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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Maury and Spooner on longitude at sunset
From: Frank Reed
Date: 2015 Oct 20, 18:02 -0700

In his post, Rommel wrote that he gave his friend "the link for Maury and sunset latitude" (presumably he meant longitude??). Does anyone know that "link" is? Did M.F. Maury at some point publish details of a method for using a sunset observation to get longitude? I don't recall seeing it in his 'Treatise on Navigation' published in 1845, but it's a common enough proposal.

A longitude by time sight calculation (or more generally a line of position) from an observation of the setting sun is certainly nothing novel or extraordinarily clever. In any navigation class that I have taught, at least one in ten students of navigation independently suggest the idea. You can use the altitude of the Sun at sunset, namely 0° 00.0', either upper or lower limb, and work it as an ordinary sight. The advantage, of course, is that it requires no sextant. But when is one likely to have all the tools of the trade for celestial navigation yet, by chance, no sextant? At best it fills a minor role. On a more general level, the trouble with such sights is that refraction right at the horizon is sufficiently variable that a sight like this can't be depended on for anything better than an "emergency" line of position. It can easily be in error by ten miles from variable refraction alone.

As for this claim that someone named Spooner thought of it first, well, sure, he may well have thought of it as some point. Many people have thought of this. It's a minor discovery, at best. The present source for the claim is a quaint book of collected Nantucket anecdotes published in the 1880s. Did Spooner publish his claimed discovery in any navigation resource? Apparently not. He merely boasted about it decades later. While it's certainly possible that he invented the idea on his own at some point, there's no evidence that I can see that he did anything with it, that he developed it into a proper technique, that he tested it out empirically over any length of time, or that he taught others to use this method. Therefore we're looking at a trivial and rather silly footnote on a minor topic in celestial navigation. Far from being some "wronged genius" in navigation, I see nothing here but an elderly mariner trying to convince his Nantucket neighbors that, once upon a time, he was really quite clever. Yes, indeed, as Bill suggested, "There once was a man from Nantucket, whose boast was so long he could..." Well, you know the rest.

By the way, there were many experts in nautical astronomy (the name used for celestial navigation in the 19th century) with Nantucket roots. They have not been hidden from history. One of the most important textbooks on the subject in this period was authored by J.H.C. Coffin (he was born in Maine but his family is an old Nantucket lineage). I've got two copies of the book on my shelves, and it's listed among the many historical works in the index that I assembled here. Speaking of Annapolis, as we have been recently, Coffin's textbook was the principal textbook in celestial navigation used at the US Naval Academy in the late 19th and early 20th centuries. Coffin was William Chauvenet's successor there. It's nearly impossible to reconcile the prominence of J.H.C. Coffin in navigation education with the proposed tale of a Nantucketer wronged by Matthew Fontaine Maury and ignored by the "establishment". If Spooner's tale had any merit at all, he would have had no trouble getting a hearing. As I say above, it sounds like little more than an old goat boasting to his neighbors... 130 years ago!

Frank Reed
Conanicut Island USA

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