In the later Middle Ages, learned study of the natural world, usually termed “natural
philosophy,” had gone on primarily in Europe’s universities, where it was seen as an appropriate
part of understanding the glory of God. Such study revolved around ancient
Greek ideas and texts, particularly those of Aristotle and Ptolemy. Aristotle (384–322
bce ) viewed the cosmos as centered on a motionless earth, with the planets (including
the moon and sun) revolving around it in fi xed spheres made up of a crystalline
substance, and the fi xed stars at its outer perimeter. The planets moved, he thought,
in exactly circular orbits at a uniform speed, and were perfectly round bodies made of
ether, a substance completely different from the four terrestrial elements – earth, air,
fi re, and water. Above the moon – the heavenly body closest to earth – the cosmos was
changeless, so that objects that did change in the skies, such as comets and meteors,
must be closer than the moon. Things on earth did change, and each element had a
tendency to move in a specifi c direction; things made primarily of the element earth
tended to move toward the center of the earth, while water fl owed sideways around
the earth and air went upward. The earth was round, the perfectly spherical center of
a perfectly spherical cosmos.
There were problems with Aristotle’s view. For one, it did not fi t with the motions
of the planets observable from earth – the planets often appear to move backwards
or reverse direction – but this was solved in the second century by Ptolemy ( c . 100–
c . 165 ce ), a Greek astronomer working at Alexandria. Ptolemy held that the moon,
sun, planets, and stars move around the motionless earth at various rates of speed in
spiral-like paths he called epicycles. Based on observation, he calculated the epicycles
of the major heavenly bodies, and the Ptolemaic system gained wide and long-lasting
acceptance.
The rediscovery of Greek writings other than those of Aristotle and Ptolemy led
scholars in a different direction. In the fi fteenth and sixteenth centuries, the works
of Pythagoras ( c . 582–c . 496 bce ), Plato ( c . 428–c . 348 bce ), and Archimedes ( c . 287–
c . 212 bce ), were copied, translated, and ultimately printed. All of these ancient writers
emphasized the importance of mathematics as the underlying structure of the universe,
an idea that was echoed by their later admirers. Johannes Kepler (1571–1630), a
German astronomer who calculated the laws of planetary motion, wrote: “Geometry,
which before the origin of things was coeternal with the divine mind and is God himself
… supplied God with patterns for the creation of the world.” 2 Kepler and other
scholars saw the mathematical patterns of the universe as a mystical harmony, created
by God and ultimately understandable to humans.
Among the ancient texts rediscovered in the fi fteenth century was a body of writings
attributed to Hermes Trismegistus, a god-like Egyptian sage thought to have lived
at the time of Moses. These Hermetic writings – now known to have been written in
the second and third centuries ce – were revered as ancient wisdom, and offered suggestions
on how to exploit the hidden divine powers of minerals, plants, the planets,
and other natural objects. Through processes of distillation, heating, and sublimation
(cooking something to a gaseous state and then resolidifying it), these hidden powers
could be tapped to transform lead into gold or cure disease and prolong life, practices
usually termed alchemy.
The Swiss physician Theophrastus Bombastus von Hohenheim, who called himself
Paracelsus (1493?–1541), fully embraced the Hermetic tradition, as did many other
scientists, who sometimes linked Hermeticism with Christian ideas about the power
of angels. Paracelsus rejected the Aristotelian elements and the Galenic notion that
disease is caused by an imbalance of bodily humors, and introduced the use of drugs
made from small doses of purifi ed minerals, especially sulfur, antinomy, and mercury.
Hoping to fi nd one powerful agent – often called the “philosopher’s stone,” or the
“elixir of life” – that was capable of healing all illnesses and transforming all less perfect
substances into more perfect ones, Paracelsus and other alchemists experimented
with ways to extract pure elements (termed magisteria ) and divine essences (termed
arcana ). With its peculiar properties as a metal that is liquid at normal room temperature,
mercury was often part of alchemical theories, as was gold distilled in various
liquids so that it was drinkable ( aurum potabile ).
