out in the labours of others will not allow me my own.  They will say that I, having no literary skill, cannot properly express that which I desire to treat of [Footnote 26:  le mie cose .... che d’altra parola.  This can hardly be reconciled with Mons. RAVAISSON’S estimate of L. da Vinci’s learning. “Leonard de Vinci etait un admirateur et un disciple des anciens, aussi bien dans l’art que dans la science et il tenait a passer pour tel meme aux yeux de la posterite.” Gaz. des Beaux arts.  Oct. 1877.]; but they do not know that my subjects are to be dealt with by experience rather than by words [Footnote 28:  See Footnote 26]; and [experience] has been the mistress of those who wrote well.  And so, as mistress, I will cite her in all cases.

11.

Though I may not, like them, be able to quote other authors, I shall rely on that which is much greater and more worthy:—­on experience, the mistress of their Masters.  They go about puffed up and pompous, dressed and decorated with [the fruits], not of their own labours, but of those of others.  And they will not allow me my own.  They will scorn me as an inventor; but how much more might they—­who are not inventors but vaunters and declaimers of the works of others—­be blamed.

INTRODUCTION.

And those men who are inventors and interpreters between Nature and Man, as compared with boasters and declaimers of the works of others, must be regarded and not otherwise esteemed than as the object in front of a mirror, when compared with its image seen in the mirror.  For the first is something in itself, and the other nothingness.—­Folks little indebted to Nature, since it is only by chance that they wear the human form and without it I might class them with the herds of beasts.

12.

Many will think they may reasonably blame me by alleging that my proofs are opposed to the authority of certain men held in the highest reverence by their inexperienced judgments; not considering that my works are the issue of pure and simple experience, who is the one true mistress.  These rules are sufficient to enable you to know the true from the false—­and this aids men to look only for things that are possible and with due moderation—­and not to wrap yourself in ignorance, a thing which can have no good result, so that in despair you would give yourself up to melancholy.

13.

Among all the studies of natural causes and reasons Light chiefly delights the beholder; and among the great features of Mathematics the certainty of its demonstrations is what preeminently (tends to) elevate the mind of the investigator.  Perspective, therefore, must be preferred to all the discourses and systems of human learning.  In this branch [of science] the beam of light is explained on those methods of demonstration which form the glory not so much of Mathematics as of Physics and are graced with the flowers of both [Footnote:  5.  Such of Leonardo’s