Years later, Galileo would describe his time at Padua
as the happiest years of his life. His first lecture, of which
no copy survives, achieved him great success, and he quickly became
friendly with a number of Venice's leading citizens. After surviving
a bout of financial trouble in early 1593, when the demands of
his family and particularly his sister's dowry almost overwhelmed
him, Galileo prospered, and eventually moved from a small cottage
into a larger three-story house. The house's grounds included
a walled garden where he often entertained students and other guests.
In 1599, at the end of his first seven- year term, the university
offered to renew his appointment, and Galileo gladly accepted.
By this point in time he was keeping a mistress, a Venetian woman
named Marina Gambi, who would bear him three children–two daughters,
in 1600 and 1601, and a son in 1606. Galileo recognized these
children as his heirs, despite their illegitimate status, but he
seems never to have considered marrying Marina. Scholars often
remained single during this time, and the aristocratic rank of
his family, especially on his mother's side, forbade him from marrying
anyone as common as Marina.
Meanwhile, although Galileo's lectures never won him a
great following, his scientific research was thriving. It was
during this period that he accomplished most of his work in the
field of physics, although he would not synthesize it until late
in life, when he published his Dialogues Concerning Two
New Sciences. He established the basic principles of the
lever and pulley, experimented with inclined planes, and eventually
formulated the law of inertia, which states that a body in motion
will continue moving indefinitely in one direction and at a constant
speed unless interfered with by another force. This law would
later become Sir Isaac Newton's famous first law of motion. At
the same time, perhaps inspired by his father's music, he posited
that musical notes were in fact wave lengths of air, and researched
the relationship between vibrations in a stringed instrument and
the pitch of the note produced.
But even as he did this work, a new interest was intruding
on his studies. This was astronomy, the study of the heavens,
and a field in much ferment during the 16th century. Throughout
the Middle Ages, astronomy had been dominated by the theory of
geocentricity, which held that the earth lay at the center of the
universe, and the sun–and the other planets–revolved around it.
This theory, which had been rigorously upheld by Aristotle
and the ancient astronomer Ptolemy, fit in neatly with the Catholic Church's
view of the universe, as well as with every day common sense: to
the casual observer, it seemed common sense that the sun "rose"
in the morning and "set" at night, in its circling pattern around
the earth. As a scientific system, however, geocentricity required
a complex scheme of interlocking orbits, one that became more complex
and convoluted with each passing century, as Ptolemy's successors
attempted to "save the phenomena," as they put it–that is, to make
their system accommodate the evidence of their observations.
The Ptolemaic system was a brilliant feat of geometric
precision, despite being mistaken about the actual nature of the
"phenomena" it attempted to describe. But in the 16th century,
geocentricity fell under attack. The first to question it was
Nicholas Copernicus, a Polish astronomer, whose work On
the Revolution of Heavenly Orbs (published after his death,
in 1543) proposed a heliocentric system, in which the planets,
including the earth, orbited the sun.
This system, Copernicus argued, arranged the known universe
in a more mathematically satisfying way; but he was careful to
make no claims to scientific truth. Indeed, such a claim would
have had no real basis at the time: the available facts, most scientists
agreed, did not support a wholesale abandonment of Ptolemy's system.
Later, the great Danish astronomer Tycho Brahe (1546- 1601), who made
countless stellar observations from his island observatory, rejected
Copernicus's scheme entirely. But the younger generation of astronomers
began to embrace it, among them Brahe's pupil Johannes Kepler (1571-1630),
who discovered the laws of planetary motion and whose Mysterium
Cosmographicum (1596) fiercely advocated the Copernican
system, albeit with some modifications.
