Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Bulges



In the System of the World (Book III of Principia), Newton clearly
indicates that there are two tides per day and draws an ellipse that
represents a cross section of the Earth (showing bulges on both sides).
He goes so far as to explain some unusual occurrences that had been noted
by sailors in Batshaw and the kingdom of Tunquin that, on the day
following the moon's transition from one side of the equator to the
other, there is only one tide per day.

In my quick perusal of this passage, however, I cannot find where he
explains why there must be bulges on opposite sides of the Earth.

My thanks to David Hamilton for this information. The kingdom of Tunquin
referred to is, I believe, the Gulf of Tonkin, off which are Haiphong and
Hanoi in North Viet Nam. I also seem to recall that the Adriatic has only
one tide per day, but my memory here may be as defective as it was about
Newton's perception of the tides. Any clarification would be gratefully
accepted.

The matter of tides on the real Earth depends strongly on the forms of
the basins containing the seas. Simple physical models are not used in
generating tide tables. To be useful such tables must be generated from
data compiled at the site over a long period of time and the analyzed for
the amplitudes of some well known harmonic components. Even then the
"errors" which occur can be large, since atmospheric effects (which are
not predicted far in advance) are important.

Leigh