Lionardo's turn for physical science led him to study the technicalities of art with fervent industry. Whatever his predecessors had acquired in the knowledge of materials, the chemistry of colours, the mathematics of composition, the laws of perspective, and the illusions of _chiaroscuro,_ he developed to the utmost. To find a darker darkness and a brighter brightness than had yet been shown upon the painter's canvas; to solve problems of foreshortening; to deceive the eye by finely graduated tones and subtle touches; to submit the freest play of form to simple figures of geometry in grouping, were among the objects he most earnestly pursued. At the same time his deep feeling for all things that have life, gave him new power in the delineation of external nature. The branching of flower-stems, the outlines of fig-leaves, the attitudes of beasts and birds in motion, the arching of the fan-palm, were rendered by him with the same consummate skill as the dimple on a cheek or the fine curves of a young man's lips.[242] Wherever he perceived a difficulty, he approached and conquered it. Love, which is the soul of art--Love, the bondslave of Beauty and the son of Poverty by Craft--led him to these triumphs. He used to buy caged birds in the marketplace that he might let them loose. He was attached to horses, and kept a sumptuous stable; and these he would draw in eccentric attitudes, studying their anatomy in detail for his statue of Francesco Sforza.[243] In the "Battle of the Standard," known to us only by a sketch of Rubens,[244] he gave passions to the horse--not human passion, nor yet merely equine--but such as horses might feel when placed upon a par with men. In like manner the warriors are fiery with bestial impulses--leonine fury, wolfish ferocity, fox-like cunning. Their very armour takes the shape of monstrous reptiles. To such an extent did the interchange of human and animal properties haunt Lionardo's fancy.