52 The Poetry of Physics and The Physics of Poetry
Galileo’s experiments and observations lead him to formulate the
parabolic law of motion of a projectile in the Earth’s gravitational field.
These studies also lead him very nearly to a formulation of inertia, the
concept that a body remains at rest or in uniform straight-line motion
unless a force acts upon it. This concept, which plays such a central
role in Newton’s formulation of classical mechanics, was not clearly
enunciated until Descartes. Another of the important contributions
made by Galileo, as is exemplified by his work on projectiles, is the
incorporation of mathematics into his description of nature. There is no
doubt he was influenced by Euclid and Archimedes when he wrote,
“trying to deal with physical problems without geometry is attempting
the impossible” or “the book of Nature is written in mathematical
characters.”
Perhaps Galileo’s most fascinating experimental work was done with
his invention of the telescope. His results established the Copernican
system on a firm experimental basis as he laid to rest the Aristotelian
concept that the heavens are unchanging and made of the fragile
substance aether. With the appearance of a new star in 1572 and the new
comet of 1577, came the first empirical evidence against the concept of
the immutable heavens. These two events carefully recorded by Brahe
were not enough to change Brahe’s attitude or that of the other scholars
towards Aristotle’s physics. More evidence was required and this was
provided with Galileo’s telescopic observations of mountains on the
Moon like those found on Earth and his observation of the appearance,
movement and disappearance of sunspots (which we have since
discovered are electrical storms on the surface of the Sun). Finally, his
discovery of the moons of Jupiter and the rings of Saturn showed that the
Earth was not the only planet in the solar system with a satellite, which
had been used as an argument against the Copernican scheme.
Kepler’s Three Laws of Planetary Motion
At the same time Galileo was establishing the Copernican system
with his telescopic discoveries, Johannes Kepler also a supporter of
Copernicus, was working on the mathematical problem of finding the
actual orbits of the planets about the Sun. Kepler made use of the
enormous amount of data collected by Tycho Brahe for whom he worked
during the last days of the Dane’s life. Instead of trying to describe the
orbits as superpositions of circles or epicycles, Kepler tried to fit the