5.

Of digging a canal.  Put this in the Book of useful inventions and in proving them bring forward the propositions already proved.  And this is the proper order; since if you wished to show the usefulness of any plan you would be obliged again to devise new machines to prove its utility and thus would confuse the order of the forty Books and also the order of the diagrams; that is to say you would have to mix up practice with theory, which would produce a confused and incoherent work.

6.

I am not to blame for putting forward, in the course of my work on science, any general rule derived from a previous conclusion.

7.

The Book of the science of Mechanics must precede the Book of useful inventions.—­Have your books on anatomy bound! [Footnote:  4.  The numerous notes on anatomy written on loose leaves and now in the Royal collection at Windsor can best be classified in four Books, corresponding to the different character and size of the paper.  When Leonardo speaks of ‘li tua libri di notomia’, he probably means the MSS. which still exist; if this hypothesis is correct the present condition of these leaves might seem to prove that he only carried out his purpose with one of the Books on anatomy.  A borrowed book on Anatomy is mentioned in F.O.]

8.

The order of your book must proceed on this plan:  first simple beams, then (those) supported from below, then suspended in part, then wholly [suspended].  Then beams as supporting other weights [Footnote:  4.  Leonardo’s notes on Mechanics are extraordinarily numerous; but, for the reasons assigned in my introduction, they have not been included in the present work.].

General introductions to the book on Painting (9-13).

9.

INTRODUCTION.

Seeing that I can find no subject specially useful or pleasing—­since the men who have come before me have taken for their own every useful or necessary theme—­I must do like one who, being poor, comes last to the fair, and can find no other way of providing himself than by taking all the things already seen by other buyers, and not taken but refused by reason of their lesser value.  I, then, will load my humble pack with this despised and rejected merchandise, the refuse of so many buyers; and will go about to distribute it, not indeed in great cities, but in the poorer towns, taking such a price as the wares I offer may be worth. [Footnote:  It need hardly be pointed out that there is in this ‘Proemio’ a covert irony.  In the second and third prefaces, Leonardo characterises his rivals and opponents more closely.  His protest is directed against Neo-latinism as professed by most of the humanists of his time; its futility is now no longer questioned.]

10.

INTRODUCTION.