Divide an hour into 3000 parts, and this you can do with a clock by
making the pendulum lighter or heavier.

_XVI.

Physical Geography.

Leonardo's researches as to the structure of the earth and sea were
made at a time, when the extended voyages of the Spaniards and
Portuguese had also excited a special interest in geographical
questions in Italy, and particularly in Tuscany. Still, it need
scarcely surprise us to find that in deeper questions, as to the
structure of the globe, the primitive state of the earth's surface,
and the like, he was far in advance of his time.

The number of passages which treat of such matters is relatively
considerable; like almost all Leonardo's scientific notes they deal
partly with theoretical and partly with practical questions. Some of
his theoretical views of the motion of water were collected in a
copied manuscript volume by an early transcriber, but without any
acknowledgment of the source whence they were derived. This copy is
now in the Library of the Barberini palace at Rome and was published
under the title: "De moto e misura dell'acqua," by FRANCESCO
CARDINALI, Bologna_ 1828. _In this work the texts are arranged under
the following titles:_ Libr. I. Della spera dell'acqua; Libr. II.
Del moto dell'acqua; Libr. III. Dell'onda dell'acqua; Libr. IV. Dei
retrosi d'acqua; Libr. V. Dell'acqua cadente; Libr. VI. Delle
rotture fatte dall'acqua; Libr. VII Delle cose portate dall'acqua;
Libr. VIII. Dell'oncia dell'acqua e delle canne; Libr. IX. De molini
e d'altri ordigni d'acqua.

_The large number of isolated observations scattered through the
manuscripts, accounts for our so frequently finding notes of new
schemes for the arrangement of those relating to water and its
motions, particularly in the Codex Atlanticus: I have printed
several of these plans as an introduction to the Physical Geography,
and I have actually arranged the texts in accordance with the clue
afforded by one of them which is undoubtedly one of the latest notes
referring to the subject (No._ 920_). The text given as No._ 930
_which is also taken from a late note-book of Leonardo's, served as
a basis for the arrangement of the first of the seven books--or
sections--, bearing the title: Of the Nature of Water_ (Dell'acque
in se).

_As I have not made it any part of this undertaking to print the
passages which refer to purely physical principles, it has also been
necessary to exclude those practical researches which, in accordance
with indications given in_ 920, _ought to come in as Books_ 13, 14
_and_ 15. _I can only incidentally mention here that Leonardo--as it
seems to me, especially in his youth--devoted a great deal of
attention to the construction of mills. This is proved by a number
of drawings of very careful and minute execution, which are to be
found in the Codex Atlanticus. Nor was it possible to include his
considerations on the regulation of rivers, the making of canals and
so forth (No._ 920, _Books_ 10, 11 _and_ 12_); but those passages in
which the structure of a canal is directly connected with notices of
particular places will be found duly inserted under section XVII
(Topographical notes). In Vol. I, No._ 5 _the text refers to
canal-making in general._

_On one point only can the collection of passages included under the
general heading of Physical Geography claim to be complete. When
comparing and sorting the materials for this work I took particular
care not to exclude or omit any text in which a geographical name
was mentioned even incidentally, since in all such researches the
chief interest, as it appeared to me, attached to the question
whether these acute observations on the various local
characteristics of mountains, rivers or seas, had been made by
Leonardo himself, and on the spot. It is self-evident that the few
general and somewhat superficial observations on the Rhine and the
Danube, on England and Flanders, must have been obtained from maps
or from some informants, and in the case of Flanders Leonardo
himself acknowledges this (see No._ 1008_). But that most of the
other and more exact observations were made, on the spot, by
Leonardo himself, may be safely assumed from their method and the
style in which he writes of them; and we should bear it in mind that
in all investigations, of whatever kind, experience is always spoken
of as the only basis on which he relies. Incidentally, as in No._
984, _he thinks it necessary to allude to the total absence of all
recorded observations._

I.

INTRODUCTION.

Schemes for the arrangement of the materials (919-928).