Da Vinci is most famous now for his inventions: his bicycle, airplane, helicopter, and parachute were all some 500 years ahead of their time. However, he also showed remarkable insight in the world of science. The only remains of this work are his notebooks, now among the most valuable documents in the world. The thousands of surviving pages reveal the most eclectic of minds. He wrote and drew about subjects including geology, anatomy, flight, gravity and optics, often flitting from subject to subject on a single page in his left-handed mirror script. His writings are widely regarded as preliminary stages of works destined for publication, but never completed.

In fact, the only surviving examples of work that he both executed and finished are some paintings. These include two of the most celebrated works of art in history: the Mona Lisa in the Louvre and The Last Supper in Milan. As a consequence, for centuries Da Vinci was regarded primarily as an artist, with his other interests relegated to hobby status. However, it has become increasingly apparent that his art was the key to his science.

In order to paint the human form better, he studied anatomy, dissecting many cadavers at a time when this was unusual, and drawing them in painstaking detail. He described the body like a machine, and even replaced muscles with strings to see how they worked with the levers of the bones. His investigation of optics and especially prisms foreshadowed Newton, and his work on shadows made him the supreme artist at depicting the human face in light and shade.

As an artist, he was fascinated by the eye and was sceptical of the Ancient Greek view that the eye illuminated those objects it saw. If that were true, he suggested, upon opening our eyes we would see closest things first and distant things like the sun only when the light had had time to travel out and back again. It is also evident that he was very close to developing the scientific method. Rather than simply believing what he was told, Da Vinci valued scientific observation, saying that one should perform an experiment and make up one's own mind.

Surprisingly, one of his most complete scientific achievements was in geology. Many scientists, as late as the nineteenth century, refused to believe that the world was not created as we see it, but that it had formed over many years. Most believed in the 'biblical' age of the earth, some 4 000 years. Yet 300 years earlier, Da Vinci had already formulated the idea of geological time, following his involvement in canal building and his insatiable curiosity that led him to investigate the exposed rocks. His observations led him to believe that valleys are carved by rivers, that the sea-level can fall to reveal mountains, and that this all happened over a huge period of time.

If this work had been published in an intelligible form, Da Vinci's place as a pioneering scientist would have been beyond dispute. Yet his true genius was not as a scientist or an artist, but as a combination of the two: an 'artist-engineer'. His painting was scientific, based on a deep understanding of the workings of the human body and the physics of light and shade. His science was expressed through art, and his drawings and diagrams show what he meant, and how he understood the world to work.