The Science Book

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CONTRIBUTORS PENNY JOHNSON

ADAM HART-DAVIS, CONSULTANT EDITOR Penny Johnson started out as an aeronautical
engineer, working on military aircraft for 10 years
Adam Hart-Davis trained as a chemist at the universities of before becoming a science teacher, then a publisher
Oxford and York, and Alberta, Canada. He spent five years producing science courses for schools. Penny has been
editing science books, and has been making television and a full-time educational writer for over 10 years.
radio programs about science, technology, mathematics, and
history, as producer and host, for 30 years. He has written 30 DOUGLAS PALMER
books on science, technology, and history.
Douglas Palmer, a science writer based in Cambridge,
JOHN FARNDON Britain, has published more than 20 books in the last
14 years—most recently an app (NHM Evolution) for
John Farndon is a science writer whose books have been the Natural History Museum, London, and DK’s WOW
short-listed for the Royal Society junior science book prize four Dinosaur book for children. He is also a lecturer for the
times and for the Society of Authors Education Award. His University of Cambridge Institute of Continuing Education.
books include The Great Scientists and The Oceans Atlas. He
was a contributor to DK’s Science and Science Year by Year. STEVE PARKER

DAN GREEN Steve Parker is a writer and editor of more than 300
information books specializing in science, particularly
Dan Green is an author and science writer. He has an MA biology and allied life sciences. He holds a BSc in Zoology,
in Natural Sciences from Cambridge University and has is a Senior Scientific Fellow of the Zoological Society of
written over 40 titles. He received two separate nominations London, and has authored titles for a range of ages and
for the Royal Society Young People’s Book Prize 2013 and publishers. Steve has received numerous awards, most
his Basher Science series has sold over 2 million copies. recently the 2013 UK School Library Association
Information Book Award for Science Crazy.
DEREK HARVEY
GILES SPARROW
Derek Harvey is a naturalist with a particular interest in
evolutionary biology, and a writer for titles that include DK’s Giles Sparrow studied astronomy at University College
Science and The Natural History Book. He studied Zoology at London and Science Communication at Imperial College,
the University of Liverpool, taught a generation of biologists, London, and is a best-selling science and astronomy author.
and has led expeditions to Costa Rica and Madagascar. His books include Cosmos, Spaceflight, The Universe in
100 Key Discoveries, and Physics in Minutes, as well as
contributions to DK books such as Universe and Space.

CONTENTS

10 INTRODUCTION SCIENTIFIC
REVOLUTION
THE BEGINNING
OF SCIENCE 1400–1700

600 BCE–1400 CE 34 At the center of
everything is the Sun
20 Eclipses of the Sun can Nicolaus Copernicus
be predicted
Thales of Miletus 40 The orbit of every planet
is an ellipse
21 Now hear the fourfold Johannes Kepler
roots of everything
Empedocles 42 A falling body
accelerates uniformly
22 Measuring the Galileo Galilei
circumference of Earth
Eratosthenes 44 The globe of the Earth
is a magnet
23 The human is related William Gilbert
to the lower beings
Al-Tusi 45 Not by arguing, but by
trying Francis Bacon

46 Touching the spring of 55 Layers of rock form on top
the air Robert Boyle of one another
Nicolas Steno
50 Is light a particle
or a wave? 56 Microscopic observations
Christiaan Huygens of animalcules
Antonie van Leeuwenhoek
24 A floating object displaces 52 The first observation of
58 Measuring the speed
its own volume in liquid a transit of Venus of light
Ole Rømer
Archimedes Jeremiah Horrocks
60 One species never springs
26 The Sun is like fire, the 53 Organisms develop in from the seed of another
Moon is like water a series of steps John Ray
Zhang Heng Jan Swammerdam
62 Gravity affects everything
28 Light travels in straight 54 All living things are in the universe
lines into our eyes composed of cells Isaac Newton
Alhazen Robert Hooke

EXPANDING 96 No vestige of a beginning 115 Mapping the rocks of
HORIZONS and no prospect of an end a nation
James Hutton William Smith
1700–1800
102 The attraction of mountains 116 She knows to what tribe
74 Nature does not proceed Nevil Maskelyne the bones belong
by leaps and bounds Mary Anning
Carl Linnaeus 104 The mystery of nature
in the structure and 118 The inheritance of
76 The heat that disappears fertilization of flowers acquired characteristics
in the conversion of water Christian Sprengel Jean-Baptiste Lamarck
into vapor is not lost
Joseph Black 105 Elements always combine 119 Every chemical compound
the same way has two parts
Joseph Proust Jöns Jakob Berzelius

