A discoverer is a tester of scientific ideas; he must not only be able to imagine likely hypotheses, and to select suitable ones for investigation, but, as hypotheses may be true or untrue, he must also be competent to invent appropriate experiments for testing them, and to devise the requisite apparatus and arrangements.
The Art of Scientific Discovery, Part III, Chapter XXXII (p. 306), Longmans, Green & Co. 1878