1 The Birth of Science - MSRI

11.5 Two Modern Scientists: Kepler and Descartes 313
overarching natural philosophy explanations for how nature behaves. For
almost two thousand years, no scientist in this mold had been seen.
Another point to be stressed is that the rift between mathematics and
physics, whose absence is often read as a sign of the primitive state of
Hellenistic science, is not yet present in Galileo’s work. He follows exactly
the example of his distant masters, blending together mathematics and
experiments. 88 Physics as opposed to mathematics had not arisen yet.
11.5 Two Modern Scientists: Kepler and Descartes
Galileo’s lucid rationalism represents a methodological attitude exceptional
among early modern scientists. Kepler, who played a giant role
in the formation of modern science, had quite a different approach. His
eclectic spirit drew on an ample gamut of sources — Hellenistic science,
Aristotelian and neo-Platonic philosophy, neo-Pythagorean numerology,
astrology, alchemy — and amalgamated it all with the glue of theology.
His scientific method may be illustrated with excerpts from his writings.
About tides, for example, he writes:
Experience shows that everything that is made of moisture swells up
when the moon waxes and shrinks back when it wanes. 89
Kepler derives the distances of the planets from their correspondence
with Platonic solids and metals: he believes in the celestial musical harmonies
and the crystalline sphere of fixed stars. Here is how he describes
the structure of the universe:
The philosophy of Copernicus matches the main parts of the world
[universe] to different regions of the world’s shape. For just as the
sphere, image of God the Creator and archetype of the world (as
shown in Book I), has three regions, symbolizing the three persons
of the Holy Trinity — the center corresponding to the Father, the surface
to the Son and the in-between to the Holy Spirit — so three main
parts of the world were created, each in its part of the spherical
shape: the sun in the center, the sphere of fixed stars on the surface
and finally the planetary system in the region in between. 90
88
In this connection it is illuminating to read the pages in the second day of the Dialogues and
demonstrations showing how the shape of machines and animals depends on their dimensions. I
don’t know of a similarly limpid and example-rich account in ancient literature, though the general
idea is present in Vitruvius (De architectura, X, xvi, 5).
89
J. Kepler, De fundamentis astrologiae certioribus, thesis XV (Prague, 1601) = [Kepler: OO], vol. I,
p. 422.
90
J. Kepler, Epitome astronomiae copernicanae (Linz, 1618), book IV, part I, section I = [Kepler: OO],
vol. VI, p. 310.
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