78 Inflammable air A CENTURY 120 The electric conflict is
Henry Cavendish OF PROGRESS not restricted to the
conducting wire
80 Winds, as they come 1800–1900 Hans Christian Ørsted
nearer the equator,
become more easterly 110 The experiments may 121 One day, sir, you may
George Hadley be repeated with great tax it
ease when the Sun shines Michael Faraday
81 A strong current comes Thomas Young
out of the Gulf of Florida 122 Heat penetrates every
Benjamin Franklin 112 Ascertaining the relative substance in the universe
weights of ultimate particles Joseph Fourier
82 Dephlogisticated air John Dalton
Joseph Priestley 124 The artificial production
114 The chemical effects of organic substances
84 In nature, nothing is produced by electricity from inorganic substances
created, nothing is lost, Humphry Davy Friedrich Wöhler
everything changes
Antoine Lavoisier 126 Winds never blow in
a straight line
85 The mass of a plant comes Gaspard-Gustave de Coriolis
from the air
Jan Ingenhousz 127 On the colored light of
the binary stars
86 Discovering new planets Christian Doppler
William Herschel
128 The glacier was God’s
88 The diminution of the great plough
velocity of light Louis Agassiz
John Michell
130 Nature can be represented
90 Setting the electric fluid as one great whole
in motion Alessandro Volta Alexander von Humboldt

136 Light travels more slowly 226 Particles have wavelike
in water than in air properties
Léon Foucault Erwin Schrödinger

138 Living force may be 234 Uncertainty is inevitable
converted into heat Werner Heisenberg
James Joule
236 The universe is big…
139 Statistical analysis of 186 Rays were coming from and getting bigger
molecular movement the tube Edwin Hubble
Ludwig Boltzmann Wilhelm Röntgen
242 The radius of space began
140 Plastic is not what I 188 Seeing into the Earth at zero
meant to invent Richard Dixon Oldham Georges Lemaître
Leo Baekeland
190 Radiation is an atomic 246 Every particle of matter
142 I have called this principle property of the elements has an antimatter
natural selection Marie Curie counterpart
Charles Darwin Paul Dirac
196 A contagious living fluid
150 Forecasting the weather Martinus Beijerinck 248 There is an upper
Robert FitzRoy limit beyond which a
collapsing stellar core
156 Omne vivum ex vivo— A PARADIGM SHIFT becomes unstable
all life from life Subrahmanyan
Louis Pasteur 1900–1945 Chandrasekhar

160 One of the snakes 202 Quanta are discrete 249 Life itself is a process
grabbed its own tail packets of energy of obtaining knowledge
August Kekulé Max Planck Konrad Lorenz

166 The definitely expressed 206 Now I know what the
average proportion of atom looks like
three to one Ernest Rutherford
Gregor Mendel

172 An evolutionary link 214 Gravity is a distortion
between birds and in the space-time
dinosaurs continuum
Thomas Henry Huxley Albert Einstein

174 An apparent periodicity 222 Earth’s drifting continents
of properties are giant pieces in an
Dmitri Mendeleev ever-changing jigsaw
Alfred Wegener
180 Light and magnetism
are affectations of the 224 Chromosomes play a role
same substance in heredity
James Clerk Maxwell Thomas Hunt Morgan

250 95 percent of the 286 A perfect game of 315 Earth and all its life forms
universe is missing tic-tac-toe make up a single living
Fritz Zwicky Donald Michie organism called Gaia
James Lovelock
252 A universal computing 292 The unity of
machine fundamental forces 316 A cloud is made of billows
Alan Turing Sheldon Glashow upon billows
Benoît Mandelbrot
254 The nature of the 294 We are the cause of
chemical bond global warming 317 A quantum model
Linus Pauling Charles Keeling of computing
Yuri Manin
260 An awesome power is 296 The butterfly effect
locked inside the nucleus Edward Lorenz 318 Genes can move from
of an atom species to species
J. Robert Oppenheimer 298 A vacuum is not Michael Syvanen
exactly nothing
FUNDAMENTAL Peter Higgs 320 The soccer ball can
BUILDING BLOCKS withstand a lot
300 Symbiosis is everywhere of pressure
1945–PRESENT Lynn Margulis Harry Kroto

