force and potential energy, and reduce a universe to ether movement. Space and time were not fundamental ideas, but, as Kant had said, mere subjective notions. We measure time by a change of space relation; that is, a movement of a star, of the earth, of a clock hand. "In a world void of all kind of movement there would not be seen the slightest sequence in the internal state of substance. Hence the abolition of the relation of substances to one another, carries with it the annihilation of sequence and of time." Thus everything was made to depend upon movement. The equations of motion became the chief instruments of physical research, and the criterion by which the results of experiments were interpreted. Galileo lost his professorship because he dared to dispute the authority of Aristotle. Daguerre was, for a time, placed in an asylum because he said he could take a picture on a tin plate. Galvani was ridiculed by his friends, and dubbed "the frog's dancing master." Franklin's paper on lightning conductors was considered foolish, and refused publication by the Royal Society. Fifteen years ago it would have been almost as disastrous for a physicist to question the authority of La Grange or Maxwell. Not only were the results of experiments subjected to mathematical analysis, the direction of scientific investigation was largely so determined. The question was first put to mechanics. If a positive answer was indicated the question was put to nature and the research went on. If the equations indicated a negative result the question was dropped and the research abandoned.
Physics was an exact science. Other sciences were not exact sciences because their theories and hypotheses could not be mathematically expressed—the relation between cause and effect was not expressible in algebraical symbols. Physics was an exact science whose fundamental principles had been discovered and its laws expressed by equations. All that remained to be done was to make more accurate measurements of physical quantities for use as coefficients and exponents.
Let me quote from the 1894 catalogue, and later catalogues, of one of the largest universities in the United States.
While it is never safe to affirm that the future of physical science has no marvels in store. . . . , it seems probable that most of the grand underlying principles have been firmly established and that further advances are to be sought chiefly in the rigorous application of these principles to all the phenomena which come under our notice. . . . An eminent scientist has remarked that the future truths of physical science are to be looked for in the sixth place of decimals.
The foregoing is a verbatim quotation from the introductory statement preceding the list of courses in physics offered at one of our great universities, written, I think, in 1894. "Underlying principles firmly established." "Future truths in sixth decimal place," 1894. Then came the discovery of Rontgen rays, 1895; Becquerel rays, 1896; Zee-
