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 The founder of Physics
was born in Pisa, February 15, 1564, three days before Michael
Angelo's death, and died in the year of Newton's
birth. His father, distinguished in the theory and practice of
music, was a poor descendant of the ancient and illustrious Florentine
family of Bonajuti, who, in the 14th century, had changed their
name for that of Galilei. He constructed mechanical toys for
his school-fellows; he threw himself eagerly into Greek and Latin
study; he inherited his father's skill in music; and he showed
remarkable aptitude for painting, to which two generations earlier
his life probably would have been devoted. Ariosto and Dante
remained his favorite poets throughout life. In his eighteenth
year he was sent to the University of Pisa, where he attended
lectures of the great Cesalpino, one of Harvey's forerunners.
Visitors to the cathedral are shown the bronze lamp which he
saw swinging, and of which he noticed that the swings, whether
through a large or small arc, took place in equal, or nearly
equal times. Of mathematics he knew nothing as yet, for his father,
wishing to concentrate him on medicine, had dissuaded him from
learning them. Yet he turned his discovery to account by constructing
a pendulum of proper length for measuring the speed and regularity
of the pulse: the first instrument perhaps ever made for precise
observation of phenomena in a living organism. Quite at the end
of his life, his thoughts turned again to the pendulum as the
best mode of measuring time with the exactness required in astronomy.
Galileo was not slow to find where his proper work lay. Viviani,
his disciple and biographer, tells us that underneath all his
studies of nature, life, and art, he felt, even before he knew,
that there lay the scientific foundation of the whole--the laws
of Geometry. From Ricci, a friend of his father, who taught mathematics
at the Grand-Ducal court, he received, at the age of 22, his
first lesson in Euclid. From Euclid he soon passed to Archimedes,
and fastened upon that part of his work in which the greatest
of geometers stood alone, the marvellous researches on the lever,
and on floating bodies. We note here, as in the case of Descartes
and Pappus, one of the bridges between ancient and modern science.
Galileo's first work was the construction of a balance for solving
in a simpler way Archimedes' problem of the crown of gold alloyed
with silver. This drew the attention of the Marquis Guid' Ubaldo
of Pesaro, a name well known in mathematical history, who urged
him to write, in 1588, his treatise on The Centre of Gravity
in Solids, and who procured the next year his election as
Mathematical Professor in Pisa. Here began his first series of
researches on motion, controlled by experiments on falling bodies
carried on from the Leaning Tower. Here, too, was his first crusade
against the decrepit philosophy of his time, in which Aristotle's
conjectures had been petrified into a creed, while of the open
mind and patient observation of the great master not a trace
was left.
After two years Pisa was too hot to hold him. But in 1592,
through the persistent help of Guid' Ubaldo, he became Professor
of Mathematics at Padua; and there, under the shelter of the
Venetian Republic, he spent the following eighteen years, and
did most of his constructive work. His lecture-hall had an audience
of two thousand, including strangers from every part of Europe.
His latest discoveries, and his suggestions for original researches,
were poured out to all comers ungrudgingly. The range of subjects
was wide. Besides the laws of equilibrium and motion, he dwelt
on the importance of measuring all natural forces, great or small,
abstruse or familiar, so as to bring them within the range of
geometry, and thus adapt them to the service of man. No one before
him had sought to measure heat with precision. His own thermometer,
though very imperfect, was the starting-point of others. It was
his disciple Torricelli who first measured the weight of the
atmosphere.
In astronomy it was well known that he took the Copernican
side. He held, with Bruno, that the universe was infinite, not
finite; and that the stars and planets were made of the same
substance as the world we live in. The use he made of the telescope--invented
in Holland in 1608, but greatly improved by himself in the following
year--showed facts that made this view far more probable. The
Dutch invention was for terrestrial purposes only. Galileo, not
neglecting these--for he won the favour of the Venetian Senate
by showing the distance at which an enemy's fleet could be descried--turned
his own more powerful instrument to the sky. He speedily discovered
Jupiter's four moons, the irregular surface of our own satellite,
the phases of Venus, certain bodies which he could not clearly
define surrounding Saturn, and the solar spots. The first of
these has been well described as a miniature Copernican system:
all of them showed the solar system to be far more complicated
than men thought. His resolution of the Milky Way into separate
stars gave another proof that our sun with its planets was but
an atom in a boundless universe.
The Venetian Senate at once raised Galileo's salary. But as
the Grand Duke offered him equal advantages in Florence, patriotism
turned the scale. He left Padua for Florence in 1610, and from
that time till his death he never knew peace. In the war between
Science and Theology he was eager for the fight; he had powerful
friends, and felt sure of victory. In 1611 he visited Rome, and
freely advocated the new conception of the universe. Systematic
clerical opposition now began. A letter from Galileo to Castelli,
in which he took the dangerous course of trying to harmonise
Science and Scripture, was laid before the Inquisition. Early
in 1616 the propositions of the sun's fixity and the earth's
diurnal motion were formally condemned; the work of Copernicus,
published seventy years before, was placed on the Index; and
a promise was extorted from Galileo not to defend his theory.