270 We are made of stardust 302 Quarks come in threes 322 Insert genes into humans
Fred Hoyle Murray Gell-Mann to cure disease
William French Anderson
271 Jumping genes 308 A theory of everything?
Barbara McClintock Gabriele Veneziano 324 Designing new life forms
on a computer screen
272 The strange theory of 314 Black holes evaporate Craig Venter
light and matter Stephen Hawking
Richard Feynman 326 A new law of nature
Ian Wilmut
274 Life is not a miracle
Harold Urey and 327 Worlds beyond the
Stanley Miller solar system
Geoffrey Marcy
276 We wish to suggest
a structure for the salt 328 DIRECTORY
of deoxyribose nucleic
acid (DNA) 340 GLOSSARY
James Watson and
Francis Crick 344 INDEX

284 Everything that can 352 ACKNOWLEDGMENTS
happen happens
Hugh Everett III

INTRODU

CTION

12 INTRODUCTION

Science is an ongoing search to be reinforced by the French comets reported in 1531 and 1607,
for truth—a perpetual philosopher René Descartes, and suggested that all three were
struggle to discover how the Bacon’s scientific method requires the same object, in orbit around the
universe works that goes back to scientists to make observations, Sun. He predicted that it would
the earliest civilizations. Driven form a theory to explain what is return in 1758, and he was right,
by human curiosity, it has relied going on, and then conduct an though only just—it was spotted on
on reasoning, observation, and experiment to see whether the December 25. Today, the comet is
experiment. The best known of theory works. If it seems to be true, known as Halley’s Comet. Since
the ancient Greek philosophers, then the results may be sent out astronomers are rarely able to
Aristotle, wrote widely on scientific for peer review, in which people perform experiments, evidence
subjects and laid foundations for working in the same or a similar can come only from observation.
much of the work that has followed. field are invited to pick holes in the
He was a good observer of nature, argument, and so falsify the theory, Experiments may test a theory,
but he relied entirely on thought and or to repeat the experiment to make or be purely speculative. When the
argument, and did no experiments. sure that the results are correct. New Zealand-born physicist Ernest
As a result, he got a number of Rutherford watched his students
things wrong. He asserted that big Making a testable hypothesis fire alpha particles at gold leaf in
objects fall faster than little ones, for or a prediction is always useful. a search for small deflections, he
example, and that if one object had English astronomer Edmond Halley, suggested putting the detector
twice the weight of another, it observing the comet of 1682, beside the source, and to their
would fall twice as fast. Although realized that it was similar to astonishment some of the alpha
this is mistaken, no one doubted it particles bounced back off the
until the Italian astronomer Galileo All truths are easy to paper-thin foil. Rutherford said it
Galilei disproved the idea in 1590. understand once they are was as though an artillery shell had
While it may seem obvious today discovered; the point is to bounced back off tissue paper—
that a good scientist must rely on and this led him to a new idea
empirical evidence, this was not discover them. about the structure of the atom.
always apparent. Galileo Galilei
An experiment is all the more
The scientific method compelling if the scientist, while
A logical system for the scientific proposing a new mechanism or
process was first put forward by the theory, can make a prediction about
English philosopher Francis Bacon the outcome. If the experiment
in the early 17th century. Building produces the predicted result, the
on the work of the Arab scientist scientist then has supporting
Alhazen 600 years earlier, and soon evidence for the theory. Even
so, science can never prove
that a theory is correct; as the

