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    Re: More on Thomas Hubbard Sumner
    From: Ken Gebhart
    Date: 2005 Feb 11, 22:12 -0600
    Re: More on Thomas Hubbard Sumner on 2/11/05 7:22 AM, Jim Thompson at jim2{at}JIMTHOMPSON.NET wrote:

    -----Original Message-----
    From: Navigation Mailing List [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]On Behalf Of Frank Reed
    Sent: Friday, February 11, 2005 12:20 AM
    Subject: Re: More on Thomas Hubbard Sumner
    George H wrote:
    "What surprises me, is that it took until 1837 for navigators to realise
    that a useful position line could be drawn from a single observation of the
    altitude of a body, even if it wasn't at meridian passage."

    ... Plotting a celestial line of position would have seemed alien and inexact when first proposed.  

    And yet Sumner's pamphlet was ordered onto all US Navy ships the year it came out, although by then Sumner had spent 6 years verifying, refining and writing up his manuscript.  His pamphlet is still very convincing to read, partly because it was written so logically, and partly because it was verified with so many real examples by a practising ship's captain who used the method at sea himself.  At publication it had the endorsement of a highly regarded Harvard mathematics Professor, who had written to Bowdtich, so those clear-thinking experts, might have promptly focussed the navigation community on Sumner's discovery.  From Vanvaerenbergh and Ifland, we know that he had been talking about his ideas prior to publication.  It was rapidlly adopted in the UK, but only slowly in France, which explains perhaps why it was still there for Saint Hilaire, 40 years later.

    He opens his Introduction with this glorious single-sentence paragraph:

    "It is not so much the object of this work to present the navigator with a new method of 'Double Latitudes', as to afford him an accurate method of finding, by one Altitude of the Sun taken at at any hour of the day, wiht the Chronometer time, the True Bearing of the Land, the Latitude, &c., being, from any cause, uncertain; and to place him on his guard, when near a dangerous coast (and all coasts are dangerous when the Latitude is not accurately known) against those errors of Longitude by Chronometer, which arise from an erroneous Latitude used in finding the apparent time at the ship; directing, particularly, his attention to the fact, as shown in these pages, that when the Latitude is uncertain, a single altitude of the sun, at any time of day, whne not less than say 7 degrees high, is, with a good Chronometer, as useful as a Meridian Observation for Latitude ;  and the errors above alluded to are rendered apparent."

    In the Introduction, he also hints at extant navigators' thinking:

    "...the fact, that ship-masters universally understand, and daily practice the numerical calculation, namely, that of finding the apparent time at the ship, which is the only one used."

    "Many navigators, having taken morning sights for the Chronometer, supposing the observation useless without 'the Latitude', wait for the meridian observation, in order to deduce the Longitude by Chronometer; or, if the sun be obscured till afternoon, think a single altitude under such circumstances is of small value ; and, by the common methods, with good reason ; for then the Latitude by dead reckoning form the preceding noon, must, in general, be used to find the apparent time of the ship ; and here is the source of error ; because, 26 to 30 hours having probably elsapsed, in such time the ship may have sailed 250 to 300 miles ... cause an error in the Latitude by dead reckoning, and consequently in the Longitude by Chronometer.'  {Jim: we always talk about the "quest for longitude", but forget that in the early 1800's there was a less advertised and perhaps less understood "quest for accurate latitude".]

    "None of the works on Navigation, within the writer's knowledge, exemplify, or even hint at this important source of error" [Jim: he was referring to error in estimating longitude owing to error in dead reckoning the latitude, which was a necessary ingredient for calculating longitude] "but merely direct the observations be taken when the sun bears nearly 'East or West as possible', but it is impossible, for nearly 7 months in the year, to observe the sun in the East or West points."

    "It is hoped, that the 'Method by Projection', which explains these errors, and renders a single altitude, taken at any bearing of the sun, available, in a similar manner as a Meridian Observation, will supply a want which every practical navigator must have frequently experienced." [Jim: he was referring to accurate latitude.]

    I think his most convincing evidence is the last plate, which he mentions in the last sentence of his Introduction, almost as an afterthought.  It shows their trip from the Mississippi, through the Gulf of Mexico, around Florida and then north up the coast.  He was out of sight of land the whole time, and in waters plaqued with strong currents, which made dead reckoning treacherous.  His plate shows 3 tracks: (1) if done by dead reckoning alone (they would have thought that they had sailed past the tip of Florida and could turn north safely, if they had not grounded on Cuban beaches on the way, but in fact they were still in the Gulf and would have grounded at Tallahassee), (2) if done by dead reckoning modified by noon sights alone (miles out compared to #3), and (3) their true track made good, determined by using his procedures (tacked precisely between the Florida keys and Cuba).  Studying that chart, I imagine that any navigator of the day could see the advantages of studying the rest of the book.  I can imagine rushing into a tavern to show that plate to buddies, if only for the obviously interesting sea tale it told.

    Sumner was pleased with this plate because it proved how his method made it possible to more accurately calculate the various currents in the Gulf.  His mind really did soar -- he had found a better way not only to navigate, but also do to oceanography.

    On re-reading his pamphlet this morning, I was stunned to finally understand that he also clearly discovered the Celestial Fix!!  Page 11: "And likewise if two altitudes be observed, the times being noted by Chronometer, and the two lines, corresponding to the two altitudes, be projected as before, then both the true Latitude and the true Longitude is found at the intersection of the two projected lines."  Wow -- I had not heard that before about Sumner, but it only seems logical.  (I should have read Vanvaerenbergh and Ifland more carefully).  The term "line of position" did not surface until about 1866.  I don't know about the term "fix".

    He took brilliant advantage of special cases during his voyages.  In another example, his ship was becalmed at 25W, 44N.  Because he was basically not moving (about 1 knot, he wrote), his two sights varied primarily in time, about one hour.  The mid-morning sun's altitude climbed from 14 to 19 degrees.  He worked out the lat/longs of the two sights each twice, using latitude 43d and 44d.  That produced two LOPs subtended by a small angle.  "It is seen that these two lines intersect each other in Latitude ... which is the true Latitude, and the true Longitude is ...".  He had plotted a celestial fix, in January 1939.

    It seems to me as though the world then was ripe for the idea, hot tinder waiting for the match, as if everyone had it on the tips of their minds, but could not put it into practice.  Richardson suggests that another feature distinguishing Sumner was that, for some reason, he took the time out to nail his ideas down and finish a 25,000 word manuscript.  Perhaps other navigators had the same idea over years prior, but procrastinated, perhaps attending to ship's business, a snooze after lunch or a good novel, rather than hauling out old notes and going over them yet again.  So they lost the opportunity to beat Sumner to his well-deserved place in history.

    Just speculating,


    In the '60s I read a book by Arthur Koestler (Darkness at Noon, I think) entitled "The Sleepwalkers". It discussed many of man's inventions over hundreds of years, with the theme of "why didn't they see this sooner?".  It may answer some of the questions posed on this topic.

    Ken Gebhart
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