tions, distances and altitudes, and the preparation of maps of appropriate scales, along with an empirical description of the facts observed. For those geographers, however, who, in these modern days, enter whole-souled into the explanatory method of describing land forms, there is needed, in addition to all the earlier requirements—for every modern geographer ought to be well exercised in the preparation of empirical descriptions, as well as in the arts of surveying and cartography—a careful and conscious training in theoretical investigation; because every explanatory description, in so far as it introduces the supposed facts of the past as the best means of describing the visible facts of the present, goes beyond observation and employs theories; and theories can be successfully established only by the critical use of scientific methods of investigation.
The different mental processes involved in an investigation of the kind with which we are here concerned may be arranged as follows: observation and record of accessible facts; induction of generalizations; search for fuller explanation; invention of hypotheses or supposed mental counterparts of invisible facts; deduction of consequences from each of the invented hypotheses; confrontation of the consequences with appropriate facts; preliminary judgment; revision and improvement of each process; final judgment of the degree of correctness of various invented hypotheses.
Observation and Record of Accessible Facts.—The first step in a problem is the acquisition of a certain number of facts. This may involve original observation, as in the outdoor exploration of a geographical field, or it may be based on second-hand observation, as in the study of some other observer's records in books and maps. In either case, the investigator must be alert to avoid deception by mistaken appearances and by misleading subjective sensations; at the same time the mind must be kept sensitive to every real impression, to which it must respond in the most docile manner, submissively recognizing the facts as they stand, not constraining them in the least one way or the other. The investigator must be untiringly active in traversing his outdoor field, and omnivorous in devouring all pertinent material in the library. Indeed during the process of acquisition, outdoors and indoors, the investigator's mind must be like a fresh and sensitive photographic plate, on which no previous impressions blur the new ones that are made on it.
The facts mentally acquired must in some way, graphic or verbal, be recorded; and at the outset the records should be made in colorless empirical form, as free as possible from theoretical prepossessions. It will be chiefly in proportion to the larger or smaller measure of previously acquired experience that the observer will, at this early stage of his study, employ roundabout phrases or technical terms in recording