Examined thus closely, and by the trained eyes of professional artists provided with all the necessary instruments, the relics of antiquity yielded up secrets which would never have been suspected by the casual observer. Thus Mr. Penrose discovered and explained that those walls of the Propylæum and of the Parthenon, which seemed straight to the eye, are in fact planned on a gentle curve;[15] he showed how this subtle variation was calculated to add to the beauty of the buildings, and to augment their effect. Hittorf arrived at still more important results through the minute examination of the Sicilian ruins. He was the first to describe the important part which painting played in the decoration of Greek architecture; he affirmed that in many parts of their buildings the stone or marble was painted over, and that the various members of the architecture were distinguished by differences of tint, which gave accent to the mouldings, and force to the figures in relief. These ideas were too strongly opposed to modern habits of thought to be received without strong protestations. Their partisans, too, did something to retard their acceptance by their absolute fashion of stating their convictions, and by certain unhappy applications of their system; but the polychromatic principles of the Greeks are now confirmed by too many facts to be denied.[16] [15] F. C. PENROSE, _An Investigation of the Principles of Athenian Architecture_. Folio, with plates. London, 1851. [16] J. J. HITTORF, _Restitution du Temple d'Empédocle à Sèlinonte; ou, l'Architecture polychrome chez les Grecs_, 4to. and plates in folio. Paris, 1851.