1 14 THE POPULAR SCIENCE MONTHLY 



on in the dark with the eyes shut. During the exercise of this faculty 

 the investigator must in the most critical manner and with the aid of 

 all necessary pertinent knowledge, think out or deduce everything that 

 would happen, if an invented hypothesis were really true; and this he 

 must do for each hypothesis in turn. The consequences appropriate 

 to each hypothesis must be kept in groups by themselves; and these 

 groups of hypothetical consequences must be carefully distinguished 

 from the facts of observation. 



In a geographical problem, the investigator must mentally search 

 out, in view of each hypothesis that he has invented, the whole sequence 

 of changes that would take place, the whole sequence of land forms 

 that would be developed, if the class of forms with which he is dealing 

 were followed all through its history, past, present and future. No 

 invention should be hastily discarded, because it appears at first sight 

 to be improbable ; for such appearance may be more determined by the 

 scientific fashion of the time, or by the mental habit of the investigator, 

 than by anything inherent in the invention itself. Particular atten- 

 tion should be given to the deduction of unlike consequences of rival 

 hypotheses ; for, as will soon appear, it is particularly by means of these 

 instantice crucis that successful and unsuccessful hypotheses are dis- 

 criminated. Those who find deduction irksome should be advised to 

 practise it until it becomes easy and agreeable ; just as careless observers 

 should be urged to continue observation until they can perform this 

 fundamental process with accuracy and enjoyment. In no case should 

 an investigator, particularly an unpractised investigator, put his trust 

 in that rapid mental process called intuition, and hope by its uncertain 

 aid to leap from invention to conviction. Let intuition be welcomed, 

 just as invention is ; but after it has leaped to its goal, its half-conscious 

 path should be carefully retraced and the safety of its leap tested. 



Confrontation of Consequences with Facts. — We now reach a stage 

 in which the faculty of impartial comparison is brought into play. 

 Facts have been gathered abundantly by the active observer, who is 

 still at work gathering yet more of them ; hypotheses have been brought 

 forward in good number by the ingenious inventor, who is, however, 

 still at work in the hope to find new ones; the consequences of each 

 hypothesis have been carefully worked out, group by group, by the 

 patient and logical deducer, who stands ready to elaborate the conse- 

 quences of new hypotheses as soon as they are found; and the conse- 

 quences are now to be confronted, group after group, with the facts by 

 the impartial comparer, in order to see how close an agreement they 

 reach. This is as if the observer should marshal his battallion of facts 

 in good order on one side of a parade ground, and the deducer should 

 lead forth the battalions of consequences one after another and halt 

 them opposite the marshalled facts, so that the comparer could to best 



