Codex Madrid II

Codex II addresses different themes and can be divided into two clearly differentiated parts; the second of these is the booklet detailing the casting of Leonardo's Horse, which was added at an unknown date.

The first part (called Section A) takes the form of a notebook with layers of graphic elements, both verbal and representative. The content covers both personal and scientific fields indiscriminately.

The annotations were not made in order but at different times, even within the same page. Some pages give the impression of having been produced at the rhythm of the ideas flowing from da Vinci's mind.

The notebook includes some ethereal drawings of mountains in sanguine, created during a series of mapping operations in the Arno valley.

Likewise, this plan of Pisa, including the mouth of the river Arno, serves as a reminder that, in 1503, da Vinci was engrossed in one of his dreams: the project to divert the Arno and build a canal to connect Florence with the sea.

There are also drawings on architecture and military engineering, and others on geometry, especially regarding certain problems he was particularly intent on, such as squaring the circle. Others dealt with the flight of birds, the movement of waves, and musical instruments.

"Humans will never be able to reproduce the noise or buzzing generated when wings are flapped at speed by birds themselves, even if birds' wings were applied to a fast-moving instrument".

"On Saint Andrew's Day, I discovered the conclusion of squaring the circle; and it was completed as the candle waned, and night fell, and the paper I was writing on ran out, at the very end of the day."

The description of da Vinci's paper organ calls for a complete rethink of the composition of the elements of the barrel organ (organetto) as it existed at the time and had been constructed over various centuries. He made it lighter and added a continuous airstream via two vertical bellows placed side by side.

The second part (named Section B) is a monographic study. It is wholly dedicated to describing the technique of reproducing medals and plastic works in bronze.

"May 17, 1491, in the afternoon, here is a list of everything related to the project of the bronze horse on which I am currently working."

The nature of some of the themes covered (such as the project to divert the river Arno), confirm that da Vinci started to write Section A in the summer of 1503 and that the latest notes were not made after the middle of the year 1505.

On the other hand, the only two dates mentioned in Section B—May 17, 1491 and December 20, 1493—are related to the procedures devised by da Vinci to create the equestrian statue commissioned by Ludovico Sforza.