Invention of Hypotheses.—The search for explanation of observed facts may be made in some cases by the memory, which may recall an explanation previously learned. In physics and chemistry, the search for explanation is largely aided by experiment; but in the study of land forms experiment serves chiefly to illustrate explanations already reached, rather than to lead to new ones. We are here chiefly concerned with the kind of search which calls the investigator's own faculty of invention into play—the kind of search which tries to make a new combination of some pertinent facts or principles of previous acquisition with some of the facts of new observation, in the hope of thereby bringing about a clear understanding of all the facts under discussion.
The faculty of invention is peculiar in working to a large extent subconsciously. Facts to be explained can be intentionally observed; previously gained knowledge may for the most part be consciously reviewed; but the desired explanatory combination of old knowledge and new facts may not be immediately found while the conscious search for it is going on. Invention is, however, much favored by active observation, and spurred on by an eager spirit of inquiry; it is greatly aided by mental ingenuity, but it is seldom immediately accomplished by conscious intention. However, the faculty of invention can be cultivated if many facts, old and new, are frequently brought to conscious attention, and the wish for explanation and the search for it are often renewed. Then the subconscious mind will continue the search, and after an interval, during which the matter has been apparently out of mind, an explanation may most unexpectedly awaken attention by springing into consciousness.
The sudden birth of an apparently successful explanation is truly a most delightful experience; indeed so delightful and encouraging that many an investigator has mistaken it for the climax or crown of his work, and accepted it as the whole truth without further question. But, as has already been pointed out, the too-ready acceptance of an untested invention, as if it were true, is dangerous. The investigator must recognize that it is no great recommendation of an invention, that it explains the partial group of facts that it was made to explain. Of course it must do that; it would deserve no consideration at all if it did not. But in order to deserve acceptance as the true counterpart of past facts, it must do much more. It must explain various facts that it was not made to explain; facts that it did not expect to explain; facts that were not thought of, or were not even known at the time of invention, as will appear more fully below.
The investigator of course hopes that his invention, based on some of the observed facts, will prove to be the true counterpart of some past facts, or of some invisible principle or process, by means of which