Salusbury, Thomas Mathematical collections and translations 1667

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391
on other different concomitant causes, although they ought all
to have connexion with the primary; therefore it is convenient
that we propound and examine the several accidents that may
be the causes of such different effects.

Demonstrations
how the parts of
the terrestriall
Globe accelerats
and ratard.

The parts of a
Circle regularly
moved about its
own centre move in
divers times with
contrary motions.

The mixture of
the two motions
annnal and diur­
nal, causeth the
inequality in the
motion of the parts
of the terrestrial
Globe.

The most potent
and primary cause
of the ebbing and
flowing.

The first of which is, that when ever the water, by means of a

notable retardation or acceleration of the motion of the Vessel,
its container, shall have acquired a cause of running towards this

or that extream, and shall be raised in the one, and abated in the

other, it shall not neverthelesse continue, for any time in that
state, when once the primary cause is ceased: but by vertue of
its own gravity and natural inclination to level and grow, even it
shall speedily return backwards of its own accord, and, as being
grave and fluid, shall not only move towards Æquilibrium; but
being impelled by its own impetus, shall go beyond it, rising in
the part, where before it was lowest; nor shall it stay here, but
returning backwards anew, with more reiterated reciprocations of
its undulations, it shall give us to know, that it will not from a
velocity of motion, once conceived, reduce it self, in an instant,
to the privation thereof, and to the state of rest, but will succes­
sively, by decreasing a little and a little, reduce it self unto the
same, just in the same manner as we see a weight hanging at a
cord, after it hath been once removed from its state of rest, that
is, from its perpendicularity, of its own accord, to return thither
and settle it self, but not till such time as it shall have often
past to one side, and to the other, with its reciprocall vi­
brations.

Sundry accidents
that happen in the
ebbings & flowings

The first acci­
dent.

The Water rai­
sed in one end of
the Vessel return­
eth of its self to
Æquilibrium.

The second accident to be observed is, that the before­

declared reciprocations of motion come to be made and repeated
with greater or lesser frequency, that is, under shorter or longer
times, according to the different lengths of the Vessels contain­
ing the waters; so that in the shorter spaces the reciprocati­
ons are more frequent, and in the longer more rare: just as in
the former example of pendent bodies, the vibrations of those
that are hanged to longer cords are seen to be lesse frequent,
than those of them that hang at shorter strings.

In the shorter
Vissels the undula­
tions of waters are
more frequent.

And here, for a third observation, it is to be noted, that not

onely the greater or lesser length of the Vessel is a cause that
the water maketh its reciprocations under different times; but
the greater or lesser profundity worketh the same effect. And
it happeneth, that of waters contained in receptacles of equall
length, but of unequal depth, that which shall be the deepest,
maketh its undulations under shorter times, and the reciprocati­
ons of the shallower waters are lesse frequent.

The greater
profundity maketh
the undulations of
waters more fre­
quent.

Fourthly, there are two effects worthy to be noted, and di­
ligently observed, which the water worketh in those its vibra­