INTRODUCTION 13

20th-century philosopher of science Niels Bohr in the 1920s, which apparently to show he was
Karl Popper pointed out, it can only depended on the discovery of the immortal—and as a result we
disprove things. Every experiment electron in 1897, which in turn remember him to this day.
that gives predicted answers is depended on the discovery of
supporting evidence, but one cathode rays in 1869. Those could Stargazers
experiment that fails may bring not have been found without the Meanwhile, in India, China, and
an entire theory crashing down. vacuum pump and, in 1799, the the Mediterranean, people tried to
invention of the battery—and so the make sense of the movements of
Over the centuries, long-held chain goes back through decades the heavenly bodies. They made
concepts such as a geocentric and centuries. The great English star maps—partly as navigational
universe, the four bodily humors, physicist Isaac Newton famously aids—and named stars and groups
the fire-element phlogiston, and a said, “If I have seen further, it is of stars. They also noted that a
mysterious medium called ether by standing on the shoulders of few traced irregular paths when
have all been disproved and giants.” He meant primarily Galileo, viewed against the “fixed stars.”
replaced with new theories. These but he had probably also seen a The Greeks called these wandering
in turn are only theories, and may copy of Alhazen’s Optics. stars “planets.” The Chinese
yet be disproved, although in many spotted Halley’s comet in 240 BCE
cases this is unlikely given the The first scientists and, in 1054, a supernova that is
evidence in their support. The first philosophers with a now known as the Crab Nebula. ❯❯
scientific outlook were active in
Progression of ideas the ancient Greek world during the If you would be a real seeker
Science rarely proceeds in simple, 6th and 5th centuries BCE. Thales after truth, it is necessary
logical steps. Discoveries may be of Miletus predicted an eclipse of that at least once in your
made simultaneously by scientists the Sun in 585 BCE; Pythagoras set life you doubt, as far as
working independently, but almost up a mathematical school in what possible, all things.
every advance depends in some is now southern Italy 50 years later, René Descartes
measure on previous work and and Xenophanes, after finding
theories. One reason for building seashells on a mountain, reasoned
the vast apparatus known as the that the whole Earth must at one
Large Hadron Collider, or LHC, was time have been covered by sea.
to search for the Higgs particle,
whose existence was predicted In Sicily in the 4th century BCE,
40 years earlier, in 1964. That Empedocles asserted that earth,
prediction rested on decades of air, fire, and water are the “fourfold
theoretical work on the structure of roots of everything.” He also took
the atom, going back to Rutherford his followers up to the volcanic
and the work of Danish physicist crater of Mt. Etna and jumped in,

14 INTRODUCTION

House of Wisdom the center of the universe, Isaac Newton’s Philosophiæ
In the late 8th century CE, the overturning the Earth-centered Naturalis Principia Mathematica,
Abbasid caliphate set up the House model figured out by Ptolemy of commonly known as the Principia.
of Wisdom, a magnificent library, Alexandria a millennium earlier. His laws of motion and principle of
in its new capital, Baghdad. This universal gravity form the basis for
inspired rapid advances in Islamic In 1600, English physician classical physics.
science and technology. Many William Gilbert published De
ingenious mechanical devices were Magnete in which he explained Elements, atoms, evolution
invented, along with the astrolabe, that compass needles point north In the 18th century, French chemist
a navigational device that used the because Earth itself is a magnet. Antoine Lavoisier discovered the
positions of the stars. Alchemy He even argued that Earth’s core role of oxygen in combustion,
flourished, and techniques such as is made of iron. In 1623, another discrediting the old theory of
distillation appeared. Scholars at English physician, William Harvey, phlogiston. Soon a host of new
the library collected all the most described for the first time how the gases and their properties were
important books from Greece and heart acts as a pump and drives being investigated. Thinking about
from India, and translated them blood around the body, thereby the gases in the atmosphere led
into Arabic, which is how the West quashing forever earlier theories British meteorologist John Dalton to
later rediscovered the works of that dated back 1,400 years to the
the ancients, and learned of the Greco-Roman physician Galen. I seem to have been only
“Arabic” numerals, including zero, In the 1660s, Anglo-Irish chemist like a boy playing on the
that were imported from India. Robert Boyle produced a string seashore, and diverting myself
of books, including The Sceptical in now and then finding a
Birth of modern science Chymist, in which he defined a smoother pebble…whilst the
As the monopoly of the Church over chemical element. This marked the great ocean of truth lay all
scientific truth began to weaken in birth of chemistry as a science, as undiscovered before me.
the Western world, the year 1543 distinct from the mystical alchemy
saw the publication of two ground- from which it arose. Isaac Newton
breaking books. Belgian anatomist
Andreas Vesalius produced De Robert Hooke, who worked for a
Humani Corporis Fabrica, which time as Boyle’s assistant, produced
described his dissections of human the first scientific best seller,
corpses with exquisite illustrations. Micrographia, in 1665. His superb
In the same year, Polish physician fold-out illustrations of subjects
Nicolaus Copernicus published De such as a flea and the eye of a fly
Revolutionibus Orbium Coelestium, opened up a microscopic world no
which stated firmly that the Sun is one had seen before. Then in 1687
came what many view as the most
important science book of all time,

