358 BULLETIN OF THE 



to "the seeds of great discoreries constantly floating around us," 

 • — the careful observation, the clear perception of the actual facts 

 uncolored as much as possible by a priori conceptions or expec- 

 tations, — the faculty of persevering watchfulness, and the judg- 

 ment to eliminate (with all due caution) the conditions which are 

 accidental, — the importance of a provisional hypothesis, — the 

 conscientious and impartial testing of such by every expedient that 

 ingenuity may suggest, — the lessons taught by failure, — the firm 

 holding of tlie additional facts thus gleaned, though adverse and 

 disappointing, — the diligent pondering, and the logical applica- 

 tion of deductive consequences, to be again examined until as the 

 reward of patient solicitation, the answer of nature is at last re- 

 vealed. 



"The investigator now feels amply rewarded for all his toil, 

 and is conscious of the pleasure of the self-appreciation which 

 flows from having been initiated into the secrets of nature, and 

 allowed the place not merely of an humble worshipper in the ves- 

 tibule of the temple of science, but an officiating priest at the 

 altar. In this sketch which I have given of a successful investi- 

 gation, it will be observed that several faculties of the mind are 

 called into operation. First, the imagination, which calls forth 

 the forms of things unseen and gives them a local habitation, 

 must be active in presenting to the mind's eye a definite concep- 

 tion of the modes of operation of the forces in nature sufficient to 

 produce the phenomena in question. Second, the logical power 

 must be trained in order to deduce from the assumed premises 

 the conclusions necessary to test the truth of the assumption in 

 the form of aa experiment, and again the ingenuity must be taxed 

 to invent the experiment or to bring about the arrangement of 

 apparatus adapted to test the conclusions. These faculties of 

 mind may all be much improved and strengthened by practice. 

 The most important requisite, however, to scientific investigations 

 of this character, is a mind well stored with clear conceptions of 

 scientific generalizations, and possessed of sagacity in tracing 

 analogies and devising hypotheses. Without the use of hypotlieses 

 or antecedent probabilities, as a general rule no extended series 

 of investigations can be made as to the approximate cause of casual 

 phenomena. They require to be used however with great care, 

 lest they become false guides whicli lead to error rather tlian to 

 truth."* Who that listened could f-.iil to see that the speaker 

 was unconsciously giving us precious glimpses into his own expe- 

 rience? 



Less than two weeks after this, he sufiFered at New York a tem- 

 porary numbness in his hands, which he feared might threaten a 

 paralysis ; but a subsequent swelling of his feet and hands revealed 



* Bulletin Phil. Soc. Washington, Nov. 24, 1877, vol. ii. p. 166. 



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