He remained silent for seven years. In 1623, when his friend
Maffeo Barbarini became Pope Urban VIII, he strove to get those
edicts reversed. In this he failed, yet still persisted in writing
his celebrated Dialogues on the Two Systems. This work
with much difficulty he obtained leave to print in 1632, on the
condition of inserting reservations dictated, it is thought,
by Urban himself, which disfigure the preface and the first section
of the work. But the dramatic form gave free play to the irony
of which Galileo was a master. Simplicius, the personage who
advocates obscurantism, was said, truly or not, to be Urban himself.
The book spread swiftly through Europe from south to north. It
was resolved that Galileo should be crushed. He was summoned
to Rome; and on the 22nd June 1633 he was forced to read and
sign a formal abjuration of his belief in the Copernican doctrine.
Tortured physically he was not; though had he refused, certain
death or imprisonment would have awaited him; and his principal
work was still unprinted. He was allowed to live in retirement
near Florence, all gatherings of friends being strictly forbidden.
His house was the Villa Martellini, at Arcetri, near the Convent
of St. Matthew, where his daughter, Sister Maria Celeste, was
a nun. It is sad to know that his daughter, whose touching letters
are preserved, and whose loving care had been his mainstay for
years, should have died soon after his return from Rome, worn
out by anxiety.
But his strenuous activity survived. His greatest book, the
Dialogues on the Two Sciences of Mechanics and Motion,
summing up his work at Pisa and Padua, was completed at this
time, and published in 1638 in Holland. He carried on a long
correspondence with the Dutch Government as to adopting observations
of Jupiter's satellites for determination of longitudes. His
last astronomical work was to discover the moon's libration.
Then sight failed him. Yet he still worked on, dictating to Viviani
and Torricelli important papers, amongst them one on the illumination
of the moon by earth light, and attempts to adapt the pendulum
to measurement of time. He was still full of schemes for new
inquiries when he was struck down by fever. He died on the 8th
of January 1642, in his 78th year.
Galileo did not demonstrate the earth's motion. What he did
was to found the science of Dynamic, which, in the hands of Newton
nearly a hundred years later, led to that demonstration. The
scientific study of motion, contrasted with that of equilibrium,
involves the new element of Time. Galileo defined uniform velocity
as that in which the spaces traversed were proportional to the
times of transit. Kepler had shown that a body acting under a
single impulse and unhindered, will move forever in a straight
line. But how was it with a body acted on by a continuous force,
as that of a body falling from rest under the influence of gravity?
That the velocity increased as the fall went was obvious; but
what was the law of the increase? His discovery of this law,
as Comte has said, is the crowning-point of his fame.
Galileo tells us that he put to himself as the simplist hypothesis
that equal increments of velocity took place in equal times.
As time is infinitely divisible, these increments are infinitely
small and numerous, and the problem was to sum them. It was a
problem of integration, though so simple as not to need a special
calculus. Galileo shows by a simple geometric process that, in
motion uniformly accelerated, the time occupied is equal to that
spent by a body moving uniformly with velocity equal to half
that attained by the accelerated body at the end of the period;
that the spaces traversed are as the squares of the time; and
as a corollary from this, that the spaces in each successive
interval are to one another as the series of the odd numbers.
In a further section of the work Galileo shows, with extreme
fulness, that a body, like a projectile, acted on simultaneously
by an impulse and by the continuous force of gravity, will move
in a parabola. The Second Law of Motion--that which Comte calls
the law of coexistence of movements--was clearly known to him.
Original as his discoveries in Dynamic were, those in Static
were hardly less important; and Lagrange, in the first section
of the Mécanique Analytique, fully appreciated
their importance. His work on the Utility of Mechanical Science
and the Instruments it employs, written, it is thought, in
1593, though published much later, contains on its first page
the distinct germ of the principle of Virtual Velocities, as
solving the apparent paradox, that the small weight at the long
arm of the lever could balance a large one. The velocity with
which the two arms tended to move was inversely proportionate
to the weights; and the case was therefore as though a man having
to carry a certain distance a load beyond his strength, took
many journeys annd conveyed a portion of it in each. The element
of time comes in.
Galileo tested his law of falling bodies partly by direct
observation, partly by comparing the spaces traversed in given
times upon inclined planes of the same altitude. The velocity,
identical at the end of the fall, admitted, in the earlier parts,
of more easy measurement than when the fall was vertical. It
may be said generally that the note of his whole work is mathematical
research controlling, and controlled by, observation of Nature.
For abstract mathematics he had little taste. "Philosophy,"
he says in his Saggiatore, "is written in the great
book of the Universe which lies always open. But we must first
understand the language and the character in which it is written.
That language is mathematics. Its characters are triangles, circles,
and other geometric figures, without which we cannot, humanely
speaking, understand the words, and wander aimlessly thhrough
a dark labyrinth."
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| This biography is
reprinted from The New Calendar of Great Men. Ed. Frederic
Harrison. London: Macmillan and Co., 1920. |
|
