by Leonardo da Vinci
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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.
Schemes for the arrangement of the materials (919-928).
919.
These books contain in the beginning: Of the nature of water itself in its motions; the others treat of the effects of its currents, which change the world in its centre and its shape.
920.
921.
First you shall make a book treating of places occupied by fresh waters, and the second by salt waters, and the third, how by the disappearance of these, our parts of the world were made lighter and in consequence more remote from the centre of the world.
922.
First write of all water, in each of its motions; then describe all its bottoms and their various materials, always referring to the propositions concerning the said waters; and let the order be good, for otherwise the work will be confused.
Describe all the forms taken by water from its greatest to its smallest wave, and their causes.
923.
924.
Place at the beginning what a river can effect.
925.
A book of driving back armies by the force of a flood made by releasing waters.
A book showing how the waters safely bring down timber cut in the mountains.
A book of boats driven against the impetus of rivers.
A book of raising large bridges higher. Simply by the swelling of the waters.
A book of guarding against the impetus of rivers so that towns may not be damaged by them.
926.
A book of the ordering of rivers so as to preserve their banks.
A book of the mountains, which would stand forth and become land, if our hemisphere were to be uncovered by the water.
A book of the earth carried down by the waters to fill up the great abyss of the seas.
A book of the ways in which a tempest may of itself clear out filled up sea-ports.
A book of the shores of rivers and of their permanency.
A book of how to deal with rivers, so that they may keep their bottom scoured by their own flow near the cities they pass.
A book of how to make or to repair the foundations for bridges over the rivers.
A book of the repairs which ought to be made in walls and banks of rivers where the water strikes them.
A book of the formation of hills of sand or gravel at great depths in water.
927.
