29 4Chapter 16in mathematical formulae that were intended to be pre-
dictive. His vision, however, was mechanistic, not mys-
tical or organic.
Galileo’s exploration of the planets was inspired by
the invention of the telescope. The basic principles of
optics had been discovered by the Aristotelians, and
eyeglasses were introduced early in the sixteenth cen-
tury. By 1608 Dutch and Flemish lens grinders were
combining two lenses at fixed distances from one an-
other to create the first telescopes. Using a perfected
version of the telescope that he had built himself,
Galileo turned it upon the heavens (see illustration
16.2). The results created a sensation. His discovery of
the moons of Jupiter and the phases of Venus seemed
to support the Copernican theory, while his study ofsunspots raised the unsettling possibility that the Sun
rotated on its axis like the planets.
Perhaps because he was not interested in astrology,
Galileo ignored the problems of planetary motion that
obsessed Kepler. Instead he concentrated on the me-
chanics of motion. Kepler had established the position
of the planets with his Rudolphine Tablesof 1627 but had
been unable to explain either the causes of their motion
or what kept them in their orbits. The issue had per-
plexed the ancients because they believed that rest was
the normal state of any object. The Aristotelians had
argued that an object remains at rest unless a force is
applied against it and that the velocity of that object is
proportionate to the force exerted in moving it. As a re-
sult, finding an explanation for why a projectile contin-
ued to move after the impetus behind it had ceased was
difficult. Galileo turned the problem on its head by
proving that a body in motion will move forever unless
it is slowed or deflected by an external force and that
the application of uniform force results in acceleration
instead of motion at a constant rate. Movement is
therefore as natural a state as rest. Once it had been set
in motion by its Creator, the universe could in theory
go on forever without further intervention.
It was a profoundly disturbing vision. To Galileo,
God was the Great Craftsman who created the world as
a self-sustaining and predictable machine. To those
who saw the universe as an organic entity upon which
God still imposed His will, such a view was not only
frightening but also blasphemous. It brought Galileo
before the Papal Inquisition. He was tried because he
defended the Copernican system and because his ideas
undermined a worldview that had prevailed for nearly
two thousand years. Yet the importance of this cele-
brated trial should not be exaggerated. Galileo’s con-
demnation forced him to retire to his country villa; it
did not prevent him or any other Italian from proceed-
ing with research along the lines he had suggested.
Galileo was arrogant and bad-tempered with patrons
and opponents alike. He was also a brilliant writer and
publicist (see document 16.1). Had his ability to attract
enemies not equaled his genius, the episode might
never have occurred.
The mechanistic view of the universe was destined
to triumph over its predecessor, and the church would
not again mount a frontal attack against it. René
Descartes (1596–1650), the most influential philoso-
pher of his day, developed a mechanistic vision that at-
tempted to integrate philosophy, mathematics, and the
sciences into a coherent, unified theory. He failed, but
his efforts inspired others such as Pierre Gassendi
(1592–1655), who attempted to revive the atomic the-Illustration 16.2
Galileo’s Telescopes (c. 1610)With instruments like these
Galileo discovered the moons of Jupiter and launched a new era
in observational astronomy. He also gained support for his work
by donating them to wealthy patrons.