SOURCE: “The Notebooks,” in Leonardo da Vinci: An Account of His Development as an Artist, Penguin, 1973, pp. 60-71.

In the following essay, which was first published in 1939, Clark surveys the content of the notebooks Leonardo kept, observing that Leonardo's writings are characteristically thorough.

To the early years of Leonardo's residence in Milan belong the first of those notebooks and manuscripts which, for the remainder of his life, give us a full record of his activities, both practical and scientific. It is a curious fact that these records only begin when Leonardo was thirty, an age when the average busy man ceases to take notes; yet the few scraps surviving from the earlier period of his life do not suggest that he was then in the habit of recording his interests, or indeed, that his interests were very wide. They consist of some drawings of machinery and engines of...