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 24, 17:36 EST
From: Frank Reed CT
Date: 2003 Dec 24, 17:36 EST
George Huxtable wrote:
"I find that "explanation" hard to accept. The period of the main component
of the solar forces is just 12 hours, and for the lunar forces it's 12
hours and 20 minutes. "
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.
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 Huxtable wrote:
"As Bowditch had undertaken the great task of translating all of Laplace's
works, it's no surprise that he was conversant with, and followed,
Laplace's tidal theories."
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.
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
"I find that "explanation" hard to accept. The period of the main component
of the solar forces is just 12 hours, and for the lunar forces it's 12
hours and 20 minutes. "
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.
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 Huxtable wrote:
"As Bowditch had undertaken the great task of translating all of Laplace's
works, it's no surprise that he was conversant with, and followed,
Laplace's tidal theories."
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.
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
