CONCERNING ARCHITRAVES OF ONE OR SEVERAL PIECES.

An architrave of several pieces is stronger than that of one single
piece, if those pieces are placed with their length in the direction
of the centre of the world. This is proved because stones have their
grain or fibre generated in the contrary direction i. e. in the
direction of the opposite horizons of the hemisphere, and this is
contrary to fibres of the plants which have ...

[Footnote: The text is incomplete in the original.]

_The Proportions of the stories of a building are indicated by a
sketch in MS. S. K. M. II2 11b (see Pl. LXXXV No. 15). The measures
are written on the left side, as follows: br 1 1/2--6 3/4--br
1/12--2 br--9 e 1/2--1 1/2--br 5--o 9--o 3 [br=braccia; o=oncie].

Pl. LXXXV No. 13 (MS. B. 62a) and Pl. XCIII No. 1. (MS. B. 15a) give
a few examples of arches supported on piers._

_XIII.

Theoretical writings on Architecture.

Leonardo's original writings on the theory of Architecture have come
down to us only in a fragmentary state; still, there seems to be no
doubt that he himself did not complete them. It would seem that
Leonardo entertained the idea of writing a large and connected book
on Architecture; and it is quite evident that the materials we
possess, which can be proved to have been written at different
periods, were noted down with a more or less definite aim and
purpose. They might all be collected under the one title: "Studies
on the Strength of Materials". Among them the investigations on the
subject of fissures in walls are particularly thorough, and very
fully reported; these passages are also especially interesting,
because Leonardo was certainly the first writer on architecture who
ever treated the subject at all. Here, as in all other cases
Leonardo carefully avoids all abstract argument. His data are not
derived from the principles of algebra, but from the laws of
mechanics, and his method throughout is strictly experimental.

Though the conclusions drawn from his investigations may not have
that precision which we are accustomed to find in Leonardo's
scientific labours, their interest is not lessened. They prove at
any rate his deep sagacity and wonderfully clear mind. No one
perhaps, who has studied these questions since Leonardo, has
combined with a scientific mind anything like the artistic delicacy
of perception which gives interest and lucidity to his observations.

I do not assert that the arrangement here adopted for the passages
in question is that originally intended by Leonardo; but their
distribution into five groups was suggested by the titles, or
headings, which Leonardo himself prefixed to most of these notes.
Some of the longer sections perhaps should not, to be in strict
agreement with this division, have been reproduced in their entirety
in the place where they occur. But the comparatively small amount of
the materials we possess will render them, even so, sufficiently
intelligible to the reader; it did not therefore seem necessary or
desirable to subdivide the passages merely for the sake of strict
classification._

_The small number of chapters given under the fifth class, treating
on the centre of gravity in roof-beams, bears no proportion to the
number of drawings and studies which refer to the same subject. Only
a small selection of these are reproduced in this work since the
majority have no explanatory text._

I.

ON FISSURES IN WALLS.