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    Lunars - Finding Bermuda in 1807
    From: Frank Reed
    Date: 2007 May 12, 21:32 -0400

    Greetings, Fellow Lunatics.
    As a preamble, I will note that June 22, six weeks from now is the 200th
    anniversary of a naval encounter known to historians as the
    Chesapeake-Leopard incident in which HMS Leopard fired upon the American
    frigate Chesapeake after insisting on the right to board her and search for
    British deserters. The commander of the Chesapeake surrendered his vessel
    after scarcely any resistance. The British commander refused the surrender
    and boarded as originally intended, taking away a few sailors, one of whom
    was later hanged for desertion from the Royal Navy. There was considerable
    outrage in Washington over this incident, both the boarding and the swift
    surrender of the Chesapeake, but at the time, it was only a "seed" for the
    upcoming war, known today as the War of 1812.
    Later that same summer, in mid-August of 1807, HMS Leopard stopped another
    American vessel, the Erin, a small, fast merchant vessel transiting from
    Bordeaux to Baltimore in defiance of the British blockade of Napoleonic
    France. The navigational details of this particular incident were described
    in detail by Basil Hall, at that time an 18-year-old midshipman who was
    placed in command of the Erin as "prize-master" and ordered to take her to
    Bermuda for adjudication.
    Basil Hall wrote a series of books describing life in the Royal Navy in the
    early 19th century. These books were an important resource for Patrick
    O'Brian and apparently provided much of the period detail in his novels. A
    few of Basil Hall's books are available on googlebooks. The one which I
    quote below in not among them but there are portions of it quoted in yet
    another book.
    Here is Basil Hall's story of lunars in 1807:
    "When I was mate of his majesty's ship Leopard, I was placed in charge of
    the identical ship which carried Jerome Bonaparte and his family to Europe,
    and selected for that purpose from being considered the fastest sailer out
    of Baltimore. I certainly never saw a more perfect model of a merchant
    vessel or one more commodiously fitted up. I was, of course, prodigiously
    proud of my new and beautiful command; but had soon more important matters
    to attend to in the navigation of the ship.
    "When we parted company with the Leopard, we were within a few days' sail of
    the coast of America, and may then have been a hundred leagues or so to the
    north-westward of Bermuda; consequently, still within the influence of the
    Gulf Stream, already alluded to as sweeping, in a north-eastern direction,
    along the shores of the United States. I was ordered to take my pretty
    charge to Bermuda and proceeded to the southward accordingly. Foul winds,
    however, detained us for several days in the Gulf Stream, for the set of
    which current such an ample allowance was made, that when we reached the
    latitude of Bermuda, 32 1/2 N., it seemed almost certain that we were some
    thirty or forty miles to the westward of the island, that is between it and
    the coast of America.
    "From the land of Bermuda being low, it is not easily got sight of; and the
    whole cluster of islands beging of small extent, they are often missed by
    navigators steering, as they conceive, directly for them. To those, indeed,
    who are provided with time keepers, there is no danger in following this
    direct method; for these instruments are now so admirably constructed, that
    an error in longitude which would carry a navigator past Bermuda, without
    seeing it, is, now-a-days [Hall is writing in the 1820s], very unlikely to
    occur. Ships, however, which have not the advantage of a chronometer, and
    consequently may not be sure of their longitude, generally find it prudent
    to run into the latitude of the island, and then steer along that parallel
    till they come in sight of their object. Most people are probably aware,
    that the latitude is an element of navigation almost at all times very
    easily determined, at least with sufficient accuracy for the purpose now
    alluded to. The longitude, as every mortal must have heard, is, or rather
    was, the grand stumbling-block in a sailor's way; and it will readily be
    understood, of what essential importance it must be to a ship, when running
    along a parallel of latitude, in search of a mere speck on the ocean, like
    Bermuda, that there should be no mistake as to which side of the island she
    really is upon. For if, in point of fact, the ship shall happen to be on the
    eastern side of the island, but, owing to some error in the reckoning, her
    captain believes that she is on the western side, he will naturally steer
    east along the parallel of latitude, instead of west, as he ought, of
    course, to do; and thus will go on increasing his distance from the island,
    instead of shortening it.
    "This curious case was precisely mine. The Gulf Stream, as it eventually
    appeared, had carried us eighty or ninety miles farther to the eastward than
    I had made allowance for, although an ample daily set in that direction was
    given her. The superficial velocity of this mighty current, it seems, is
    occasioneally accelerated or retarded by the prevalence of hard gales. At
    all events, whatever might be the cause of this unusual increase in the rate
    of the stream, it carried me so far beyond my mark, that when I reached the
    parallel of 32 1/2 N., I supposed myself in longitude 65 1/2 W., that is,
    about forty miles on the western or American side of Bermuda. As the wind
    was blowing from the east, of course I struggled hard to beat up against it,
    from supposing that my port lay to windward. It was fortunate that this
    breeze was not blowing from the west, as I shall proceed to show.
    "On the day I reached the latitude of Bermuda (32 1/2 N.), I fancied the
    ship must certainly be on the western side of the island; the sun, however
    happened not then to be in distance, as it is called, and, of course, no
    lunars could then be observed. Having, therefore, still nothing to trust to
    but the dead reckoning, we, of course, continued beating all the morning to
    the eastward, under the full persuasion that Bermuda was in the wind's eye,
    due east of us, instead of being, as it really was, due west, on our
    "As the night approached, the sky became beautifully clear, and shortly
    after sunset I got my sextant to work. Before the twilight was ended, and
    the horizon too faint to admit of the altitudes being taken with accuracy, I
    had observed four or five sets of lunars. No time was lost in working out,
    when, lo and behold! the longitude, instead of being 65 1/2 W., as I made it
    by dead reckoning, appeared to be little more than 64 W., or some ninety
    miles farther to the eastward; thus showing that, although, as we supposed,
    we were thirty miles from the land it was on the opposite side of the island
    from that on which we had imagined ourselves to be!
