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    Re: Mid XIX century Nav
    From: Herbert Prinz
    Date: 2005 Nov 30, 19:40 -0500

    There are a few details in your statement that puzzle me. I realize that
    you are working from memory, but perhaps we can still get to the true
    core of Marguet's claim. I am unable to locate his "Navigation" in any
    library near me.
    The years 1774 - 1778.
    I presume you (or Marguet) meant to say "1774 - 1788". The French
    decided to include Lunar distances into the "Connoissance" from 1774 on.
    As you say, originally they were provided by Maskelyne. He and his two
    computers receive full credit in the explanatory part of the tables,
    although not in the "Avertissement", pp2-3, where the credits for all
    the other tables are usually given.
    Beginning with the edition for 1789, the distances were computed
    directly for the meridian of Paris. The workload had to be outsourced,
    being too much for the editor of the Connoissance (Mechain) alone.
    Marechal de Castries sponsored the enterprise in an effort to promote
    the usage of the Connoissance in the French navy and also in the French
    merchant marine. L'Emery was chosen to perform the computations. He
    seems to have been alone in this, although Mechain claims for the
    computations that "nous les avons toutes verifiees avec la plus grande
    attention". The distances were computed for midnight and noon of every
    day and interpolated for every three hours.
    Unfortunately, copies of the Connoissance for the years 1774 - 1778 are
    at the moment not available to me. A spot check of the editions for 1780
    and 1783 confirms that the reference meridian was Paris then, and I
    assume it always has been. Obviously, at least in this respect the
    tables were converted from the English original, but the otherwise the
    layout remained the same. Neither the two said copies nor any secondary
    sources that I am aware of  indicate that there has been any change of
    the mode in which the distance tables were copied from the beginning in
    1774 until 1789. But if there was indeed anything special about them
    during the first five years of their insertion into the Connoissance, it
    can only relate to their presentation, not to the question of being
    copies. Obviously, if you cannot confirm a typographical error, checks
    of the five editions in question are called for.
    The years 1800 - 1807.
    An unmodified copy of the English distance tables into the Connaissance
    of that time would have been an utter failure, because the English did
    not see the beauty of Vendemiaire, Brumaire, etc. all having the equal
    length of 30 days and preferred to count their days in the manner of the
    At any rate, the prefatory note in the copy for the year XIII
    (corresponding to 1804/05) states that the "distances from the moon have
    been computed trigonometrically by the Citizens Masson, Haros, Lenglet;
    and Citzen Mechain consented to assume the burden of directing and
    verifying all calculations and spent considerable and valuable time on it".
    Again, for the year XIV "distances from the moon have been computed
    trigonometrically by the Citizens Marion and Haros; and Citzen Delambre
    took the burden on himself of directing and verifying all calculations".
    Marion and Haros, by the way, also computed the places of the sun and
    the moon.
    These two copies are the only ones falling into the given period that I
    can check for now. Could Marguet have been talking about the planets?
    These have admittedly been pulled from the English almanac ("d'apres des
    verification", goes without saying!). The procedure was not totally
    effortless, because the arguments, (say, for Mars) day 1,7,13,.. in the
    Gregorian months did of course not correspond to 1, 7, 13, ... in the
    French months. The mismatch necessitated interpolation, whereas the mere
    adjustment for the meridian change would have been much simpler.
    The planetary tables underlying the ephemerides were entirely French.
    They came from La Lande's Astronomie, just like those of the Jupiter
    satellites (although from different editions). I do not know what the
    rational was behind the French decision to let the English do some part
    of the ephemeridal work, but not an other. Maybe the planets were not
    considered important. It is possible that they copied lunar distances in
    later years, but it does not seem very likely to me.
    Frank Reed wrote:
    >Also, you've reminded  me of something I read in Marguet's History of
    >Navigation. The French lunar  distance tables in the "Connaissance des Temps" were
    >once again copied from the  British Nautical Almanac from 1800 to 1807 (as they
    >had been previously, from  1774 to 1778). I don't know whether they were
    >adjusted for the Paris meridian,  which would be simple, or copied verbatim. In any
    >case, it means that Greenwich  was the sole independent source of lunar
    >distance data for navigators worldwide  in the early Napoleonic period.
    >[Marguet, "Histoire Generale de la  Navigation", 1931. No longer available at
    >the original web address. Originally  pointed out to Navigation-L by Wolfgang

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