The shaded afterlife of Leonardo’s notebooks – ‘without parallel in theintellectual history of word and image’, as Kemp describes them – stands insharp relief when we light it with the long, powerful burn of Pacioli’sposthumous – albeit near-anonymous – career. There’s no doubt thatLeonardo was the greater thinker, but his creative achievements madescarcely any impression compared to the impact of the universal adoptionof his friend’s Summa.

up Isabella d’Este’s portrait, complaining of Leonardo’s ‘haphazard andextremely unpredictable’ routine. This frustrating restlessness was, ofcourse, integral to the obsessive creativity. Pacioli had been able to draw aline under a piece of work and consider it done, but for Leonardo thisrepresented a mental hurdle that he frequently failed to clear. He leftpaintings unfinished for decades – Lisa del Giocondo sat for the Mona Lisawhen she was in her early twenties, and was thirty-nine when Leonardodied, still working on it – and he evidently felt similarly about hismanuscripts and notebooks

Melzi’s posthumousedition of the Treatise on Painting, for instance, would require collationfrom no fewer than eighteen notebooks.

Why did Leonardo not go to Venice to publish when Pacioli did? Had hetidied up the texts in his notebooks, he would have had no difficulty findinga patron and printer, and could have seen several books into print at thesame time as his friend.

Pacioli completed another equally playful book at about the same time:De Viribus Quantitatis (‘On the powers of numbers’), which compilesnumber games, card tricks, riddles and reasoning problems. It makesfrequent mention of Leonardo, and much of the content overlaps withpuzzles that can be found in the notebooks.

‘Alas, this will never get anything done’ is a theme that recurs in severalnotebooks.

In February 1498, Maestro Lucacompleted De Divina Proportione, which was illustrated by ‘the graciousleft hand’ of his new friend, as Leonardo showed off his mastery ofperspective and geometry with a set of precise, fenestrated illustrations ofthe six Platonic solids, from the four-faced tetrahedron to the twenty-sidedicosahedron.

This habit of drawing engaged one of his most important analyticaltools: analogy. Drawing from nature in detail forces the artist to understandboth underlying structure and surface detail, and this close examination ledLeonardo to make surprising connections, noting the resemblances betweenthe curls of hair and the movement of water, a sprouting seed and thevessels around the human heart, ropes and levers and tendons and bones.These connections would prove distracting – ‘lateral thinking at apathological level’, as Kemp puts it – but the result was that ‘he couldalways see further possibilities’.

He analysed the flow of blood around the heart, makingthe world’s first post-mortem diagnosis of arteriosclerosis, and worked outhow the aortic valve manages the turbulence of rushing blood.

Over six thousand leaves (which is tosay, thirteen thousand pages) survive, and experts estimate that thisrepresents about a quarter of the original total. This implies that Leonardofilled his notebooks at the rate of about a thousand pages a year, allobsessively covered with drawings, diagrams and idiosyncratic mirrorhandwriting. ‘I worked out at one point that he must have written aboutfifty academic-length books, if you put them all together,’ says Kemp. ‘Hewas never at rest.’

The successful artist towhom he was apprenticed in Florence, Andrea del Verrocchio, ran a book-making workshop out of his house on Via Ghibellina, just off the street ofbookshops, where the cartolai clustered

Pacioli’s reader, in whose company he would spend most of thefollowing decade, was Leonardo da Vinci.

As you go about town…constantly observe, note, and consider the circumstances and behavior of men as they talk, quarrel, or laugh, or come to blows. — Codex Ash.

Despite the crudeness of his experimental setup 500 years ago, da Vinci, Dr. Gharib said, was able to calculate the gravitational constant to an accuracy within 10 percent of the modern value.

The Codex Arundel, named after a British collector, the Earl of Arundel, who acquired it early in the 17th century. Da Vinci composed the collection of hundreds of papers between 1478 and 1518 — that is, between the ages of 26 and 66 — the year before his death. The papers now reside in the British Library. The collection features his famous mirror-writing as well as diagrams, drawings and texts covering a range of topics in art and science.

The creation of L.H.O.O.Q. profoundly transformed the perception of La Joconde (what the French call the painting, in contrast with the Americans and Germans, who call it the Mona Lisa).

But crucially, he believes the pool at the center of the complex may have also served as a surface to observe and map the stars. The water surface would have mirrored the sky, as water does – none other than Leonardo da Vinci pointed out the attributes of inert standing water when studying the night sky. For one thing, the stars were adored by the Phoenicians, whether as gods or deceased ancestors; and the position of the constellations was of keen interest to the sailors among them for navigation purposes, Nigro points out.