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Dear navigator's, now that George tells us that explaining "two tides
per day" requires a lot of waving arms and legs, it makes me curious to
know why.

My simple understanding is that the centres of gravities of both earth
and moon, disregarding the sun, should remain at unchanged distances.
Therefore, when the moon pulls the water mass to one side of the earth,
it has to be compensated such that the centre of gravity remains
unchanged. That can be obtained by having an equal displacement of water
on the opposite side of the earth. I do recall that that opposite mass
is not precisely of the same shape, due to land masses disturbing the
equilibrium.
I am sure there is a lot more to it, but the prime reason suffices for
most people, I guess.

With fr. Gr. Eppo R. Kooi.

> -----Original Message-----
> From: Navigation Mailing List
[mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]
> On Behalf Of George Huxtable
> Sent: zondag 24 augustus 2003 15:38

> ............
> Geoff, tantalisingly, adds-
>
> >.. only leaving the question of why there are two tides per day
rather
> than one to be explained!
>
> Geoff's contribution sounds rather authoritative, and I wonder if he
would
> be prepared to respond to his own suggestion, in explaining the two
tides.
>
> Otherwise, perhaps I could recall (or reinvent) some of the arguments
I
> learned half-a-century ago, if anyone is really interested enough to
want
> to understand why there are two tides per day. If any listmembers
still
> find that a puzzle, and seek an explanation, I'm quite prepared to
have a
> go if requested.
>
> However, it usually needs several diagrams and much waving of hands in
the
> air, so it would be something of a challenge to do it in words only.
>
> George.

   

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