[Footnote: The figure on Pl. CV, No. 4 belongs to the first
paragraph of this passage, lines 1-14; fig. 5 is sketched by the
side of lines l5--and following. The sketch below of a pomegranate
refers to line 22. The drawing fig. 6 is, in the original, over line
37 and fig. 7 over line 54.]

Which of these two cubes will shrink the more uniformly: the cube
_A_ resting on the pavement, or the cube _b_ suspended in the air,
when both cubes are equal in weight and bulk, and of clay mixed with
equal quantities of water?

The cube placed on the pavement diminishes more in height than in
breadth, which the cube above, hanging in the air, cannot do. Thus
it is proved. The cube shown above is better shown here below.

The final result of the two cylinders of damp clay that is _a_ and
_b_ will be the pyramidal figures below _c_ and _d_. This is proved
thus: The cylinder _a_ resting on block of stone being made of clay
mixed with a great deal of water will sink by its weight, which
presses on its base, and in proportion as it settles and spreads all
the parts will be somewhat nearer to the base because that is
charged with the whole weight.

III.

ON THE NATURE OF THE ARCH.

779.

WHAT IS AN ARCH?