oportions required. For round arches the height may
be twice that of the base, varying to one and a half. In Gothic arches
the height may be about three times the width, all of which proportions
are chosen to suit the different purposes and effects required. Divide
the base _AB_ into the desired number of parts, 8, 10, 12, &c., each
part representing 1 foot. (In this case the base is 10 feet and the
horizon 5 feet.) Set out floor by means of 1/4 distance. Divide it into
squares of 1 foot, so that there will be 8 feet between each column or
pilaster, supposing we make them to stand on a square foot. Draw the
first archway _EKF_ facing us, and its inner semicircle _gh_, with also
its thickness or depth of 1 foot. Draw the span of the archway _EF_,
then central line _PO_ to point of sight. Proceed to raise as many other
arches as required at the given distances. The intersections of the
central line with the chords _mn_, &c., will give the centres from which
to describe the semicircles.

CXXVII

OUTLINE OF AN ARCADE WITH SEMICIRCULAR ARCHES

This is to show the method of drawing a long passage, corridor, or
cloister with arches and columns at equal distances, and is worked in
the same way as the previous figure, using 1/4 distance and 1/4 base.
The floor consists of five squares; the semicircles of the arches are
described from the numbered points on the central line _OS_, where it
intersects the chords of the arches.

[Illustration: Fig. 233.]

CXXVIII

SEMICIRCULAR ARCHES ON A RETREATING PLANE

First draw perspective square _abcd_. Let _ae'_ be the height of the
figure. Draw _ae'f'b_ and proceed with the rest of the outline. To draw
the arches begin with the one facing us, _Eo'F_ enclosed in the
quadrangle _Ee'f'F_. With centre _O_ describe the semicircle and across
it draw the diagonals _e'F_, _Ef'_, and through _nn_, where these lines
intersect the semicircle, draw horizontal _KK_ and also _KS_ to point of
sight. It will be seen that the half-squares at the side are the same
size in perspective as the one facing us, and we carry out in them much
the same operation; that is, we draw the diagonals, find the point _O_,
and the points _nn_, &c., through which to draw our arches. See
perspective of the circle (Fig. 165).

[Illustration: Fig. 234.]

If more points are required an additional diagonal from _O_ to _K_ may
be used, as shown in the figure, which perhaps explains itself. The
method