military struggles of primitive savage tribes, “_new institutions, new activities, new ideas, all_,” he says, “_unobtrusively make their appearance, without the aid of any king or legislator; and if you wish to understand the phenomena of social evolution, you will not do it, should you read yourself blind over the biographies of all the great rulers on record, down to Frederick the Greedy, and Napoleon the Treacherous_.” And he points his moral by observing, with a certain philosophic tartness, that there is no surer index of a man’s “_mental sanity_” than the degree of contempt which, as a scientific thinker, he feels for the class of facts which the biography of individuals offers him. Such, then, being Mr. Spencer’s theory of the way in which social phenomena must be regarded, if we mean to make them the subject of anything like scientific study, let us turn to his _magnum opus_, _The Principles of Sociology_, and see how, and with what results, he puts his theory of study into practice. This immense work, full of encyclopædic detail as it is, contains certain general and comparatively simple conclusions, which can with sufficient clearness be expressed in a short summary, and which are typical of the character and the contents of Mr. Spencer’s sociology as a whole. These general conclusions constitute in {29} outline the entire history of human progress from the dawn of man’s existence to the industrial civilisation of to-day. The determining factors in all social phenomena are, says Mr. Spencer, primarily of two kinds—the “_external_” and the “_internal_.” The former consist of some of the various physical circumstances in which each community or collection of men is placed; the latter consist of the characters and constitutions of the men themselves. In the history of each community the chief of the external factors are these: the climate of the region which the community occupies; the cultivability of this region; its geological and geographical character; the way in which the fauna and flora natural to it are distributed; and the character of the other communities by which the community in question is surrounded. One of the first generalisations, says Mr. Spencer, to which social science leads is this—that progress can begin only in climates and regions where the production of the necessaries of life is sufficiently easy to leave men leisure and energy available for other work; and all progress did as a fact begin in those parts of the earth where the maintenance of life was easy.