INTRODUCTION 15

suggest that each element Uncertainty and infinity expanding, and started with a
consisted of unique atoms, and At the turn of the 20th century, Big Bang. The idea of black holes
propose the idea of atomic weights. a young German named Albert began to take root. Dark matter and
Then German chemist August Einstein proposed his theory of dark energy, whatever they were,
Kekulé developed the basis of relativity, shaking classical physics seemed to fill the universe, and
molecular structure, while Russian and ending the idea of an absolute astronomers began to discover
inventor Dmitri Mendeleev laid out time and space. New models of new worlds—planets in orbit
the first generally accepted periodic the atom were proposed; light was around distant stars, some of
table of the elements. shown to act as both a particle which may even harbor life. British
and a wave; and another German, mathematician Alan Turing
The invention of the electric Werner Heisenberg, demonstrated thought of the universal computing
battery by Alessandro Volta in Italy that the universe was uncertain. machine, and within 50 years
in 1799 opened up new fields of we had personal computers, the
science, into which marched What has been most impressive worldwide web, and smartphones.
Danish physicist Hans Christian about the last century, however,
Ørsted and British contemporary is how technical advances have Secrets of life
Michael Faraday, discovering new enabled science to advance faster In biology, chromosomes were
elements and electromagnetism, than ever before, leap-frogging shown to be the basis of inheritance
which led to the invention of the ideas with increasing precision. and the chemical structure of DNA
electric motor. Meanwhile, the ideas Ever more powerful particle was decoded. Just 40 years later
of classical physics were applied to colliders revealed new fundamental this led to the human genome
the atmosphere, the stars, the units of matter. Stronger telescopes project, which seemed a daunting
speed of light, and the nature of showed that the universe is task in prospect, and yet, aided by
heat, which developed into the computing, got faster and faster as
science of thermodynamics. Reality is merely an illusion, it progressed. DNA sequencing is
albeit a very persistent one. now an almost routine laboratory
Geologists studying rock strata operation, gene therapy has moved
began to reconstruct Earth’s past. Albert Einstein from a hope into reality, and the
Paleontology became fashionable first mammal has been cloned.
as the remains of extinct creatures
began to turn up. Mary Anning, an As today’s scientists build on
untutored British girl, became a these and other achievements,
world-famous assembler of fossil the relentless search for the truth
remains. With the dinosaurs came continues. It seems likely that there
ideas of evolution, most famously will always be more questions than
from British naturalist Charles answers, but future discoveries will
Darwin, and new theories on the surely continue to amaze. ■
origins and ecology of life.

THE BEG

OF SCIE

600 BCE–14O0 CE

INNING

NCE

18 INTRODUCTION

Thales of Miletus Xenophanes finds Aristotle writes a string Aristarchus of Samos
predicts the eclipse of seashells on mountains, of books on subjects suggests that the Sun,
and concludes that the including physics,
the Sun that brings whole Earth was once rather than Earth,
the Battle of Halys covered with water. biology, and zoology. is the center of
the universe.
to an end.

585 BCE C.500 BCE C.325 BCE C.250 BCE

C.530 BCE C.450 BCE C.300 BCE C.240 BCE

Pythagoras founds a Empedocles suggests Theophrastus writes Archimedes discovers
mathematical school at that everything on Enquiry into plants that a king’s crown
Earth is made from and The causes of is not pure gold by
Croton in what is now measuring the
southern Italy. combinations of earth, plants, founding upthrust of
air, fire, and water. the discipline displaced water.

of botany.

