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    Re: New Moon, Perigee, and Solstice
    From: George Huxtable
    Date: 2003 Dec 24, 16:14 +0000

    Frank Reed said-
    
    >Trevor, you quoted:
    >" "The "age" of the tide is due to the fact that on average over the earth
    >the solar tide lags behind the solar forces by a greater amount than the
    >lag of the lunar tide behind the lunar forces."
    >Which I think is the same as your explanation albeit in different words."
    >
    >Yes, I would say so.
    
    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. What is it about the Earth's hydraulics that can be
    so sharply "tuned" that its response is so very different, to two
    frequencies that are so nearly the same?
    
    Then followed a bit that Trevor partly omitted, a whole paragraph in
    brackets, which I think implies "second-thoughts", added when the original
    1941 volume was reprinted in 1980, as follows-
    
    "(At the present time, no wholly satisfactory explanation has been tendered
    for this world-wide phenomenon. Apart from the effects of friction, in any
    closed basin, if positive ages occur in one part, they should be balanced
    by negative ages elsewhere in the basin. It is possible, though it has not
    been dynamically proved, that this phenomenon is due to dissipation of
    energy in the coastal fringes.)"
    
    To me, the sacond sentence of that paragraph is particularly questionable.
    Given infinite resources, I reckon I could construct a suitable
    configuration that would disprove it.
    
    However, what is coming out of the paragraph quoted above is a
    back-tracking from the claim about the differing lags, to solar tide and to
    lunar tide.
    
    >And you quoted:
    >"However, the Manual continues:
    >"It is possible that this phenomenon [meaning the greater lag of the
    >solar tides, not the Age of the Tide directly] is due to dissipation of
    >energy in the coastal fringes."
    
    Reading again that full paragraph quoted above, it strikes me that it was
    trying to explain the "age of the tide" problem itself, and not the
    presumed greater lag of solar tides, contrary to Trevor's interpretation in
    sguare brackets.
    
    >That strikes me as no explanation. Why wouldn't that same logic apply to the
    >lunar tide? There's almost no difference between them. I think we're dealing
    >more with the basic phenomenon of phase lag in resonant systems.
    
    I agree with that.
    >
    >"and there must have been a
    >lot of relevant research in that time. Can you suggest somewhere I could
    >go for a fuller account of the cause(s) of the Age of the Tide?"
    
    Sorry, I don't know any sources that would help much.
    
    David Cartwright, in "Tides- a scientific history", offers little on the
    topic of the age of the tide. But he does refer to observations by Cassini
    of a sequence of tidal measurements he had initiated on the west coast of
    France, in 1710-20, at Brest and l'Orient, showing that there the spring
    tides followed full and new mooms by about 2 tides (age = 1 day) whereas at
    Le Havre and Dunkerque (Eastern end of the English Channel) it was 3 or 4
    tides (age = 2 days), "which he ascribed to the effects of propagation up
    the channel, as justified later theoretically by Laplace".
    
    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. Most of this work is in Laplace's book IV of
    Mecanique Celeste, which I understand is contained in the second volume of
    Bowditch's translation. However, I am not familiar with any of this
    material.
    
    George.
    
    ================================================================
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ================================================================
    
    
    

       
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