This booklet contains the substance of a course of lectures given at the Women's University Extension in Antwerp, during the scholastic year 1897-1898. This explains sufficiently the plan and style of the work. There was question of presenting to an intelligent audience the great lines of a tableau, which must be surveyed at one glance, if one wishes to grasp its vast and striking unity. Friendly critics have asked me to give ref crenees for the statements made. I have not deemed it wise to burden with annotations lectures which aim to present ideas rather than to state facts. As will be seen, I take it for granted that the latter are known to the reader, and I trust that he will take my word for occasional statements of facts with which he may not be familiar.