Galileo, who was
born in 1564 (about forty years after Leonardo's death), is
regarded by historians of science as the greatest thinker in the
realm of motion and matter up to Newton's time. It is generally
agreed that his practical demonstrations paved the way for Newton's
own blend of experimental verification and mathematical
integrity.
Galileo's work in
this area was revolutionary because he was the first to devise
repeatable experiments that showed that Aristotle's ideas were
quite wrong. He is probably most famous for his use of the
telescope, which destroyed the traditional ideas of how the solar
system is constructed but equally important for the progress of
science was his work in what became known as the science of
dynamics.
Aristotle held that
bodies were either intrinsically light or heavy and they fell at
different velocities because of their innate tendency to seek their
natural places. In 1590 the Flemish philosopher Simon Stevin had
shown that light and heavy objects falling through a vacuum reach
the ground simultaneously. Galileo repeated this experiment the
following year (although probably not from the Leaning Tower of
Pisa as tradition had it) using a cannonball and a musket-ball and
showed that the two fall at equal speed if the resistance of air is
ignored.
More importantly,
Galileo suspected from this experiment that a falling body moves
with a speed proportional to the time it has been falling. But,
because the balls fall too quickly for the eye to measure their
actual speed, he could not formulate a mathematical relationship
between the speed of descent and the time it took. In order to find
this relationship, he needed to conduct an experiment in which the
speed of descent could be measured.
He quickly
established that, ignoring friction, an object rolling own an
inclined plane acquires the same speed as it would if it was
falling vertically through the same distance. This enabled him to
construct a series of experiments in which he let balls roll along
inclined planes and measured the time of their journey and the
speeds. This confirmed that the speed of a falling object does
indeed increase with the time of the fall.
In a variation on
this experiment, he allowed a ball to roll down an inclined plane
and roll up another. In a further test, he allowed the ball to
travel on beyond the slope along a horizontal path, where it
continued steadily until slowed and eventually stopped by
friction
It was these
experiments that convinced Galileo that Aristotle's idea of the
Unmoved Mover was false. Objects do not move because they are
constantly being pushed or pulled: rather, they possess inertia -
an innate tendency to move unless stopped.
This was a
revolutionary notion, but his views on other questions concerning
matter and energy also entitle Galileo to be seen as the first of
the modernists.
Galileo rejected
Aristotle's idea of the four elements and subscribed to
Democritus's atomic theory at least three decades before it began
to make a reappearance in the schemes of Europe's leading thinkers,
though he was unable to prove it. He also flew in the face of
Aristotle's insistence that objects possess integrally all the
properties we sense when we observe them, declaring:
"I feel
myself impelled by necessity, as soon as I conceive a piece of
matter or corporal substance, of conceiving that in its nature it
is bounded and figured by such and such a figure, that in relation
to others it is large or small, that it is in this or that place,
in this or that time, that it is in motion or remains at rest, that
it touches or does not touch another body, that it is single, few
or many; in short by no imagination can a body be separated from
such conditions. But that it must be white or red, bitter or sweet,
sounding or mute, of a pleasant or unpleasant odour, I do not
perceive my mind forced to acknowledge it accompanied by such
conditions; so if the senses were not the escorts perhaps the
reason or the imagination by itself would never have arrived at
them. Hence I think that those tastes, odours, colours etc. on the
side of the object in which they exist, are nothing else but mere
names, but hold their residence solely in the sensitive body; so
that if the animal were moved, every such quality would be
abolished and annihilated.
So contrary to
Aristotle, Galileo states categorically that there are distinct
qualities of bodies. The first may be considered primary ties which
are inseparable from and fundamental to the nature of the object in
question - what twentieth-century scientists would ascribe to the
atomic structure and chemical nature of an object. The others are
secondary qualities, which are interpreted by the senses of the
observer.
These revolutionary
notions of Galileo's - ideas which have perhaps been swamped by his
more famous discoveries in astronomy and dynamics - greatly
influenced the French philosopher Rene Descartes, who for a time
informed Newton's thinking on the subject of matter and the nature
of the physical universe.
