NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: New Moon, Perigee, and Solstice
From: Trevor Kenchington
Date: 2003 Dec 29, 20:03 +0000
From: Trevor Kenchington
Date: 2003 Dec 29, 20:03 +0000
Frank, 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 included: >> 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 north? 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@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 http://home.istar.ca/~gadus