T he scientific study of the scientific is probably Thales of explored the properties of fluids.
world has its roots in Miletus, of whom Plato said that A new center of learning developed
Mesopotamia. Following he spent so much time dreaming at Alexandria, founded at the
the invention of agriculture and and looking at the stars that he mouth of the Nile by Alexander the
writing, people had the time to once fell into a well. Possibly using Great in 331 BCE. Here Eratosthenes
devote to study and the means data from earlier Babylonians, measured the size of Earth,
to pass the results of those studies in 585 BCE, Thales predicted a Ctesibius made accurate clocks,
on to the next generation. Early solar eclipse, demonstrating the and Hero invented the steam
science was inspired by the wonder power of a scientific approach. engine. Meanwhile, the librarians
of the night sky. From the fourth in Alexandria collected the best
millennium BCE, Sumerian priests Ancient Greece was not a books they could find to build the
studied the stars, recording their single country, but rather a loose best library in the world, which was
results on clay tablets. They did collection of city states. Miletus burned down when Romans and
not leave records of their methods, (now in Turkey) was the birthplace Christians took over the city.
but a tablet dating from 1800 BCE of several noted philosophers. Many
shows knowledge of the properties other early Greek philosophers Science in Asia
of right-angled triangles. studied in Athens. Here, Aristotle Science flourished independently
was an astute observer, but he in China. The Chinese invented
Ancient Greece did not conduct experiments; gunpowder—and with it fireworks,
The ancient Greeks did not see he believed that, if he could bring rockets, and guns—and made
science as a separate subject together enough intelligent men, bellows for working metal. They
from philosophy, but the first the truth would emerge. The invented the first seismograph
figure whose work is recognizably engineer Archimedes, who lived at and the first compass. In 1054 CE,
Syracuse on the island of Sicily,

THE BEGINNING OF SCIENCE 19

Eratosthenes, a friend of Hipparchus discovers Claudius Ptolemy’s Persian astronomer,
Archimedes, calculates the precession of Almagest becomes the Abd al-Rahman
the circumference of Earth’s orbit and authoritative text on
Earth from the shadows al-Sufi updates the
of the Sun at midday on compiles the Western astronomy in the Almagest, and gives
world’s first star West, even though it
midsummer day. catalogue. contains many errors. many stars the
Arabic names

used today.

C.240 BCE C.130 BCE C.150 CE 964

C.230 BCE C.120 CE 628 1021

Ctesibius builds In China, Zhang Heng Indian mathematician Alhazen, one of the
clepsydras—water discusses the nature of Brahmagupta outlines first experimental
clocks—that remain for eclipses, and compiles scientists, conducts
centuries the most the first rules to use original research on
accurate timepieces a catalogue of the number zero. vision and optics.
2,500 stars.
in the world.

Chinese astronomers observed a of a martyr,” Caliph Harun al-Rashid Alhazen, born in Basra and
supernova, which was identified founded the House of Wisdom in educated in Baghdad, was one of
as the Crab Nebula in 1731. his new capital, intending it to be the first experimental scientists,
a library and center for research. and his book on optics has been
Some of the most advanced Scholars collected books from the likened in importance to the work
technology in the first millennium old Greek city states and India and of Isaac Newton. Arab alchemists
CE, including the spinning wheel, translated them into Arabic. This devised distillation and other new
was developed in India, and is how many of the ancient texts techniques, and coined words such
Chinese missions were sent to would eventually reach the West, as alkali, aldehyde, and alcohol.
study Indian farming techniques. where they were largely unknown Physician al-Razi introduced soap,
Indian mathematicians developed in the Middle Ages. By the middle distinguished for the first time
what we now call the “Arabic” of the 9th century, the library in between smallpox and measles,
number system, including negative Baghdad had grown to become and wrote in one of his many books
numbers and zero, and gave a fine successor to the library “The doctor’s aim is to do good,
definitions of the trigonometric at Alexandria. even to our enemies.” Al-Khwarizmi
functions sine and cosine. and other mathematicians invented
Among those who were inspired algebra and algorithms; and
The Golden Age of Islam by the House of Wisdom were engineer al-Jazari invented the
In the middle of the 8th century, several astronomers, notably al-Sufi, crank-connecting rod system,
the Islamic Abbasid Caliphate who built on the work of Hipparchus which is still used in bicycles and
moved the capital of its empire from and Ptolemy. Astronomy was of cars. It would take several centuries
Damascus to Baghdad. Guided by practical use to Arab nomads for for European scientists to catch up
the Quranic slogan “The ink of a navigation, since they steered their with these developments. ■
scholar is more holy than the blood camels across the desert at night.

