A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sumner and the Smalls lighthouse.
From: George Huxtable
Date: 2006 Apr 4, 23:34 +0100
From: George Huxtable
Date: 2006 Apr 4, 23:34 +0100
I had written, about Sumner's Sun observation- |" The altitude, date and time of that Sun | sight would have been written into a permanent log, not just on a slate. As this | event was Sumner's proudest achievement, is it likely that he neglected to | retain that log, or at least transcribe a copy?" and Frank replied- | I think I understand the source of your misunderstanding now. It is simply | incorrect to state that a navigator would have recorded the "altitude, date, | and time" of every Sun sight. That DID NOT HAPPEN. Only in rare cases in 19th | century logbooks are the complete details of sights recorded. More generally, | only the final result is recorded in the logbook (for example, "Lat by Sun | at Meridian: 31d 22' "). You can check this out for yourself by examining any | of the logbooks from that era that are available online at | schooner.mysticseaport.org (the G.W. Blunt-White Library at Mystic Seaport). Once in a while, | you will find whole sights worked up from the initial observation, but this | usually only happens on the back of a page in a logbook, often from an entirely | different voyage (this would happen when the slate or the navigation | notebook has gone missing presumably). Even with lunar distances, it's rare for a | navigator to include all the details required to analyze the observations after | the fact. Very rarely, a "navigation notebook", like the one from the voyage | of the Morgan in 1896-97 that we discussed recently, will survive. But these | were literally nothing more than "scratch pads", and their survival, though | wonderful from our viewpoint today, is due to some descendant's packrat | habits, rather their intrinsic worth. They were not considered worth keeping in | the era. I accept that Frank is probably right about that, and not just as far as his special interest (American whaling logs) is concerned. | In his History of Marine Navigation, W.E. May notes that the position of the | lighthouse was plotted incorrectly by about five miles and then displays his | own plot. No noise about falsification. I quoted from May on Feb 17, and posted a copy of his pages to the Nav-l blackboard. May says "some miles", not "about five miles". May draws three "calculated positions" in his sketch. The only consequence that May deduces from Sumner's misplotting of Smalls light is that it would then place the "calculated second position" to seaward of the light, rather than to landward as May drew it. Did he appreciate the significance of the fact that in such thick weather Sumner could not have seen that light, in its true position? He doesn't mention it. So perhaps it's no surprise that he made "no noise about falsification". I wrote, in my earlier note, that I disagreed with some of May's analysis. Perhaps this is a good opportunity to explore what he got wrong. Sumner himself was inconsistent about his calculated positions, between which he would interpolate a position line. In his calculation on page 15 he takes two assumed latitudes, at 51deg and 52deg, and plots those on his chart at A and A' respectively. So just two calculated positions, 1 degree apart in latitude. In his descriptive text, on page 38, he explains what he did quite differently. First, he says he assumed his latitude by dead reckoning (presumably 51deg 37') and calculated his long. Then he tried a latitude 10' further North and calculated again. And then he tried a latitude another10' further North. So in this part of his account there were three calculated points, spanning 20' of latitude. And this is where he states that the three were all in a straight line. May states that Sumner "plotted these three positions on the chart" and adds, about the second of the three positions, that it was close inshore of Smalls light. In a footnote, May states that "Sumner shows it to seaward...". However, Sumner's sketch-chart shows nothing of the sort. It doesn't show those three positions at all; just A and A', miles away. So I don't know where May got that duff information from. Perhaps not from the original Sumner account and chart, but from a secondhand retelling, maybe one of those in Bowditch that have misled Nav-l members. Anyway, May got that quite wrong. Frank continued- | The basis of his "claim to fame" was the discovery and publication of a | navigational technique that was decades ahead of its time and would one day come | to dominate the world of celestial navigation. The specific events on that | day in late 1837 are a fascinating background to that discovery, but if we knew | nothing more of him than that story from that one morning, Sumner's name | would be forgotten. The story, it seems to me, was dramatised, to emphasise the point he was trying to make, at the expense of the literal truth. It doesn't detract from the importance of his discovery. But it diminishes the stature of the man, in my eyes and perhaps in the eyes of others. George ============= contact George Huxtable at firstname.lastname@example.org or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.