GALILEO.

The Copernican theory, which Tycho had labored in vain to supersede,

was next received and supported by an Italian philosopher, whose name

and history are inseparably interwoven with the progress of astronomy.

That illustrious individual, Galileo Galilei, usually known by his

Christian name, was born at Pisa in 1564. His father, a Tuscan

nobleman of small fortune, caused him to be educated for the

profession of medicine at the university of his native city. While

studying there, he became deeply sensible of the absurdities of the

philosophy of Aristotle, as it had then come to be taught, and he

became its declared enemy. That spirit of observation for which he was

so distinguished was early developed. When only nineteen years old,

the swinging of a lamp suspended from the ceiling of the cathedral in

Pisa, led him to investigate the laws of the oscillation of the

pendulum, which he was the first to employ as a measure of time. He

left it incomplete, however, and it was brought to perfection by his

son, Vincenzo, and particularly by Hüygens, the latter of whom must be

regarded as the true inventor of the pendulum. About this period

Galileo devoted himself exclusively to mathematics and natural

science, and in 1586 was led to the invention of the hydrostatic

balance. In 1589, his distinction in the exact sciences gained for him

the chair of mathematics in his native university, where, immediately

on his installation, he began to assert the laws of nature against a

perverted philosophy. In the presence of numerous spectators, he

performed a series of experiments in the tower of the cathedral, to

show that weight has no influence on the velocity of falling bodies.

By this means he excited the opposition of the adherents of Aristotle

to such a degree, that, after two years, he was forced to resign his

professorship. Driven from Pisa, he retired into private life; but his

genius being appreciated in another part of Italy, he was, in 1592,

appointed professor of mathematics in Pudua. He lectured here with

unparalleled success. Scholars from the most distant regions of Europe

crowded round him. He delivered his lectures in the Italian language

instead of Latin, which was considered a daring innovation.

During eighteen years which he spent at Padua, he made many

discoveries in natural philosophy, which he introduced into his

lectures, without regard to their inconsistency with the doctrines

previously taught. Among these may be mentioned his discovery of the

rate of descent in falling bodies; certain improvements on the

thermometer; some interesting observations on the magnet; and a number

of experiments relative to the floating and sinking of solid bodies in

water. In 1609, hearing that one Jansen, a Dutchman, had made an

instrument by which distant objects were made to appear near, Galileo,

whose mind was prepared for the discovery, instantly conceived on what

principle it was constructed, and, without losing a day, he fashioned

a similar instrument with many improvments: such was the origin of the

telescope, the most interesting of all instruments connected with

science.

Turning his optical tube towards the heavens, Galileo perceived the

moon to be a body of uneven surface, the elevations of which he

computed by their shadows; and the sun to be occasionally spotted; and

from the regular advance from east to west of these spots, he inferred

the rotation of the sun, and the inclination of its axis to the plane

of the ecliptic. From a particular nebula, which his rude instrument

enabled him to resolve into individual stars, he even conjectured,

what Lord Rosse has but recently proved, that the whole Milky Way was

but a vast assemblage of stars and systems. He discovered that the

planet Venus waxed and waned like the moon, that Saturn had something

like wings by its sides (afterwards found to be a ring), and that

Jupiter was surrounded by four satellites. It is now altogether

impossible to imagine the wonder and delight with which these

discoveries must have filled the mind of a philosopher like Galileo,

who had perhaps long surmised that all was not as it seemed in the

heavens, but despaired of ever being able to penetrate the mystery. In

the year 1611, while entering upon his investigations, he was induced,

by the invitation of his prince, the Grand Duke of Tuscany, to return

to Pisa, and resume the chair of mathematics there, with a large

salary. It was consequently at that city that he first gave his

discoveries to the world. That persecution which had only been

suspended by accident in the case of Copernicus, now fell with full

weight on the head of the Italian philosopher. Having openly declared,

in a work which he published, that his discoveries proved the truth of

the Copernican theory, he was denounced by the clergy as a heretic,

and obliged, in 1615, to proceed to Rome, and appear before the court

of Inquisition, who obliged him to promise that he would never more

broach such dangerous doctrines. It has been stated, but is not quite

certain, that he was on this occasion imprisoned by the Inquisition

for five months, and that he would have suffered still more severely

if the Grand Duke had not interceded for him.

For several years he observed the silence enjoined upon him, but

continued to pursue the study of the true theory of the heavens.

