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.]
* * * * *
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.
* * * * *
Bacon, when like himself--for no man was ever more inconsistent--says,
_"Prudens qiuestio--dimidium scientiæ est."_
_October_ 20. 1830.