358 MEMORIAL OF JOSEPH HENRY. 



mental and bodily powers, we little thought was in reality his 

 valedictory. In it he concisely yet lucidly portrayed for the stimu- 

 lation of more youthful physicists, the processes and the qualities 

 necessary for success in original research; the awakened attention 

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

 the careful observation, the clear perception of the actual facts 

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

 tions, the faculty of persevering watchfulness, and the judgment 

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

 dental, the importance of a provisional hypothesis, the con- 

 scientious and impartial testing of such by every expedient that 

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

 holding of the additional facts thus gleaned, though adverse and 

 disappointing, the diligent pondering, and the logical application 

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

 of patient solicitation, the answer of nature is at least revealed. 



"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 vestibule of 

 the temple of science, but an officiating priest at the altar. In this 

 sketch which I have given of a successful investigation, 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 conception 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 an experiment; and again the inge- 

 nuity 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 



