Welcome to the NavList Message Boards.


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

Compose Your Message

Add Images & Files
    Re: Coordinates on Cook's maps
    From: George Huxtable
    Date: 2007 Apr 20, 08:19 +0100

    Alex, in Navlist 2644, referred to-
    | ... the paper by
    | Saul Moskowitz, The world first sextants,
    | (one of the very few good papers on the Inst of
    | Navigation CD you recently bought. In general,
    | Moskowitz is a rare exception among most of the authors
    | on this CD; his papers are substantial and interesting).
    I agree. But Moskowitz' two papers, on lunar distance and on sextants, are 
    not, by any means, free from error. It so happens that I was discussing and 
    listing suspected Moskowitz errors, in correspondence with Willem Morzer 
    Bruyns, last year. As I still have that list, it might be of interest to 
    I would be interest to get feedback, from Alex or from anyone else, 
    especially if he finds anything to argue with.
    here goes-
    Errors or suspected errors, and some comments, on two Moskowitz
    papers. Some are common to the two.
    Decimal parts of a page number indicate roughly how far down the page.
    L and R signify left or right column.
    The Method of Lunar Distances and Technological Advance, by Saul
    Navigation, Vol 17 No 2, pages 101 to 121.
    102.3L.  Should be Cotter not Cutter. It's given correctly in the list
    of references.
    102.8R. Gould rightly expresses his scepticism about such an unlikely
    tale when he adds "Credat Judeaus Apella", but Moskowitz just relates
    it as "a story told". Sobell characteristically tells it as a truth,
    but then she was just a journalist.
    103.0L. About the Shovell and other disasters, Moskowitz writes
    "Latitude was, almost, no problem". On the contrary, the Shovell fleet
    ended up on the rocks of Scilly on account of a failure of latitude
    rather than of longitude, although many have claimed otherwise.
    103.1R. I have read that Newton comment before, but not sure exactly
    where, and Moskiwitz gives no citation. But as I recall, Newton was
    commenting about timepiece longitudes, to which it was relevant, and
    not the Whiston and Ditton proposal, to which it was not.
    104.3L. The uselessness of Jupiter moons to a navigator is not because
    of defects in the theory, but because those moons are unobservable
    with any telescope that can be used at sea.
    104.8R. Not so. Maskelyne had presented two practical methods in the
    Tables Requisite in 1766.
    105.6L. "Flamsteed's salary was set at �100 a year, a magnificent sum
    ..." Deep irony here, presumably.
    106.6L. Mayer's tables were not for right ascension and declination,
    but for ecliptic longitude and latitude.
    106.7L. Campbell's sea tests were to check the practicality of the
    observations and the instruments; not the tables, which were checked
    on land by Bradley.
    106.9L. I think it was Maskelyne who arranged for the calculation of
    the lunar distances, not Mayer, after Mayer had provided tables
    showing how to predict the coordinates of the Moon.
    108.4L. There may be no mention in Phil'Trans., but there is in the
    Society's minutes for 1699.
    108.0R. "Errors in the latitude and longitude of known ports and towns
    were large enough to make accurate navigation unnecessary". a circular
    argument, and an untenable one. Positions were being determined on
    land with appropriate instruments, but the need was for an instrument
    that would do that job from an unstable platform at sea. That was what
    the 2-mirror instrument provided.
    111.0L. That quotation from Lind is so thoroughly absurd, it were
    better omitted.
    111.3L. The instrument shown in Fig. 9 is not as Mayer conceived it,
    but as Bird built it in brass (described later in thatparagraph). It,
    and the tables, appeared in 1754 not 1752.
    111.7L. Returning to the point of departure after a whole circuit (or
    circuits) was indeed a valid way to use a circle, but was not a
    procedure advocated by Mayer. All he asked for were several repeated
    observations, to be averaged.
    111.8L. "Unfortunately, Mayer's design placed the horizonn glass at an
    angle of 45 degrees to the axis of the telescope (as was the design
    practice for the Hadley quadrant)" No, it didn't, not for the Mayer
    circle or the Hadley octant, as illustrations show. If the mirror had
    been at that angle, then measurements to 90 degrees would have been
    113.7R. "By the simple expedient of placing the horizon glass almost
    right angles to the sighting telescope, the clumsiness of Mayer's
    circle was circumvented". That's complete nonsense. Borda saw that
    angles could be accumulated twice as fast by alternating between
    crossed and normal viewlines, with the reflected view on opposite
    sides of the telescope line. Mayer had not envisaged that possibility,
    and the telescope in his original wooden prototype was placed so as to
    obstruct a crossed viewline. However, in Bird's brass implementation
    of Mayer's design, the telescope has been pulled back, far enough for
    the circle to be used in just that way. Perhaps Bird had seen that
    possibilty himself. So the Bird version could have been used in the
    way that Borda later proposed, if anyone had thought to do so. The
    angling of the horizon glass didn't come into it.
    "The World's First Sextants", by Saul Moskowitz.
    Navigation. Title-page was headed vol 34, No. 1, Spring 1987, but
    later pages show vol 34, no.2, Summer 1987.  Pages 22 to 42.
    26.1. Not right ascension and declination, but ecliptic longitude and
    27.3. "Mayer's circle made by Bird for Bradley (see Figure 4)". No,
    figure 4 shows an engraving Mayer's original prototype, in wood, sent
    to London to be copied. Bird's instrument was based on that model, but
    differed from it in several important respects. The caption to fig.4
    is similarly wrong.
    27.5. "So as to return to one's point of departure upon the full scale
    (720 optical degrees)." Returning to the point of departure after a
    whole circuit (or circuits) was indeed a valid way to use a circle,
    but was not a procedure advocated by Mayer. All he asked for were
    several repeated observations, to be averaged.
            "Further, measurements of Lunar Distances of greater than 90
    degrees (the limit of Halley's quadrant) were then possible". No, it
    wasn't the repeating arrangement that made such angles possible, it
    was the correct angling of the horizon mirror.
    27.7 "Also, unfortunately, Mayer's design placed the horizon glass at
    an angle of 45 degrees to the axis of the telescope". No, it didn't,
    as a glance at fig. 4 clearly shows. "(as was the design practice for
    the Hadley quadrant)". No, it wasn't, as a glance at fig.1 clearly
    27.8 "a... a feature corrected on de Borda's design about 20 years
    later". It wasn't an error that needed "correcting". That was how
    Mayer designed it to be used. Borda's method of use was an
    improvement, but hardly a "correction".
    29.6. "John Bird made two sextants for the Board, Campbell's and one
    other, in addition to the Mayer circle, most probably the "... Three
    instruments ..." ordered by James Bradley in 1756." To clarify, that
    order in 1756 can't then have specified sextants, which were not even
    proposed by Campbell until 1757.
    33.9. "Sextant 1 has been shown in Ref.6 to have been the one made for
    Capt. Campbell in 1756". But it can't have been made in 1756, but
    1757, when Campbell proposed it.
    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. 
    To post to this group, send email to NavList@fer3.com
    To unsubscribe, send email to NavList-unsubscribe@fer3.com

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site