    "What was now to be done? For, although on board the flag ship, where the
    accuracy or inaccuracy of a midshipman's lunars did not matter a straw, I
    had indulged in the usual presumption of fancying myself rather an expert
    observer, I was now filled with doubt and anxiety. All the ordinary
    allowances for the set of he Gulf Stream had already been made, and it was
    hardly to be conceived that in a week or ten days there should have occurred
    an error of a degree and a half. It appeared far more likely that some gross
    mistake had been committed in the figures of the computation, or in my mode
    of observing the lunars, than that such a huge augmentation to the strength
    of the current should have occurred at this particular moment.
    "The American captain, who, like most commanders of ships of that class
    sailing from the United States, was an admirable navigator, and a very
    shrewd, obliging, and gentlemanlike person, happened to be so ill that he
    could not possible come on deck, to make observations to corroroborate mine.
    But he was able, though in bed, to go over the computations, the result of
    which, in his hand, agreed so nearly with what I made it, that he, at least,
    had no doubts of their accuracy, and recommended me at once to put the helm
    up, and steer to the westward. I had not confidence enough, however, in my
    own handiwork, for a decision so material to the success of the voyage. In
    short, I could not force my unpractised imagination to conceive that an
    island, which I had so much reason to suppose lay due east of me, could
    possibly be hit upon by steering due west.
    "So, to work I went again, with my observations for the longitude. After all
    the adjustments of the sextant had been carefully examined, a new gang of
    lunars was taken, some with the same, and some with other stars, but all of
    them with a degree of attention which, if measured by the depth of interest
    felt in the result, I am not sure I have ever bestowed upon any similar
    course of observation since. Half of the distances I gave over to my friend,
    the captain, to compute, while I set about calculating the rest. After a
    time we exchanged computations, without communicating each other's results,
    till all were finished, and then we laid them side by side. The agreement
    amongst the whole observations was so near to one another and corresponded
    also so closely with those taken earlier in the evening, that I could no
    longer have a doubt as to what should be done. About midnight, with a
    throbbing heart, and a mind filled with the most painful anxiety, I bore up,
    and, as we had a fresh breeze, spanked along merrily to the west. It was
    necessary, of course, in running in such a perilous neighborhood, to keep a
    very bright look out; for although Bermuda, on its eastern side, is pretty
    clear of coral reefs, and we were quite certain of our latitude, it was not
    the sort of place to approach incautiously. When the moon went down,
    terefore, we shortened sail, but continued still slipping along at the rate
    of four or five knots, till morning.
    "When the eastern sky first began to give some faint promise of a dawn, I
    felt my anxiety mount to a pitch scarcely bearable, and I kept peering with
    the night-glass into the gloom which still hung over the horizon in the
    supposed direction of Bermuda, as if my eagerness to see what was hid
    beyond, could have brushed away the night any quicker. When, at last, the
    day broke, and the well-known cliffs of St. David's Head, topped with dark
    green cedars and lighter-tinted orange trees, stood pleasantly up ahead of
    us, at the distance of a league and a half, I could have shouted with joy.
    "I was not a little amused by finding we had reached the island before our
    own ship, and, a few days afterwards, I had the satisfaction of rowing on
    board to report myself, before she anchored. The compliments paid to our
    success were due, it must be owed, to the sextant so opportunely sent to me
    for, unless the dead reackoning had been checked by lunar observations, we
    might have been kept at sea a month; and, as the ship was short of
    provisions, serious consequences must have ensued."
    And that ends Basil Hall's account of these events. It's interesting that
    Hall did not give more details regarding the American vessel he was
    commanding. He did not name it in his book. I asked on H-Maritime (a
    low-volume maritime history list) if anyone knew the name and found soon
    enough that it was the Erin. With that clue, I discovered several other
    fascinating references through google books including a short article
    written in 1919 providing some details ("An Early Baltimore Clipper: the
    Capture of the Erin"), and a letter written by the British Consul in
    Washington in March, 1805, when Jerome Bonaparte sailed with his young
    American wife from the US to Lisbon. From that letter, we have this
    description of the Erin: "She is a fine small Ship, sails very fast, bright
    sides, white bottom, black Wales, yellow Gun wale, dead eyes yellow, no bull
    work a midship, and a figure head". I can almost see her now... She was a
    vessel of 213 tons and unusually fast, typical of the Baltimore Clippers
    which would soon become famous as privateers and traders and infamous as
    slavers. The Erin had previously served as a diplomatic courier for the
    Spanish between Europe and the Caribbean. Just before the events Basil Hall
    desribes, she had left Bordeaux with a cargo of brandy, wine, and dry goods
    on June 26, 1807 and was detained by HMS Leopard on August 13, 1807. The
    captain, whom Hall speaks of so highly, was William Stevenson. The lunar
    observations described by Hall must have taken place on the night of August
    20-21, 1807, give or take a day. As he says, the Sun was "not in distance",
    so he was compelled to se the stars for lunars, apparently much less popular
    among practical navigators.
    I think this story is a nice example of the transition from dead reckoning
    navigation to celestial navigation. Hall clearly believed rationally that
    lunars worked, but this was an era when navigators had great faith in dead
    reckoning. They trusted it, and it took a revolution in their thinking to
    trust sextants and mathematical tables more than the log and the feel of the
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