Galileo in Padua
His
residence at Padua, which extended over a period of eighteen
years, from 1592 to 1610, was a course of uninterrupted
prosperity. His appointment was three times renewed, on each
occasion with the expressions of the highest esteem on the
part of the governing body, and his yearly salary was
progressively raised from 180 to 1000 forms. His lectures were
attended by persons of the highest distinction from all parts
of Europe, and such was the charm of his demonstrations that a
hall capable of containing 2000 people had eventually to be
assigned for the accommodation of the overflowing audiences
which they attracted. His invention of the proportional
compass or sector—an implement still used in geometrical
drawing—dates from 5597; and about the same time he
constructed the first thermostat, consisting of a bull,
and tube filled with air and
water, and terminating in a vessel of water. In this
instrument the results of varying atmospheric pressure were
not distinguishable from the expansive and contractive effects
of heat and cold, and it became an efficient measure of
temperature only when Rinieri, in 1646, introduced the
improvement of hermetically sealing the liquid in glass.
Galileo and the thermometer
The
substitution, in 1670, of mercury for water completed the
modern thermometer.
Galileo seems, at
an early period of his life, to have adopted the Copernican
theory of the solar system, and was deterred from avowing his
opinions - as is proved by his letter to Kepler of August 4,
1597, by the fear of ridicule rather than of persecution. The
appearance, in September 1604, of a new star in the
constellation Serpentarius afforded him indeed an opportunity,
of which he eagerly availed himself, for making an onslaught
upon the Aristotelian axiom of the incorruptibility of the
heavens; but he continued to conform his public teachings in
the main to Ptolemaic principles, until the discovery of a
novel and potent implement of research in the shape of the
telescope (q.v.) placed at his command startling and hitherto
unsuspected evidence as to the constitution and mutual
relations of the heavenly bodies.
Galileo and the telescope
Galileo was
not the original inventor of the telescope. That honor must be
assigned to Johannes Lippershey, an obscure optician of
Middleburg, who, on the 2nd of October 2608, petitioned the
states-general of the Low Countries for exclusive rights in
the manufacture of an instrument for increasing the apparent
size of remote objects. A rumor of the new invention, which
reached Venice in June 2609, sufficed to set Galileo on the
track; and after one night’s profound meditation on the
principles of refraction, he succeeded in producing a
telescope of threefold magnifying power. Upon this first
attempt he rapidly improved, until he attained to a power of
thirty-two, and his instruments, of which he manufactured
hundreds with his own hands, were soon in request in every
part of Europe. Two lenses only, a plane convex and a
piano-concave were needed for the composition of each, and
this simple principle is that still employed in the
construction of opera-glasses. Galileo’s direction of his
new instrument to the heavens formed an era in the history of
astronomy. Discoveries followed upon it with astounding
rapidity and in bewildering variety.
Galileo's observations with
the telescope
The Sidereus
Nuncius, published at Venice early in 1610, contained the
first-fruits of the new mode of investigation, which were
sufficient to excite learned amazement on both sides of the
Alps. The mountainous configuration of the moon’s surface
was there first described, and the so-called
phosphorescence “of
the dark portion of our satellite attributed to its true cause,
namely, illumination by sunlight reflected from the earth. All
the time-worn fables and conjectures regarding the composition
of the Milky Way were at once dissipated by the simple
statement that to the eye, reinforced by the telescope, it
appeared as a congeries of lesser stars, while the great
nebulae were equally declared to be resolvable into similar
elements. But the discovery which was at once perceived to be
most important in itself, and most revolutionary in its
effects, was that of Jupiter’s satellites, first seen by
Galileo on the 7th of January 1610, and by him named Sidera
Medicea, in honor of the grand-duke of Tuscany, Cosmo II.,
who had been his pupil, and was about to become his
employer.
An
illustration is, with the general run of mankind, more
powerful to convince than an argument; and the cogency of the
visible plea for the Copernican theory offered by the
miniature system, then first disclosed to view, was
recognizable in the triumph of its advocates as well as in the
increased acrimony of its opponents.
Galileo in Florence
In
September 1610 Galileo finally abandoned Padua for Florence.
His researches with the telescope had been rewarded.
The telescope was invented by Demiscianus, an eminent Greek
scholar, at the request of Prince Cesi, president of the
Lyncean Academy. It was used by Galileo as early as 1612, but
was not introduced into England until much later. In 1655 the
word telescope was inserted and explained in Bagwell’s Mysteries
of Astronomy, trunk or cylander being the terms until then
ordinarily employed.
By the
Venetian senate, he was appointed for life to his
professorship, at an unprecedented high salary. His discovery
of the “Medicean Stars” was acknowledged by his
nomination (July 12, 1610) as philosopher and mathematician
extraordinary to the grand-duke of Tuscany. The emoluments of
this office, which involved no duties save that of continuing
his scientific labors, were fixed at 1000 scudi; and it
was the desire of increased leisure, rather than the
promptings of local patriotism, which induced him to accept an
offer the original suggestion of which had indeed come from
himself. Before the close of 1610 the memorable cycle of
discoveries begun in the previous year was completed by the
observation, as it appeared to Galileo, of the triple form of
Saturn (the ring-formation was first recognized by Christiaan
Huygens in 1655), of the phases of Venus, and of the spots
upon the sun. As regards sun-spots, however, Johann Fabricius
of Osteel in Friesland can claim priority of publication, if
not of actual detection.
Galileo's Letters on the
Solar Spots
In the
spring of 1611 Galileo visited Rome, and exhibited in the
gardens of the Quirinal Palace the telescopic wonders of the
heavens to the most eminent personages at the pontifical
court. Encouraged by the flattering reception accorded to him,
he ventured, in his Letters on the Solar Spots, printed at
Rome in 1613, to take up a more decided position towards that
doctrine on the establishment of which, as he avowed in a
letter to Belisario Vinta, secretary to the grand-duke, “all
his life and being henceforward depended.” Even in the time
of Copernicus some well-meaning persons, especially those of
the reformed persuasion, had suspected a discrepancy between
the new view of the solar system and certain passages of
Scripture, a suspicion strengthened by the anti Christian
inferences drawn from it by Giordano Brunc; but the question
was never formally debated until Galileo’s brilliant
disclosures, enhanced by his formidable dialectic and
enthusiastic zeal, irresistibly challenged for it the
attention of the authorities.