On the other hand, the great resemblance which the arts of a single time and country bear to each other, is accounted for by the fact that their creators look upon the external facts of life through a glass, if we may put it so, tinted with the colours of the national genius. They bring to their study of an eternal model the same transient prejudices, the same preoccupations, the same desires. And yet among those highly gifted races where art holds or has held a lofty place, groups of artists are formed, either successively or simultaneously, which we call schools. Each of these groups professes to make a fresh reference to nature, to interpret her works more faithfully than its predecessors, and to draw from them typical forms which shall be more expressive of the real desires and sentiments of the public for which it caters. Between the works of these different schools, there are, however, many similarities, which are to be explained by the identity of race and belief. There are also diversities which are caused either by different conditions or by the influence of some master spirit. Wherever these schools spring up, art lives, moves, and progresses. But sooner or later comes a time when this ardour comes to an end, and exhaustion takes its place. The civilization to which it belongs becomes old and languid, and its creative power ceases like the imperceptible sinking of a flood. Now, it often happens that just before this period of lassitude, in the last days of reproductive strength and healthy maturity, a rich and brilliant school springs up, which interprets the characteristic sentiments of the civilization to which it belongs, with the greatest vigour and by admirably selected means. If such an interpretation be found satisfactory at all points, why should a better be sought for at the risk of choosing a worse? This question is but a confession of impotence on the part of those who ask it. From that moment convention will be supreme, and convention in the sense of an artificial set of rules which will release the artist from his obligation of continual reference to nature. [Illustration: FIG. 52.--Sculptor at work upon an arm, Thebes. (Champollion, pl. 180.)]