contributions made to the Art/Science of Navigation by the numerous astronomers and mathematicians of yesteryear who, with but few exceptions, had little or no time at sea in responsible positions; seafarers owe a lot to these gentlemen, and yes some ladies too, who provided much of the theory, math and instruction which they were challenged to make use of in the practical navigation of their vessels. Even the honored Bowditch most probably did not have a fourth of my sea time – does that place him in a lesser position than me? I really don’t think so.

Actually, the lightest amount of research will show that Chauvenet made no claims as respects originality in his statements regarding sextant errors of +/- 10”, as quoted in my post, but rather attributes this value to “the experience of good observers”. Certainly, as  Instructor in Navigation aboard the USS Mississippi and as a founder of, as well as Instructor at,  the US Naval Academy, he was in a position to discuss the results and experience of “good observers” with those very observers.

Regards,

Henry

--- On Sat, 3/13/10, Frank Reed <FrankReed@HistoricalAtlas.com> wrote:

From: Frank Reed <FrankReed@HistoricalAtlas.com>
Subject: [NavList] Re: Irradiation and manual navigation
To: NavList@fer3.com
Date: Saturday, March 13, 2010, 2:04 PM

Henry, you wrote:
"Isn't it really amazing how we seem to keep re-inventing the wheel. Didn't our "land bound" Professor Chauvenet give us the exact same number, i.e., +/- 10 arc seconds, in an 1868 paper on Astronomy - admittedly, however, he doesn't mention the matter of irradiation. Most of this stuff can be found in the literature of yesteryear."

Apples and oranges?

If anyone ever tells you that you should expect +/- 10 arcseconds in sextant observations with no further qualification, you should immediately ask, "what observations? what type of sextant? what telescope magnification? how many observations averaged?" There is no absolute number for the expected accuracy of observations, but there are some limits. The limit of the human visual system for standard resolution tasks (not vernier tasks) is about one minute of arc, slightly better in excellent conditions. If an observer gets unit magnification results for standard celestial navigation tasks un-averaged that are significantly worse than that, THEN something is wrong. Maybe the horizon is poor. Maybe there is some sort of operator error. Maybe even that ghostly apparition known as "Irradiation" is at work. Or maybe it's just a bad sextant.

As for Chauvenet, he had almost no experience in navigation. Though he was an exceptionally competent and meticulous mathematician, why would you trust his numbers on something like this? Are his works Scripture??

-FER

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