October 8. 1830.
GALILEO, NEWTON, KEPLER, BACON.
Galileo was a great genius, and so was Newton; but it would take two or three Galileos and Newtons to make one Kepler.[1] It is in the order of Providence, that the inventive, generative, constitutive mind—the Kepler— should come first; and then that the patient and collective mind—the Newton—should follow, and elaborate the pregnant queries and illumining guesses of the former. The laws of the planetary system are, in fact, due to Kepler. There is not a more glorious achievement of scientific genius upon record, than Kepler's guesses, prophecies, and ultimate apprehension of the law[2] of the mean distances of the planets as connected with the periods of their revolutions round the sun. Gravitation, too, he had fully conceived; but, because it seemed inconsistent with some received observations on light, he gave it up, in allegiance, as he says, to Nature. Yet the idea vexed and haunted his mind; "Vexat me et lacessit," are his words, I believe.
We praise Newton's clearness and steadiness. He was clear and steady, no doubt, whilst working out, by the help of an admirable geometry, the idea brought forth by another. Newton had his ether, and could not rest in—he could not conceive—the idea of a law. He thought it a physical thing after all. As for his chronology, I believe, those who are most competent to judge, rely on it less and less every day. His lucubrations on Daniel and the Revelations seem to me little less than mere raving.
[Footnote 1:
Galileo Galilei was born at Pisa, on the 15th of February, 1564. John
Kepler was born at Weil, in the duchy of Wirtemberg, on the 2lst of
December, 1571.—ED.]
[Footnote 2: Namely, that the squares of their times vary as the cubes of their distances,—ED.]
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Personal experiment is necessary, in order to correct our own observation of the experiments which Nature herself makes for us—I mean, the phenomena of the universe. But then observation is, in turn, wanted to direct and substantiate the course of experiment. Experiments alone cannot advance knowledge, without observation; they amuse for a time, and then pass off the scene and leave no trace behind them.
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Bacon, when like himself—for no man was ever more inconsistent—says, "Prudens qiuestio—dimidium scientiæ est."