Leonardo’s scientific and technical observations are found in his handwritten notes and drawings, of which about 7,200 pages survive of approximately 25,000. Most of these are bound into ‘codices’ (ancient manuscripts in book form). These notebooks have been rightly referred to as ‘the most astonishing testament to the powers of human observation and imagination ever set down on paper.’
Leonardo rarely put dates on his pages and much of the order has been lost. After his death, many of the volumes were disassembled and the more interesting pages sold or reorganised in the late 16th century by Pompeo Leoni, a sculptor in the court of the King of Spain, who came into possession of many of the remaining pages. He tried to organise them by subject – an admirable endeavour, but one that ultimately only resulted in disturbing the original order of the pages, which may have been key to our understanding of Leonardo’s thought processes. Each of the new books created by this process is now known as a codex.
Codex Arundel:
This collection, comprising a paper manuscript bound in Morocco leather, is housed in the British Library in London. It contains 238 pages of varying sizes that have been cut and removed from other manuscripts. The notes deal with a variety of subjects, including geometry, weights and architecture.
Codex Forster (1–3):
These three parchment-bound paper manuscripts are housed in London at the Victoria and Albert Museum. The manuscripts are known as Forster 1 (two parts, one completed from 1487–1490 and one in 1505), Forster 2 (1495–1497) and Forster 3 (1490–1496). They include studies on geometry, weights and hydraulic machines.
Codex Atlanticus:
This Codex, kept in the Biblioteca Ambrosiana in Milan, encompasses Leonardo’s entire career, from 1478 to 1519. Today it consists of twelve leather-bound volumes, comprising 1,119 pages of different sizes. Various themes are touched on, including mathematics, geometry, astronomy, botany, zoology and the military arts. The name ‘Codex Atlanticus’ derives from the original arrangement of all the sheets in a single large-sized volume, akin to an atlas. Codex Atlanticus was created around the end of the sixteenth century when sculptor Pompeo Leoni dismembered the original Leonardo manuscripts, separating the scientific and technical drawings of Codex Atlanticus from the naturalistic and anatomical ones that are today scattered among the other codices, most notably the Royal Windsor collection.
Codex Leicester:
This leather-bound paper manuscript was purchased by Bill Gates in 1994 for U.S. $30.8 Million (A.U.D. $46.7 million). It comprises 64 sheets, dedicated primarily to studies in hydraulics and the movement of water but also including studies in geology and astronomy. The manuscripts can be dated from 1504 to 1506.
Codex Trivulzianus:
This codex, held in the Biblioteca Trivulziana at the Castello Sforzesco in Milan, contains studies in architecture and religious themes, as well as numerous pages testifying to Leonardo’s efforts to improve his literary education. Unfortunately only 55 of the original 62 pages remain, mostly dating from 1487 to 1490.
Windsor Folios:
Held in Windsor Castle’s Royal Collection, these folios comprise approximately 234 unbound sheets containing nearly 600 drawings of various sizes, composed between 1478 and 1518. The subjects of the drawings include anatomy, geography, cartography, horse studies and even caricatures.
Codex ‘On the Flight of Birds:'
Held in the Biblioteca Reale of Turin, this collection includes 17 of the 18 original pages in which Leonardo methodically analyses the flight of birds, paying close attention to the mechanics of flight as well as air resistance, winds and currents. The pages can be dated from approximately 1505.
Codex Ashburnham:
These two cardboard-bound manuscripts, held in the Institut de France, Paris, consist of pages stolen from codices A and B in the 19th century and eventually sold to Lord Ashburnham. The collections mainly contain pictorial studies and assorted drawings which Leonardo is believed to have drawn between 1489 and 1492.
Codices of the Institut de France:
The codices held at the Institut de France, Paris, comprise 12 paper manu-scripts labelled A to M, variably bound in parchment, leather and cardboard. They vary widely in size, from approximately A7 (Codex M, 10 x 7 cm) to A4 (Codex C, 31 x 22 cm). A range of subjects are covered, including military art, optics, geometry, the flight of birds and hydraulics. The majority of the pages are thought to date from 1492 to 1516.
The Madrid Codices:
These two manuscripts were discovered in the National Library of Madrid in 1966, bound in red Morocco leather, after having lain hidden for years. To facilitate easy identification, they were named Madrid I and Madrid II. Madrid I consists of 192 sheets penned between 1490 and 1496, most of which focus on mechanics. Madrid II is primarily dedicated to studies in geometry and dates from 1503 to 1505.