Padua

But Galileo knew how to get what he wanted. He had obtained the Pisa post with
the help of the Marquis Guidobaldo del Monte, an influential nobleman and
competent mathematician. Galileo now aimed for the recently vacated chair of
mathematics at the University of Padua, and his chief backer in Padua was Gianvincenzio
Pinelli, a powerful influence in the cultural and intellectual life of
Padua. Galileo followed Pinelli’s advice, charmed the examiners, and won the
approval of the Venetian senate (Padua was located in the Republic of Venice,
about twenty miles west of the city of Venice). His inaugural lecture was a
sensation.
Padua offered a far more congenial atmosphere for Galileo’s talents and lifestyle
than the intellectual backwater he had found in Pisa. In the nearby city of
Venice, he found recreation and more—aristocratic friends. Galileo’s favorite debating
partner among these was Gianfrancesco Sagredo, a wealthy nobleman with
an eccentric manner Galileo could appreciate. With his wit and flair for polemics,
Galileo was soon at home in the city’s salons. He took a mistress, Marina Gamba,
described by one of Galileo’s biographers, James Reston, Jr., as “hot-tempered,
strapping, lusty and probably illiterate.” Galileo and Marina had three children:
two daughters, Virginia and Livia, and a son, Vincenzo. In later life, when tragedy
loomed, Galileo found great comfort in the company of his elder daughter,
Virginia.
During his eighteen years in Padua (1592–1610), Galileo made some of his
most important discoveries in mechanics and astronomy. From careful observations,
he formulated the “times-squared” law, which states that the vertical distance
covered by an object in free fall or along an inclined plane is proportional
to the square of the time of the fall. (In modern notation, the equation for free
fall is expressed , with s and t the vertical distance and time of the fall,
gt2
s
2
and g the acceleration of gravity.) He defined the laws of projected motion with
a controlled version of the Tower experiment in which a ball rolled down an
inclined plane on a table, then left the table horizontally or obliquely and
dropped to the floor. Galileo found that he could make calculations that agreed
approximately with his experiments by resolving projected motion into two components,
one horizontal and the other vertical. The horizontal component was
determined by the speed of the ball when it left the table, and was “conserved”—
that is, it did not subsequently change. The vertical component, due to the ball’s
weight, followed the times-squared rule.
For many years, Galileo had been fascinated by the simplicity and regularity
of pendulum motion. He was most impressed by the constancy of the pendulum’s
“period,” that is, the time the pendulum takes to complete its back-and-forth
cycle. If the pendulum’s swing is less than about 30 , its period is, to a good
approximation, dependent only on its length. (Another Galileo legend pictures
him as a nineteen-year-old boy in church, paying little attention to the service,
and timing with his pulse the swings of an oil lamp suspended on a wire from
a high ceiling.) In Padua, Galileo confirmed the constant-period rule with experiments,
and then uncovered some of the pendulum’s more subtle secrets.
In 1609, word came to Venice that spectacle makers in Holland had invented
an optical device—soon to be called a telescope—that brought distant objectsmuch closer. Galileo immediately saw a shining opportunity. If he could build a
prototype and demonstrate it to the Venetian authorities before Dutch entrepreneurs
arrived on the scene, unprecedented rewards would follow. He knew
enough about optics to guess that the Dutch design was a combination of a convex
and a concave lens, and he and his instrument maker had the exceptional
skill needed to grind the lenses. In twenty-four hours, according to Galileo’s own
account, he had a telescope of better quality than any produced by the Dutch
artisans. Galileo could have demanded, and no doubt received, a large sum for
his invention. But fame and influence meant more to him than money. In an
elaborate ceremony, he gave an eight-power telescope to Niccolo` Contarini, the
doge of Venice. Reston, in Galileo, paints this picture of the presentation of the
telescope: “a celebration of Venetian genius, complete with brocaded advance
men, distinguished heralds and secret operatives. Suddenly, the tube represented
the flowering of Paduan learning.” Galileo was granted a large bonus, his salary
was doubled, and he was reappointed to his faculty position for life.
Then Galileo turned his telescope to the sky, and made some momentous, and
as it turned out fateful, discoveries. During the next several years, he observed
the mountainous surface of the Moon, four of the moons of Jupiter, the phases
of Venus, the rings of Saturn (not quite resolved by his telescope), and sunspots.
In 1610, he published his observations in The Starry Messenger, which was an
immediate sensation, not only in Italy but throughout Europe.
But Galileo wanted more. He now contrived to return to Tuscany and Florence,
where he had spent most of his early life. The grand duke of Tuscany was the
young Cosimo de Medici, recently one of Galileo’s pupils. To further his cause,
Galileo dedicated The Starry Messenger to the grand duke and named the four
moons of Jupiter the Medicean satellites. The flattery had its intended effect.
Galileo soon accepted an astonishing offer from Florence: a salary equivalent to
that of the highest-paid court official, no lecturing duties—in fact, no duties of
any kind—and the title of chief mathematician and philosopher for the grand
duke of Tuscany. In Venice and Padua, Galileo left behind envy and bitterness.