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: Frank Reed CT
Date: 2003 Dec 29, 17:30 EST
From: Frank Reed CT
Date: 2003 Dec 29, 17:30 EST
Trevor K wrote:
"I'm afraid you were badly off-base with this latest message."
I apologize that you found my message misleading. Please DO point out any errors as you find them, tough in the case of this message it appears to have been more a matter of your reading of my message. On to specifics...
I wrote earlier:
> It's a very simple issue. The ocean basins are a complex set of
> interacting oscillators. There are MANY resonant frequencies. A small
> difference in the frequency of the driving force *can* lead to a large
> difference in the amplitude of the response AND the phase lag of the
> response. Northwest Europe has a SPECIFIC phase lag that Bowditch copied
> from European sources (or maybe simply "knew" from the common culture of
> European sea lore). The specific phase lag for Europe leads to a
> specific lag of the Spring Tides there. That phase difference applies to
> much of northwest Europe, but it does not apply to the Americas generally.
And you replied:
"Northwest Europe most certainly doesn't have a "specific phase lag": the
times of HW literally span right round the clock just within the
Southern Bight of the North Sea, for example). Besides, if there was one
single phase lag for the entire region, it would not explain a
roughly-constant "age" of the tides throughout."
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. You are quite correct that the phases of the tide components vary greatly across even a small portion of Europe. Anyone with the slightest familiarity with the tides is aware of this, and I of course am WELL aware of it. This all got started because I pointed out that Bowditch wrote in early editions about Spring Tides occurring three days AFTER New Moon/Full Moon. That rule applies reasonably well in parts of northwest Europe. It does not work in most places and certainly not in New England which should have been familiar to Bowditch. So he copied an earlier European work. I was curious if anyone knew historical details.
You also wrote:
"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."
Yes, that's EXACTLY what we were talking about (not the issue you described above). 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.
I earlier wrote:
> 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. Early observers "guessed" that this was a
> general property of the tides worldwide, but it's not. For example, on
> the East Coast of the US, the tide cycle is almost simultaneous all up
> and down the coast --if it's high tide in New Jersey, it's high tide in
> South Carolina.
And you replied:
"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 also wrote earlier:
> No. Laplace's theories were only barely beginning to address the real
> ocean tides and would not have provided the kind of practical knowledge
> that Bowditch required for his navigation manual. The early hints from
> Laplace could explain differences along an idealized rectangular
> east-west channel (hence the reference to the English Channel you
> quoted), but they could not yet address the overall phase lag.
And Trevor you replied:
"You are right that LaPlace's tidal theories have little relevance to the
real tides in the oceans. However, you are way off base in supposing
that they have anything to do with the tides in the English Channel."
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?
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
"I'm afraid you were badly off-base with this latest message."
I apologize that you found my message misleading. Please DO point out any errors as you find them, tough in the case of this message it appears to have been more a matter of your reading of my message. On to specifics...
I wrote earlier:
> It's a very simple issue. The ocean basins are a complex set of
> interacting oscillators. There are MANY resonant frequencies. A small
> difference in the frequency of the driving force *can* lead to a large
> difference in the amplitude of the response AND the phase lag of the
> response. Northwest Europe has a SPECIFIC phase lag that Bowditch copied
> from European sources (or maybe simply "knew" from the common culture of
> European sea lore). The specific phase lag for Europe leads to a
> specific lag of the Spring Tides there. That phase difference applies to
> much of northwest Europe, but it does not apply to the Americas generally.
And you replied:
"Northwest Europe most certainly doesn't have a "specific phase lag": the
times of HW literally span right round the clock just within the
Southern Bight of the North Sea, for example). Besides, if there was one
single phase lag for the entire region, it would not explain a
roughly-constant "age" of the tides throughout."
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. You are quite correct that the phases of the tide components vary greatly across even a small portion of Europe. Anyone with the slightest familiarity with the tides is aware of this, and I of course am WELL aware of it. This all got started because I pointed out that Bowditch wrote in early editions about Spring Tides occurring three days AFTER New Moon/Full Moon. That rule applies reasonably well in parts of northwest Europe. It does not work in most places and certainly not in New England which should have been familiar to Bowditch. So he copied an earlier European work. I was curious if anyone knew historical details.
You also wrote:
"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."
Yes, that's EXACTLY what we were talking about (not the issue you described above). 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.
I earlier wrote:
> 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. Early observers "guessed" that this was a
> general property of the tides worldwide, but it's not. For example, on
> the East Coast of the US, the tide cycle is almost simultaneous all up
> and down the coast --if it's high tide in New Jersey, it's high tide in
> South Carolina.
And you replied:
"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 also wrote earlier:
> No. Laplace's theories were only barely beginning to address the real
> ocean tides and would not have provided the kind of practical knowledge
> that Bowditch required for his navigation manual. The early hints from
> Laplace could explain differences along an idealized rectangular
> east-west channel (hence the reference to the English Channel you
> quoted), but they could not yet address the overall phase lag.
And Trevor you replied:
"You are right that LaPlace's tidal theories have little relevance to the
real tides in the oceans. However, you are way off base in supposing
that they have anything to do with the tides in the English Channel."
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?
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
