Let no man who is not a Mathematician read the elements of my work. The disorder in the MSS. 4. Begun at Florence, in the house of Piero di Braccio Martelli, on the 22nd day of March 1508. And this is to be a collection without order, taken from many papers which I have copied here, hoping to arrange them later each in its place, according to the subjects of which they may treat. But I believe that before I am at the end of this [task] I shall have to repeat the same things several times; for which, O reader! do not blame me, for the subjects are many and memory cannot retain them [all] and say: 'I will not write this because I wrote it before.' And if I wished to avoid falling into this fault, it would be necessary in every case when I wanted to copy [a passage] that, not to repeat myself, I should read over all that had gone before; and all the more since the intervals are long between one time of writing and the next. [Footnote: 1. In the history of Florence in the early part of the XVIth century _Piero di Braccio Martelli_ is frequently mentioned as _Commissario della Signoria_. He was famous for his learning and at his death left four books on Mathematics ready for the press; comp. LITTA, _Famiglie celebri Italiane_, _Famiglia Martelli di Firenze_.--In the Official Catalogue of MSS. in the Brit. Mus., New Series Vol. I., where this passage is printed, _Barto_ has been wrongly given for Braccio. 2. _addi 22 di marzo 1508_. The Christian era was computed in Florence at that time from the Incarnation (Lady day, March 25th). Hence this should be 1509 by our reckoning. 3. _racolto tratto di molte carte le quali io ho qui copiate_. We must suppose that Leonardo means that he has copied out his own MSS. and not those of others. The first thirteen leaves of the MS. in the Brit. Mus. are a fair copy of some notes on physics.] Suggestions for the arrangement of MSS treating of particular subjects.(5-8). 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.