I would like to make you more sensible by a comparison of this effect of the social and intellectual state on the Fine Arts. Suppose you are leaving the land of the south for that of the north; you perceive on entering a certain zone a particular mode of cultivation and a particular species of plant: first come the aloe and the orange; a little later, the vine and the olive; after these, the oak and the chestnut; a little further on, oats and the pine, and finally, mosses and lichens. Each zone has its own mode of cultivation and peculiar vegetation; both begin at the commencement, and both finish at the end of the zone; both are attached to it. The zone is the condition of their existence; by its presence or its absence is determined what shall appear and what shall disappear. Now, what is this zone but a certain temperature; in other words, a certain degree of heat and moisture; in short, a certain number of governing circumstances analogous in its germ to that which we called a moment ago the social and intellectual state? Just as there is a physical temperature, which by its variations determines the appearance of this or that species of plant, so is there a moral temperature, which by its variations determines the appearance of this or that species of art. And as we study the physical temperature in order to comprehend the advent of this or that species of plants, whether maize or oats, the orange or the pine, so is it necessary to study the moral temperature in order to comprehend the advent of various phases of art, whether pagan sculpture or realistic painting, mystic architecture or classic literature, voluptuous music or ideal poetry. The productions of the human mind, like those of animated nature, can only be explained by their _milieu._