Archimedes Texts

395
flowing is wholly annihilated, or at least very much obscured.
I passe by the continual alteration of the air, which disquieting
the water, permits us not to come to a certainty, whether any,
though but small, encrease or abatement of half an inch, or
lesse, do reside in the Straights, or receptacles of water not a
bove a degree or two in length.

Reasons renew
ed of the particu
lar accidents ob
served in the eb
bings and flowings.

I come in the second place to resolve the question, why, there

not residing any vertue in the primary principle of commoving
the waters, save onely every twelve hours, that is to say, once
by the greatest velocity, and once by the greatest tardity of
motion; the ebbings and flowings should yet neverthelesse ap
pear to be every six hours. To which is answered, that this de
termination cannot any wayes be taken from the primary cause
onely; but there is a necessity of introducing the secondary cau
ses, as namely the greater or lesse length of the Vessels, and
the greater or lesse depth of the waters in them conteined.
Which causes although they have not any operation in the moti
ons of the waters, those operations belonging to the sole prima
ry cause, without which no ebbing or flowing would happen,
yet neverthelesse they have a principal share in determining the
times or periods of the reciprocations, and herein their influ
ence is so powerful, that the primary cause must of force give
way unto them. The period of six hours therefore is no more
proper or natural than those of other intervals of times, though
indeed its the most observed, as agreeing with our Mediterrane,
which was the onely Sea that for many Ages was navigated:
though neither is that period observed in all its parts; for
that in some more angust places, such as are the Helle
spont, and the Ægean Sea, the periods are much shorter,
and also very divers amongst themselves; for which diver
sities, and their causes incomprehensible to Aristotle, some
say, that after he had a long time observed it upon some
cliffes of Negropont, being brought to desperation, he threw
himself into the adjoyning Euripus, and voluntarily drowned
himself.

The reason gi
ven, why the eb
bings and flowings,
for the most part,
are every six
hours.

In the third place we have the reason ready at hand, whence

it commeth to passe, that some Seas, although very long, as is
the Red Sea, are almost altogether exempt from Tides, which
happeneth because their length extendeth not from East to
West, but rather transversly from the Southeast to the North
west; but the motions of the Earth going from West to East;
the impulses of the water, by that means, alwayes happen to fall
in the Meridians, and do not move from parallel to parallel;
insomuch that in the Seas that extend themselves athwart to
wards the Poles, and that the contrary way are narrow, there is