drawings if I took the opportunity of illustrating very briefly the
philosophy of elevations, plans, and sections, which many
non-professional people certainly do not understand.

[Illustration: Figs. 16 through 25]

A simple model of a building, like that in Fig. 16, will serve the
purpose, as the principle is the same in the most complicated as in the
simplest building. It must be remembered that the object of
architectural drawings on the geometrical system is not to show a
picture of the building, but to enable the designer to put together his
design accurately in all its parts, according to scale, and to convey
intelligible and precise information to those who have to erect the
building. A perspective drawing like Fig. 16 is of no use for this
purpose. It shows generally what the design is, but it is impossible to
ascertain the size of any part by scale from it, except that if the
length of one line were given it would be possible, by a long process of
projection and calculation, to ascertain the other sizes. The
_rationale_ of the architect's geometrical drawings is that on them each
plane of the building (the front, the side, the plan, etc.) is shown
separately and without any distortion by perspective, and in such a
manner that every portion is supposed to be opposite to the eye at once.
Only the width of any object on one side can be shown in this way at one
view; for the width of the return side you have to look to another
drawing; you must compare the drawings in order to find out those
relative proportions which the perspective view indicates to the eye at
a glance; but each portion of each side can be measured by reference to
a scale, and its precise size obtained, which can only be guessed at
roughly from the perspective drawing. Thus the side of the model is
shown in Fig. 19, the end in Fig. 17; the two together give the precise