Panting to make known to the world a complete account of the system of

Copernicus, yet dreading the prejudices of his enemies, he fell upon

the expedient of writing a work, in which, without giving his own

opinion, he introduces three persons in a dialogue, of whom the first

defends the Copernican system, the second the Ptolemæan (or that of

Aristotle), and the third weighs the reasons of both in such a way,

that the subject seems problematical, though it is impossible to

mistake the preponderance of arguments in favor of Copernicus. With

this great work, which is still held in reverence, Galileo went to

Rome in 1630, in the sixty-sixth year of his age, and, by an

extraordinary stretch of favor, received permission to print it.

Scarcely had it appeared at Rome and Florence, when it was attacked by

the disciples of Aristotle, and most violently of all by the teacher

of philosophy at Pisa. A congregation of cardinals, monks, and

mathematicians, was appointed to examine his work, which they

unhesitatingly condemned as highly dangerous, and summoned him before

the tribunal of the Inquisition. This blow fell heavily on the head of

Galileo, now an old man, and left defenseless by the death of his

friend and patron, Cosmo II. He was compelled to go to Rome in the

winter of 1633, and was immediately immured in a cell in one of the

prisons of the Inquisition. There he remained for several months,

when, being brought before an assembly of his judges, he was condemned

to renounce, kneeling before them, with his hand upon the gospels,

what were called the ‘sinful and detestable errors and heresies’ which

he had maintained. The firmness of Galileo gave way at this critical

moment of his life: he pronounced the recantation. But at the moment

he rose, indignant at having sworn in violation of his conviction, he

exclaimed, stamping his foot, ‘_E pur si muove!_’――(‘It still moves!’)

Upon this dreadful relapse into heresy, he was sentenced to

imprisonment in the Inquisition for life, and every week for three

years was to repeat the seven penitential psalms; his ‘Dialogues’ were

also prohibited, and his system utterly condemned. Although Galileo

was in this manner sentenced to confinement, it appeared to those who

judged him that he would not be able, from his age, to endure such a

severe punishment, and they mercifully banished him to a particular

spot near Florence.

Here Galileo lived for several years, employing his time in the study

of mechanics and other branches of natural philosophy. The results are

found in two important works on the laws of motion, the foundation of

the present system of physics and astronomy. At the same time he tried

to make use of Jupiter’s satellites for the calculation of longitudes;

and though he brought nothing to perfection in this branch, he was the

first who reflected systematically on such a method of fixing

geographical longitudes. He was at this time afflicted with a disease

in his eyes, one of which was wholly blind, and the other almost

useless, when, in 1637, he discovered the libration of the moon.

Blindness, deafness, want of sleep, and pain in his limbs, united to

embitter his declining years; still his mind was active. ‘In my

darkness,’ he writes in the year 1638, ‘I muse now upon this object of

nature, and now upon that, and find it impossible to soothe my

restless head, however much I wish it. This perpetual action of mind

deprives me almost wholly of sleep.’ In this condition, and affected

by a slowly-consuming fever, he expired in January, 1642, in the

seventy-eighth year of his age. His relics were deposited in the

church of Santa Croce, at Florence, where posterity did justice to his

memory by erecting a splendid monument in 1737.

Galileo is represented by his biographers as of diminutive stature,

but strong and healthy, of agreeable countenance, and lively

conversation and manner. He preferred living in the country, where his

relaxations consisted in the cultivation of his garden, and in the

company and conversation of his friends. He loved music, drawing, and

poetry; and is said to have been so fond of Ariosto, that he knew the

whole of the ‘Orlando’ by heart. He had few books; ‘the best book,’ he

said, ‘is nature.’ A complete edition of his works, in thirteen

volumes, appeared at Milan in 1803, the style of which is natural and

fluent, so elegant and pure, that it has been held up by competent

judges as a model of classical Italian. ‘Altogether,’ says Professor

Playfair, ‘Galileo is one of those to whom human knowledge is under

the greatest obligation. His discoveries in the theory of motion, in

the laws of the descent of heavy bodies, and in the motion of

projectiles, laid the foundation of all the great improvements which

have since been made by the application of mathematics to natural

philosophy. If to these we add the invention of the telescope, the

discoveries made by that instrument, the confirmation of the

Copernican system which these discoveries afforded, and lastly, the

wit and argument with which he combated and exposed the prejudice and

presumption of the schools, we must admit that the history of human

knowledge contains few greater names than that of Galileo.’