Salusbury, Thomas Mathematical collections and translations 1667

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396
no cause of ebbing and flowing, save onely by the participation
of another Sea, wherewith it hath communication, that is sub­
ject to great commotions.

The cause why
some Seas, though
very long, suffer
no ebbing and
flowing.

Ebbings and
flowings why grea­
test in the extre­
mities of gulphs,
and least in the
middle parts.

In the fourth place we shall very easily find out the reason
why the fluxes and refluxes are greatest, as to the waters rising
and falling in the utmost extremities of Gulphs, and least in the
intermediate parts; as daily experience sheweth here in Venice,
lying in the farther end of the Adriatick Sea, where that diffe­
rence commonly amounts to five or six feet; but in the places
of the Mediterrane, far distant from the extreams, that mutati­
on is very small, as in the Isles of Corsica and Sardinnia, and
in the Strands of Rome and Ligorne, where it exceeds not half a
foot; we shall understand also, why on the contrary, where
the risings and fallings are small, the courses and recourses are
great: I say it is an easie thing to understand the causes of these
accidents, seeing that we meet with many manifest occurrences
of the same nature in every kind of Vessel by us artificially com­
posed, in which the same effects are observed naturally to fol­
low upon our moving it unevenly, that is, one while faster, and
another while slower.

Why in narrow
places the course
of the waters is
more swift than in
larger.

Moreover, considering in the fifth place, that the same
quantity of Water being moved, though but gently, in a spatious
Channel, comming afterwards to go through a narrow passage,
will of necessity run, with great violence, we shall not finde it hard
to comprehend the cause of the great Currents that are made
in the narrow Channel that separateth Calabria from Sicilia:
for that all the Water that, by the spaciousnesse of the Isle,
and by the Ionick Gulph, happens to be pent in the Eastern
part of the Sea, though it do in that, by reason of its largeness,
gently descend towards the West, yet neverthelesse, in that it
is pent up in the Bosphorus, it floweth with great violence be­
tween Scilla and Caribdis, and maketh a great agitation. Like to
which, and much greater, is said to be betwixt Africa and the
great Isle of St. Lorenzo, where the Waters of the two vast
Seas, Indian and Ethiopick, that lie round it, must needs be
straightned into a lesse Channel between the said Isle and the
Ethiopian Coast. And the Currents must needs be very great
in the Straights of Magellanes, which joyne together the
vast Oceans of Ethiopia, and Del Zur, called also the Pacifick
Sea.

A discussion of
some more abstruse
accidents observed
in the ebbing and
flowing.

It follows now, in the sixth place, that to render a reason of
some more abstruse and incredible accidents, which are obser­
ved upon this occasion, we make a considerable reflection upon
the two principal causes of ebbings and flowings, afterwards
compounding and mixing them together. The first and simplest