Now if we proceed to take to pieces the idea of architectural design,
and consider wherein the problem of it consists, we shall find that it
falls into a fourfold shape. It consists first in arranging the plan;
secondly, in carrying up the boundary lines of this plan vertically in
the shape of walls; thirdly, in the method of covering in the space
which we have thus defined and inclosed; and, fourthly, in the details
of ornamentation which give to it the last and concluding grace and
finish. All building, when it gets beyond the mere wall with which we
began, is really a method of covering in a space, or, if we may put it
so, a collection of spaces, marked out and arranged for certain
purposes. The first thing that the architect has to do is to arrange
these spaces on the ground so that they may conveniently meet the
necessary requirements of the building. Convenience and practical
usefulness come first; but in any building which is worth the name of
architecture something more than mere convenience has to be kept in
mind, even in the arrangement of the plan upon the site. It is to be a
combination of convenience with effectiveness of arrangement. We shall
probably find that some one compartment of the plan is of paramount
importance. We have to arrange the interior so that this most important
compartment shall be the climax of the plan.

The entrance and the other subsidiary compartments must be kept
subordinate to it, and must lead up to it in such a manner that the
spectator shall be led by a natural gradation from the subsidiary
compartments up to the main one, which is the center and _raison
d'etre_ of the whole--everything in the lines of the plan should point
to that. This is the great _crux_ in the planning of complicated public
buildings. A visitor to such a building, unacquainted with it
previously, ought to have no difficulty in finding out from the
disposition of the interior which are the main lines of route, and when