p-heavy; but the entasis
is an additional optical correction to prevent their outline from
appearing hollowed, which it would have done had there been no curve.
The columns of the Parthenon have shafts that are over 34 ft. high,
and diminish from a diameter of 6.15 ft. at the bottom to 4.81 ft. at
the top. The outline between these points is convex, but so slightly
so that the curve departs at the point of greatest curvature not more
than 3/4 in. from the straight line joining the top and bottom. This
is, however, just sufficient to correct the tendency to look hollow in
the middle.

A second correction is intended to overcome the apparent tendency of a
building to spread outwards towards the top. This is met by inclining
the columns slightly inwards. So slight, however, is the inclination,
that were the axes of two columns on opposite sides of the Parthenon
continued upwards till they met, the meeting-point would be 1952
yards, or, in other words, more than one mile from the ground.

Another optical correction is applied to the horizontal lines. In
order to overcome a tendency which exists in all long lines to seem as
though they droop in the middle, the lines of the architrave, of the
top step, and of other horizontal features of the building, are all
slightly curved. The difference between the outline of the top step of
the Parthenon and a straight line joining its two ends is at the
greatest only just over 2 inches.

The last correction which it is necessary to name here was applied to
the vertical proportions of the building. The principles upon which
this correction rests have been demonstrated by Mr. John
Pennethorne;[14] and it would hardly come within the scope of this
volume to attempt to state them here: suffice it to say, that small
additions, amounting in the entire height of the order to less than 5
inches, were made to the heights of the various members of the order,
with a view to secure that from one definite point of view the effect
of foreshortening should be exactly compensated, and so the building
should appear to the spectator to be perfectly proportioned.

The Parthenon, like many, if not all Greek buildings, was profusely
decorated with coloured ornaments, of which nearly every trace has now
disappeared, but which must have contributed largely to the splendid
beauty of the building as a whole, and must have emphasised and set
off its parts. The ornaments known as Doric frets were largely
emp