Castelli, Benedetto Of the mensuration of running waters 1661, tr. Salusbury
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37

OF THE
MENSURATION
OF
Running Waters.

SUPPOSITION I.

Let it be supposed, that the banks of the Rivers of which
we speak be erected perpendicular to the plane of the up­
per superficies of the River.

SUPPOSITION II.

We suppose that the plane of the bottome of the River, of
which we speak is at right angles with the banks.

SUPPOSITION III.

It is to be supposed, that we speak of Rivers, when they are at
ebbe, in that state of shallownesse, or at flowing in that state
of deepnesse, and not in their transition from the ebbe to the
flowing, or fr m the flowing to the ebbe.

Declaration of Termes.

FIRST.

If a River shall be cut by a Plane at right angles to the surface
of the water of the River, and to the banks of the River,
that same dividing Plane we call the Section of the River; and
this Section, by the Suppositions above, shall be a right angled
Parallelogram.

SECOND.

We call those Sections equally Swift, by which the water runs
with equal velocity; and more swift and less swift that
Section of another, by which the water runs with greater or lesse
velocity.