THE STUDY OF HISTORY 13

in another, and sheep grazing in a third. These differences are in part due to geography. And we still are unable to escape the effects of changes in the barometer upon our spirits. Indeed, recent experimental tests tend to confirm the general notion that physical and mental efficiency are greatest in a climate where the temperature is moderate and variable, and that a tropical climate weakens moral char- acter as well as decreases the capacity for intellectual and manual labor. • The question "When?" is no less important to the stu- dent of history than " Where?" To trace the progress of civilization and to understand historical relation- i mportance ships, it is necessary to know when things hap- of dates in , , ,-, , history pened or existed. Every important event has its causes and results, and to learn them we must know what preceded and followed the event. Human society in any place at any time consists of many particular things and persons, events and customs. These go together and what unites them is their simultaneous occurrence. They are a bundle of sticks which must be tied together with a date. Moreover, the effect of an event upon society depends greatly upon when it happened, for circumstances might be favorable at one time and not at another. It is true that many social conditions which have existed for a long period began and disappeared so gradually that it is impossible to date them precisely and one must be content with such approximate expressions as "the thirteenth century," "the early Roman Empire," and "the later Middle Ages." Other events which undoubtedly did happen within some particular year we are also unable to date because of lack of reliable source material. But the object of the historical student should be not so much to fix exact dates in his memory as to be able to list events in their proper sequence, to associate closely together all simultaneous happenings, and to cultivate a feeling for the lapse of time — to be able to realize, for instance, what five hundred years ago means. Of course among the lowest savages chronology is a mat- ter of slight utility, since their life develops little and there