The historian who wishes to relate the history of painting in the nineteenth century is confronted with quite other demands than await him who undertakes the art of an earlier period. The greatest difficulty with which the latter has to cope is the deficiency of sources. He manifestly gropes in the dark with regard to the works of the masters as well as to the circumstances of their lives. After he has searched archives and libraries in order to collect his biographical material, the real critical problem awaits him. Even amongst the admittedly authentic works, those which are undated confront those whose chronology is certain. To these must be added those nameless ones, as to whose history there is a doubt; to these again, those whose origin is to be ascertained. It needs a quick eye to separate the schools and groups, and finally to recognise the notes which are peculiar to the master.
With none of these difficulties is the historian of modern art confronted. The painters of the nineteenth century have very seldom forgotten to attach a name and date to their works, and the circumstances of their lives are related with an accuracy that was, earlier, rarely the lot of the foremost men in history. It is all the more difficult, face to face with such a chaos of pictures, to discover the spiritual bond which connects them all, to construct a building out of the immense supply of accumulated bricks, the piled-up mass of rough material. The evolution of modern painting is more complicated and varied than that of the art of an earlier period, just as modern life itself is more complicated and varied than that of any previous age.
How quietly, slowly, and surely was the evolution of that older period carried out. One simple proportion was maintained between art and the universal life of culture. Customs, views of life and art, were so intimately bound up together, that the knowledge of the age in general naturally comprises that of art. Standing before some old altar-piece of the school of Cologne, it is as though one were watching in some broad high dome; everything is quiet all round, and the august figures in the picture lead their calm, grave existence in illustrious grandeur. The message of Christianity, "My kingdom is not of this world," meets in art, too, with a clear expression. Humility and devotion are joined together, making for a refinement in the feeling of life that is unsurpassed in its hieratic tenderness and gracious innocence. In the fifteenth century, the age of discoveries, a new spirit entered the world. Commerce and navigation discovered new worlds, painting discovered life. The . . .