Alchemists such as Paracelsus were rooted in ancient texts, but they were innovative
in their methods, advocating experimentation as the best way to discover the hidden
properties of various substances. They were often the earliest to make extensive use of
what was later called the “scientifi c method,” in which a hypothesis to explain a phenomenon
is developed, tested, the results recorded and measured, and the hypothesis
confi rmed, rejected, or modifi ed. They invented equipment still used in laboratories
today, such as beakers and balance scales, and discovered new ways of producing chemical
changes, such as the application of acids and alcohols.
The development of the scientifi c method is often associated with the English philosopher
and statesman Francis Bacon (1561–1626), who took his inspiration and procedures
straight from alchemy. In The Advancement of Learning (1605) and Novum
organum (New Instrument, 1620), Bacon rejected earlier claims of knowledge as based
on faulty reasoning, and called for natural philosophy that began with the empirical
observation of many similar phenomena. Those studying the phenomena would then
use their powers of reason to propose a generalized explanation or hypothesis for the
phenomena, a process called induction. This generalization would then be tested with
further empirical and inductive inquiry. Like any good alchemist, Bacon was a fi rm
believer in the practical value of science in promoting human progress and greater
control of nature. He called for national support for scientifi c investigations, which led
the founders of the English Royal Society in 1660 to see him as an inspiration.
The nineteenth-century historians of science who developed the idea of a “Scientifi c
Revolution” often tried to ignore the alchemical and magical interests of the thinkers
they championed, but most major fi gures in the Scientifi c Revolution believed fi rmly
in alchemy, astrology, and other examples of what are now often judged to be fringe
occult beliefs. In his work on the motion of the planets, Kepler hoped to discover the
mystical proportions underlying the universe and an explanation for how the heavenly
bodies infl uenced human life. The Danish astronomer Tycho Brahe (1546–1601)
constructed an advanced observatory and kept careful records of the skies, and also
had an alchemical laboratory with multiple ovens for cooking and distilling plants
and minerals to gain their spiritual essence. The Irish chemist Robert Boyle (1627–91)
developed laws about the behavior of gases and disproved the theory that air, earth,
fi re, and water were the basic elements, asserting instead that everything was made of
very small particles in motion, which he called “corpuscles.” In long laboratory reports
written in code, Boyle also reported to have witnessed elixirs that turned lead into gold
and gold into lead.
By the eighteenth century, those who experimented on the natural world tended
to defi ne forces or substances they could not see in material rather than spiritual or
mystical terms. George Ernst Stahl (1660–1734), a German chemist and physician,
proposed that combustion and other processes resulted in the release and absorption
of a substance he called phlogiston. The phlogiston theory led other chemists
to study gases – what they called “airs” – and in the middle of the eighteenth century
carbon dioxide and hydrogen were both identifi ed as substances different than
the air that surrounds us. In the early 1770s, the Swedish apothecary Carl Wilhelm
Scheele (1742–86) and the English cleric and theologian Joseph Priestley (1733–1804)
both discovered an air in which substances burned more easily. Viewing his discovery
within the context of the phlogiston theory, Priestley called it “dephlogisticated
air.”
The French chemist Antoine Lavoisier (1743–94) performed similar experiments,
but interpreted the results differently. He recognized that the same substance allows
for combustion, the action of acids, and respiration in living things, and called
this substance “oxygen.” Lavoisier’s oxygen theory came to replace the phlogiston
theory, particularly as Lavoisier made it part of a radically new way of discussing
chemical compounds and processes in his Elementary Treatise on Chemistry (1789),
the first modern textbook on chemistry. Like Bacon, Lavoisier regarded science as
a way of providing solutions to real-world problems, and he experimented on crop
rotation, the quality of drinking water, the military and scientific use of balloons,
and the production of gunpowder. He also proposed reforms for the French economy
and prison system, but his involvement in tax collection ultimately outweighed
his contributions and he was sent to the guillotine during the French Revolution.
World History
