serve as starting-points for series of vast transformations. A drove of horses brought by the Spanish has stocked the whole of South America. In a flood a branch of a tree may dam a current and transform the aspect of a valley.
In human evolution we meet with great transformations which have no intelligible cause beyond an individual accident. In the sixteenth century England changed its religion three times on the death of a sovereign (Henry VIII., Edward VI., Mary). Importance not to be measured by the initial fact, but by the facts which resulted from it. We must not, therefore, deny a priori the action of individuals and discard individual facts. We must examine whether a given individual was in a position to make his influence strongly felt. There are two cases in which we may assume that he was: (1) when his action served as an example to a mass of men and created a tradition, a case frequent in art, science, religion, and technical matters; (2) when he had power to issue commands and direct the actions of a mass of men, as is the case with the heads of a state, an army, or a church. The episodes in a man's life may thus become important facts.
Accordingly, in the scheme of historical classification a place should be assigned for persons and events.
VI. In every study of successive facts it is necessary to provide a number of halting-places, to distinguish beginnings and ends, in order that chronological divisions may be made in the enormous mass of facts. These divisions are periods; the use of them is as old as history. We need them, not only in general history, but in the