The Elements of Hydrostatics

VIII DEFINITION.

BASE is any surface against which any water rests.

IX DEFINITION.

Planum. Centrum. Plane. Center.

We call a REGULAR base any surface that is divided into two equal parts by every straight line passing through its center.

EXPLANATION.

Such as circles, ellipses, parallelograms, and all regular polygons inscribable in a circle whose number of sides is even, and all others of whatever form they might be, such as A, B, and the like, which can be divided into two equal parts by every straight line through their center, we call Regular bases, in contrast to those that cannot be divided into two equal parts by every straight line through their center, which, by the inversion of this definition, are called irregular bases, such as triangles, and polygons with an odd number of sides, and the like.

A geometric diagram shows two figures labeled A and B. Figure A is a symmetrical, eight-pointed star-like shape. Figure B is a four-lobed flower or quatrefoil shape. Both illustrate the concept of "regular bases" that can be divided into two equal parts by any straight line passing through their center.

The reason for the definition of this Regular base is (as will appear in the following) that a pillar whose base is a regular base is divided into two equal parts by every plane through two Homologa. Corresponding points. *corresponding points standing directly opposite each other in the perimeters of the base and the top.

X DEFINITION.

We call VOID a place where no body exists.

XI DEFINITION.

EMPTY is where there is nothing but air.