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: New Moon, Perigee, and Solstice
    From: Trevor Kenchington
    Date: 2003 Dec 29, 20:03 +0000

    We all make mistakes from time to time. The wisest amongst us have the
    grace to admit it when it is pointed out.
    You now claim:
     > I am sorry that my terminology caused confusion. I believe it was
     > abundantly clear from context that the "specific phase lag" I was
     > refering to was the phase lag between the solar and lunar constituents
     > of the tide.
    No Frank, that was not remotely clear. Your posting to which I replied
     >> The specific phase lag for Europe leads to a
     >> specific lag of the Spring Tides there.
    which any reasonable person would take to mean that what you intended by
    "phase lag" was _not_ the same thing as the lag between New or Full Moon
    and the date of highest spring tides. It is not a matter of my reading
    of your posting but one of your posting itself being, at best, misleading.
    You continued:
     > Anyone
     > with the slightest familiarity with the tides is aware of this, and I of
     > course am WELL aware of it.
    I am sorry, Frank, but there is no "of course" about it. You should not
    expect that any of your readers will assume that you have a deeper
    understanding of tidal phenomena than you display and, thus far, your
    postings to Nav-L have suggested a rather shaky comprehension.
    Next, you quoted my:
    > "Besides, if there was one
    > single phase lag for the entire region, it would not explain a
    > roughly-constant "age" of the tides throughout. That would need a
    > roughly-constant difference in the phase lags of the lunar and solar
    > semi-diurnal tides. Maybe that difference is roughly constant from
    > Ushant to the Shetlands but, if so, that seems a bit of a surprising
    > outcome from the complex of resonant systems over there."
    and responded:
    > In order to find it a little less surprising, maybe
    > you can think a little more about those inter-connected networks of
    > oscillators that others on the list have been describing. The main tide
    > in the northwest Atlantic couples to all of the smaller bodies of water
    > of the Channel, the Irish Sea, North Sea, etc.
    Of course the various amphidromic systems are coupled together, Frank. Of 
    course the semi-diurnal lunar ones all oscillate with the same frequency, 
    while their phase lags match at the points where they abut against each 
    other. Ditto for the semi-diurnal solar ones presumably, though I have never 
    seen cotidal charts for that tide. But why should the difference in the phase 
    lags of the semi-diurnal lunar and semi-diurnal solar tides be 
    (approximately) equal for (almost) all points in northwest Europe? 
    Postulating a "main tide" for the northeast (not your "northwest") Atlantic 
    and pointing to its linkage with the tides in lesser basins is irrelevant. 
    You are claiming that two independent tides, with slightly different 
    frequencies, interact with the shapes of those basins to produce oscillations 
    with phase lags that, while each varies from place to place (through the full 
    360 degrees), retain a steady difference from one another. That is not 
    impossible. It might be a chance conse
    quence of the shapes of the marine basins around northwest Europe. But the 
    odds of it happening must be incredibly small.
    I think you have misunderstood the cause of the "age" of tides and the reasons 
    why New England sees a different patterns from northwest Europe.
    Then you quoted my:
    > "Any notion that the tides of northwest European seas are dominated by
    > progressive waves (whether passing Spain or otherwise) should have been
    > laid to rest by 1900. On both sides of the Atlantic, the tides are
    > mostly dominated by amphidromic systems."
    > Well, yes, of course. I brought it up in connection with those early
    > navigation manuals and the discussion of errors on tides in Bowditch.
    > Understand now?
    I understand, Frank, that you have been caught posting an elementary error and 
    are now unwilling to accept responsibility. Look again at what you wrote in 
    the previous message:
    >> Another error in early accounts of the tides: In western Europe, the
    >> tide "wave" progresses up the coast starting in Spain and working its
    >> way north towards Ireland.
    You did not write that "early navigational manuals claim" or that "Bowditch 
    thought". You posted that "In western Europe, the tide "wave" progresses up 
    the coast". That is, quite simply, false.
    And then you turned to:
    > I didn't say there was any connection with the English Channel. George
    > H. suggested that Bowditch might have known about the three-day lag
    > because he had worked on translating Laplace. I was pointing out that
    > the work of Laplace up to that point (c.1800) could NOT address this
    > issue. See what I mean?
    Again: Look at what you actually wrote:
    >> The early hints from
    >> Laplace could explain differences along an idealized rectangular
    >> east-west channel (hence the reference to the English Channel you
    >> quoted)
    I'll accept that, in this case, your words could be interpreted as
    meaning "The early hints from Laplace were thought to explain
    differences along an idealized rectangular east-west channel such as the
    English Channel" (though I'm not sure that even someone in Laplace's day
    would have been so misguided as to think that). But I doubt that I was
    alone in reading your words as meaning "The early hints from Laplace can
    explain differences along an idealized rectangular east-west channel
    such as the English Channel". You had, after all, been invoking the real
    tides of the Channel and your supposition that Bowditch had learnt from
    accounts of the real tides of the area. Why invoke Laplace's theoretical
    treatment unless you supposed that it had some connection with observed
    tidal phenomena?
    Moving on to your response to my second message:
    With regard to my reasons for rejecting your claim that precise calculations 
    of the effects on tidal ranges of construction of a barrage were possible 30 
    or 40 years ago, you wrote:
    > But that's mere anecdote, Trevor. Interesting anecdote, of course. But it 
    doesn't invalidate what I wrote earlier.
    It was not intended to invalidate what you wrote earlier but rather to 
    disprove your claim. But of course you are right. I have only offered an 
    anecdote. That is more than you have offered in support of your bald claim 
    but it is still only an anecdote.
    Still, I decline the challenge to prove a negative. If you still insist that 
    precise estimates were possible before 1975 (even before 1990, if you 
    prefer), then you will kindly provide documented evidence in support. 
    Otherwise, I will take it that your claim was so much hot air.
    To end on a happier note, you asked:
    > Regarding land uplift in NB, do you know where the "zero point" is as you go 
    up the coast? All of the US East Coast has been sinking steadily for as long 
    as people have been keeping records. Relative sea level in southern New 
    England is rising at a rate of about 0.8 feet per century. Even in Eastport, 
    Maine, close to the Canadian border, sea level has been rising at something 
    like 0.7 feet per century. Do you know where it flips negative as you move 
    My understanding, from listening to Canadian geologists, is that the
    "zero point" in this region does not run east/west but more like
    NNE/SSW. New Brunswick is coming up out of the sea, the Atlantic coast
    of Nova Scotia is dipping into the water (by maybe as much as 5mm per
    year) and the "zero point" between is a line roughly following the Nova
    Scotian side of the Bay of Fundy.
    However, that same understanding includes the notion that southernmost
    New Brunswick is rising quite fast. (The only original research on this
    topic that I have ever read myself was a report on marine sediments in
    the bottom of lakes in that area.) Now you say that Eastport is going
    down at about 2mm per year. Since I doubt that the bottom of
    Passamaquoddy Bay is tilting sharply, at least one of us must have
    misunderstood or mis-remembered something along the way.
    I think I know where to go for a recent and authoritative description of
    current understanding of what is happening. If I can dig that out, I
    will post a summary.
    Trevor Kenchington
    Trevor J. Kenchington PhD                         Gadus{at}iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
                         Science Serving the Fisheries

    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