Brunelleschi was not only the initiator of Renaissance architecture. To him, it seems, is due another momentous discovery in the field of art, which also dominated the art of subsequent centuries - that of perspective. We have seen that even the Greeks, who understood foreshadowing, and the Hellenistic painters, who were skilled in creating the illusion of depth, did not know the mathematical laws by which objects appear to diminish in size as they recede from us. We remember that no artist could have drawn the famous avenue of trees leading back into the picture until it vanishes into the horizon. It was Brunelleschi who gave artists mathematical means of solving this problem; and the excitement which this caused among his painter-friends must have been immense. -