A general situation, provoking tendencies and special faculties; a representative man, embodying these predominant tendencies and faculties; sounds, forms, colors, or language giving this character sensuous form, or which comport with the tendencies and faculties comprising it, such are the four terms of the series; the first carries with it the second, the second the third, and the third the fourth, so that the slightest variation of either involves a corresponding variation in those that follow, and reveals a corresponding variation in those that precede it, permitting abstract reasoning in either direction in an ascending or descending scale of progression.[1] As far as I am capable of judging, this formula embraces everything. If, now, we insert between these diverse terms the accessory causes occurring to modify their effects; if, in order to explain the sentiments of an epoch, we add an examination of race to that of the social medium; if, in order to explain the works of art of any age, we consider, besides the prevailing tendencies of that age, the particular period of the art, and the particular sentiments of each artist, we shall then derive from the law not only the great revolutions and general forms of man's imagination, but, again, the differences between national schools, the incessant variations of various styles, and the original characteristics of the works of every great master. Thus followed out, such an explanation will be complete, since it furnishes at once the general traits of each school, and the distinctive traits which, in this school, characterize individuals. We are about to enter upon this study in relation to Italian art; it is a long and difficult task, and I have need of your attention in order to pursue it to the end. [Footnote 1: This law may be applied to the study of all literatures and to every art. The student may begin with the fourth term, proceeding from this to the first, strictly adhering to the order of the series.] X. Before proceeding further, gentlemen, there is a practical and personal conclusion due to our researches, and which is applicable to the present order of things.