Leonardo, whose birth antedates that of Michelangelo and Raphael by twenty three and thirty-one years respectively, was thus in the forefront of the Florentine Renaissance, his life coinciding almost exactly with the best period of Tuscan painting.

Leonardo was the first to investigate scientifically and to apply to art the laws of light and shade, though the preliminary investigations of Piero della Francesca deserve to be recorded.

He observed with strict accuracy the subtleties of chiaroscuro—light and shade apart from colour; but, as one critic has pointed out, his gift of chiaroscuro cost the colour-life of many a noble picture. Leonardo was "a tonist, not a colourist," before whom the whole book of nature lay open.

It was not instability of character but versatility of mind which caused him to undertake many things that having commenced he afterwards abandoned, and the probability is that as soon as he saw exactly how he could solve any difficulty which presented itself, he put on one side the merely perfunctory execution of such a task.

In the Forster collection in the Victoria and Albert museum three of Leonardo's note-books with sketches are preserved, and it is stated that it was his practice to carry about with him, attached to his girdle, a little book for making sketches. They prove that he was left-handed and wrote from right to left.