The dangers of a lot of knowledge

By chance, I received a copy of Martin Kemp's new book about Leonardo da Vinci shortly after reading Charles Nicholl's recently published popular biography. Slightly to my surprise, I had greatly admired Nicholl's book - a vigorous, independently researched and lively account of all aspects of Leonardo's life, from his childhood to his sex life, travels and shopping. Nicholl provides an ideal introduction to Leonardo's art, science and milieu.

Kemp's book, published after a lifetime of research on the artist, might be expected to do something broadly comparable. In fact, it is clear from the book's introduction that it was commissioned by its publisher, Oxford University Press, as one of a series of so-called Very Short Introductions. Its intention is clearly to provide an analytical insight into the nature of Leonardo's life and mind through a series of loosely related essays on different aspects of his interests - for example, how the eye absorbs information into the cortex of the brain and the way the body is constructed.

However, while Kemp's book is promoted as if it might be read as an introduction to the life of Leonardo for a non-specialist, without previous knowledge of his art, in practice it reads more like an advanced postgraduate research seminar.

The reader is presumed to be familiar with the chronology of Leonardo's life and the first chapter is an extremely partial account of only some aspects of it, including his finances. There is a fuller and more useful outline of key dates at the back, as well as a list of his paintings.

In fact, I suspect that Kemp knows too much about Leonardo to be able easily to distil it into a short book and has found it quite tricky to decide which topics to write about. The depth of his knowledge is evident throughout the text. Indeed, he probably knows more than almost anyone else living, except possibly Carlo Pedretti, about Leonardo's ideas, having studied them with great intensity throughout his career. His insights are doubtless strengthened by his training as a scientist before becoming an academic art historian.

The author conveys a passionate interest in what Leonardo had in common with his contemporaries, including most of the outward aspects of his life, which Kemp is inclined to treat as less abnormal than many of Leonardo's previous biographers. This is contrasted with the exceptional individuality of Leonardo's intellectual interests and the ways in which he developed these interests through the outpouring of notes, drawings and annotations in his great series of Notebooks , which Kemp regards as infinitely more important and absorbing in terms of the history of culture than the relatively small number of Leonardo's surviving paintings.

Indeed, one of the book's oddities is that it is only in the last chapter that Kemp finally begins to engage with Leonardo's art, which is what most people are likely to want to read about. Up to this point, we see, in reproduction, some of Leonardo's more extraordinary drawings - for example, the cross-section of a skull in the Royal Library, Windsor. We cannot help but marvel at Leonardo's wonderful combination of analytical geometry and imaginative interpretation, converting bones into a magical piece of three-dimensional realism. But we are not told much about this drawing beyond the fact that it depicts the medieval system of "faculty psychology".

It is only towards the end of the book that Kemp discusses the Mona Lisa . Here, one discovers the full force of his interpretative powers, his ability to relate the specific character and qualities of the image to what he knows of the history of Lisa Gherardini and to what he rightly regards as a revolution in portraiture, which, for the first time, is able to depict character rather than simply external appearance.

This is a distinction which Leonardo himself recognised when he wrote: "The good painter has to paint two principal things, that is to say man and the intention of his mind. The first is easy and the second is difficult, because the latter has to be recognised through gesture and movements of the limbs."

Kemp returns to the Mona Lisa in his final chapter, when he reminds us that he wrote the book in the Villa Vignamaggio, where Gherardini lived.

Disarmingly, he has already revealed in his introduction that he wrote the book in ten days. I can see the point of this. Leonardo is, after all, an attempt to provide a succinct summary account of a lifetime of research.

But this approach has disadvantages as well, including a certain amount of postmodern self-indulgence, a lack of a clear and consistent structure to the book, not enough basic information, and some slipshod editing unworthy of a university press, including the mis-spelling of "mathematical" as "mathermatical".

Charles Saumarez Smith is director, National Gallery.