The Elements of Hydrostatics

Water staining on the left edge of the page; ink blot on the upper right.

POSTULATES.

I. POSTULATE.

THE weight of bodies in the air is called their own, but in water according to their nature.

II. POSTULATE.

THE proposed water is to be of uniform weight everywhere.

III. POSTULATE.

THE weight that causes a vessel to sink shallower is lighter, but deeper is heavier, and at the same depth is of equal weight.

IV. POSTULATE.

THE surface vessel can hold water and other matter without breaking or changing its form.

V. POSTULATE.

THE surface vessel, once the water is poured out, remains empty.

To remain empty, that is not void, for otherwise the weight of the air would be lacking.

To be a plane parallel to the Horizon.

VI. POSTULATE.

EVERY surface of water is a *plane, parallel to the horizon.

Which, in view of the fact that it is part of the spherical surface or world-surface (we call a world-surface any spherical surface whose center is the center of the world), also in a drop lying or hanging anywhere, or in water where a body might be coated, is not so; but in such a small quantity of water as this, nor in as large a one where that is perceptible, do not alter the following * propositions.