nstrual_ motion the Center moves in the Circle L T N; each
point in its surface, by its diurnal motion moves in the Circle L M N:
whatever effect (accelerative or tardative) the _Menstrual_ would give,
that effect by the _Diurnal_ is increased in the parts L M N (or rather l M
n. the Semicircle) and most of all at M: but diminished in the parts N O L
(or rather n O l) and most of all at O. So that at M, and O, (that is when
the Moon is in the _Meridian_ below or above the _Horizon_,) we are to have
the Diurnal Tide or High-water, occasioned by the greatest Acceleration or
Retardation, which the _Diurnal_ Arch gives to that of the _Menstrual_:
which seems to be the true cause of the _Daily Tides_. And withall gives an
account, not onely why it should be _every_ day; but like wise, why at
_such a time_ of the day; and why this time should in a moneth run through
the whole 24 hours; _viz._ because the Moons coming to the _Meridian_ above
and below the _Horizon_, (or as the Seamen call it, the _Moons Southing_,
and _Northing_,) doth so: As likewise of the _Spring tides_ and
_Neap-tides_. For, when it so happens, that the _Menstrual_ and _Diurnal_
Accelerations or Retardations, be coincident, (as at New moons and
Full-moons they are,) the effect must needs be the greater. And although
(which is not to be dissembled) this happen {275} but to one of the two
Tides; that is, the Night-tide at the New-moon (when both motions do most
of all Accelerate,) and the Day-tide at Full-moon (when both do most Retard
the _Annual_ motion;) Yet, this tide being thus raised by two concurrent
causes; though the next Tide have not the same cause also, the _Impetus_
contracted will have influence upon the next Tide; Upon a like reason, as a
_Pendulum_ let fall from a higher Arch, will (though there be no new cause
to occasion it) make the Vibration on the other side (beyond the
Perpendicular) to be also greater: Or, of water in a broad Vessel, if it be
so jogged, as to be cast forward to a good height above its Levell, will
upon its recoyling, by its own gravity, (without any additional cause)
mount so much the higher on the hinder part.

But here also we are to take notice, that though all parts of the Earth by
its _Diurnal_ motion do turn about its Axis, and describe _parallel_
Circles; yet not _equal_ Circles; but _greater_ neer the _AEquinoctial_, and
_lesser_ near the _Poles_, which may be a cause why the Tides in some parts
may be much great