213

G

Galilei, Galileo (1564–1642) Italian Mechanics, Astro-

nomy Born on February 15, 1564, in Pisa (now in

Italy), Galileo Galilei is remembered for his 1638 Dis-

corsi e dimostrazione matematiche intorno a due nuove

scienze (Dialogues on two new sciences) presenting a

new approach to the study of kinematics through a

combination of experiment and mathematical theory.

He formulated and verified the law of acceleration of

falling bodies , established that projectiles

follow parabolic paths, and was the first to notice that

the period of a pendulum is independent of the weight of

the bob. Although not the inventor of the telescope, he

was the first to develop a workable design of the device

that allowed him to make (outstanding) astronomical

observations. In particular, he accrued significant empiri-

cal evidence that supported the Copernican theory that

the planets travel around the Sun. His belief in this the-

ory brought him in conflict with the Roman Catholic

Church and led to his consequent trial and house arrest.

Galileo was sent by his parents to the University of

Pisa to study medicine at the age of 17, but this course

of study never appealed to him. He left the University

without obtaining a degree and began teaching mathe-

matics and mechanics in Sienna. In 1586 he wrote La

balancitta (The little balance), in which he described

the methods of A

RCHIMEDES OF

S

YRACUSE

(287–212

B

.

C

.

E

.) for finding the relative densities of substances

with a balance. This piece garnered him significant

attention in the scientific community, and in 1589 he

was appointed chair of mathematics at the University

of Pisa. He remained at this post for 3 years before

accepting the prestigious position as professor of math-

ematics at the University of Padua.

During his 18 years at Padua, Galileo developed his

theories of motion. Using inclined planes to slow the rate

of descent, Galileo observed that all objects fall at the

same rate of acceleration. From this, using mathematics

verified by experiment, he deduced his famous law that

the distance traveled by a falling object is proportional

to the square of the time of its fall. From this it follows

that objects tossed in the air move in parabolic arcs.

In 1609 Galileo received word that Dutch scholars

had invented a spyglass capable of magnifying images

of distant objects. Intrigued, Galileo set to constructing

his own version of the spyglass and eventually pro-

duced a piece (which he called a “perspicillum”) with a

magnification power of eight or nine—far superior to

the capabilities of the Flemish telescope. Galileo turned

his piece to the heavens and commenced a series of

remarkable astronomical discoveries.

In his 1610 book Sidereus nuncius (Starry messen-

ger), Galileo described the topography of the Moon,

established that the Milky Way is composed of stars,

and announced his discovery of four moons orbiting

Jupiter. For savvy political reasons, he named these

moons the “Medicean stars,” in honor of Cosimo de

Medici, the grand duke of Tuscany. This work garnered

Galileo considerable fame and, just one month after the

book was released, Galileo was appointed chief mathe-

matician at Pisa and “mathematician and philosopher”

to the grand duke of Tuscany.