Giotto was succeeded by a host of lesser men, regarded as his followers, men who sought to apply the principles and methods of painting worked out by the master, but who lacked his inspiration and his power. Thus it was for nearly a hundred years. The turn of the fourteenth century into the fifteenth saw the emergence of new forces in the science and the mechanics of painting. The laws of perspective and foreshortening were made the object of special research and practice by men like Uccello (1397-1475), Piero dei Franceschi (1416-1492), and Mantegna (1431-1506). "Oh, what a beautiful thing this perspective is!" Uccello exclaimed, as he stood at his desk between midnight and dawn while his wife begged him to take some rest. In the first thirty years of the fifteenth century, Masaccio contributed to the knowledge of anatomy by his painting of the nude form; and the study of the nude was continued by Pollaiuolo and Luca Signorelli, in the second half of the century. Masaccio, also, was the first to place his figures in _air,_ enveloping them in atmosphere. Verrocchio, a generation later than Masaccio, was one of the first of the Florentines to understand landscape and the part played in it by air and light. The realistic spirit, which suffices itself with subjects drawn from every-day actual experience, finds expression in the first half of the fifteenth century in the work of Andrea del Castagno. And so down through that century of spring and summer. Each painter in his own way carries some detail of his craft to a further point of development and prepares the path for the supreme triumphs of Michelangelo, Leonardo, and Raphael.