He learned here the art of going deep, of tracking the sources of expression to their subtlest retreats, the power of an intimate presence in the things he handled. He did not at once or entirely desert his art; only he was no longer the cheerful objective painter, through whose soul, as through clear glass, the bright figures of Florentine life, only made a little mellower and more pensive by the transit, passed on to the white wall. He wasted many days in curious tricks of design, seeming to lose himself in the spinning of intricate devices of lines and colours. He was smitten with a love of the impossible--the perforation of mountains, changing the course of rivers, raising great buildings, such as the church of San Giovanni, in the air; all those feats for the performance of which natural magic professes to have the key. Later writers, indeed, see in these efforts an anticipation of modern mechanics; in him they were rather dreams, thrown off by the over-wrought and labouring brain. Two ideas were especially fixed in him, as reflexes of things that had touched his brain in childhood beyond the measure of other impressions--the smiling of women and the motion of great waters....
The science of that age was all divination, clairvoyance, unsubjected to our exact modern formulas, seeking in an instant of vision to concentrate a thousand experiences. Later writers, thinking only of the well-ordered treatise on painting which a Frenchman, Raffaelle du Fresne, a hundred years afterwards, compiled from Leonardo's bewildered manuscripts, written strangely as his manner was, from right to left, have imagined a rigid order in his inquiries. But this rigid order was little in accordance with the restlessness of his character; and if we think of him as the mere reasoner who subjects design to anatomy, and composition to mathematical rules, we shall hardly have of him that impression which those about him received from him. Poring over his crucibles, making experiments with colour, trying by a strange variation of the alchemist's dream to discover the secret, not of an elixir to make man's natural life immortal, but rather giving immortality to the subtlest and most delicate effects of painting, he seemed to them rather the sorcerer or the magician, possessed of curious secrets and a hidden knowledge, living in a world of which he alone possessed the key. What his philosophy seems to have been most like is that of Paracelsus or Cardan; and much of the spirit of the older alchemy still hangs about it, with its confidence in short cuts and odd byways to knowledge. To him philosophy was to be something giving strange swiftness and double sight, divining the sources of springs beneath the earth or of expression beneath the human countenance, clairvoyant of occult gifts in common or uncommon things, in the reed at the brook-side or the star which draws near to us but once in a century. How in this way the clear purpose was overclouded, the fine chaser's head perplexed, we but dimly see; the mystery which at no point quite lifts from Leonardo's life is deepest here. But it is certain that at one period of his life he had almost ceased to be an artist.