20

ECLIPSES OF
THE SUN CAN
BE PREDICTED

THALES OF MILETUS (624–546 BCE)

IN CONTEXT B orn in a Greek colony in solar eclipse, now dated to May 28,
Asia Minor, Thales of 585 BCE, which famously brought a
BRANCH Miletus is often viewed as battle between the warring Lydians
Astronomy the founder of Western philosophy, and Medes to a halt.
but he was also a key figure in the
BEFORE early development of science. He Contested history
c.2000 BCE European was recognized in his lifetime for Thales’s achievement was not to be
monuments such as his thinking on mathematics, repeated for several centuries, and
Stonehenge may have been physics, and astronomy. historians of science have long
used to calculate eclipses. argued about how, and even if,
Perhaps Thales’s most famous he achieved it. Some argue that
c.1800 BCE In ancient Babylon, achievement is also his most Herodotus’s account is inaccurate
astronomers produce the first controversial. According to the and vague, but Thales’s feat seems
recorded mathematical Greek historian Herodotus, writing to have been widely known and
description of the movement more than a century after the event, was taken as fact by later writers,
of heavenly bodies. Thales is said to have predicted a who knew to treat Herodotus’s
word with caution. Assuming it
2nd millennium BCE …day became night, and this is true, it is likely that Thales had
Babylonian astronomers change of the day Thales the discovered an 18-year cycle in
develop methods for the movements of the Sun and
predicting eclipses, but Milesian had foretold… Moon, known as the Saros cycle,
these are based on Herodotus which was used by later Greek
observations of the Moon, astronomers to predict eclipses.
not mathematical cycles.
Whatever method Thales used,
AFTER his prediction had a dramatic effect
c.140 BCE Greek astronomer on the battle at the river Halys, in
Hipparchus develops a modern-day Turkey. The eclipse
system to predict eclipses ended not only the battle, but also
using the Saros cycle of a 15-year war between the Medes
movements of the Sun and the Lydians. ■
and Moon.
See also: Zhang Heng 26–27 ■ Nicolaus Copernicus 34–39 ■
Johannes Kepler 40–41 ■ Jeremiah Horrocks 52

THE BEGINNING OF SCIENCE 21

NOW HEAR THE
FOURFOLD ROOTS
OF EVERYTHING

EMPEDOCLES (490–430 BCE)

IN CONTEXT T he nature of matter Empedocles saw the four roots
concerned many ancient of matter as two pairs of opposites:
BRANCH Greek thinkers. Having fire/water and air/earth, which
Chemistry seen liquid water, solid ice, and combine to produce everything we see.
gaseous mist, Thales of Miletus
BEFORE believed that everything must be Fire
c.585 BCE Thales suggests the made of water. Aristotle suggested
whole world is made of water. that “nourishment of all things is Hot Dry
moist and even the hot is created
c.535 BCE Anaximenes thinks from the wet and lives by it.” Air Earth
that everything is made from Writing two generations after
air, from which water and then Thales, Anaximenes suggested Wet Cold
stones are made. that the world is made of air,
reasoning that when air condenses Water
AFTER it produces mist, and then rain,
c.400 BCE The Greek thinker and eventually stones. centrifugal force, began to pull
Democritus proposes that the them apart. For Empedocles, love
world is ultimately made of tiny Born at Agrigentum on the and strife are the two forces that
indivisible particles—atoms. island of Sicily, the physician and shape the universe. In this world,
poet Empedocles devised a more strife tends to predominate, which
1661 In his work Sceptical complex theory: that everything is is why life is so difficult.
Chymist, Robert Boyle provides made of four roots—he did not use
a definition of elements. the word elements—namely earth, This relatively simple theory
air, fire, and water. Combining dominated European thought—
1808 John Dalton’s atomic these roots would produce qualities which referred to the “four
theory states that each element such as heat and wetness to make humors”—with little refinement
has atoms of different masses. earth, stone, and all plants and until the development of modern
animals. Originally, the four roots chemistry in the 17th century. ■
1869 Dmitri Mendeleev formed a perfect sphere, held
proposes a periodic table, together by love, the centripetal
arranging the elements in force. But gradually strife, the
groups according to their
shared properties. See also: Robert Boyle 46–49 ■ John Dalton 112–13 ■ Dmitri Mendeleev 174–79

22

MEASURING THE
CIRCUMFERENCE
OF EARTH

ERATOSTHENES (276–194 BCE)

IN CONTEXT T he Greek astronomer 7.2° south of the zenith—which is
and mathematician 1/50th of the circumference of a
BRANCH Eratosthenes is best circle. Therefore, he reasoned, the
Geography remembered as the first person to separation of the two cities along
measure the size of Earth, but he a north–south meridian must be
BEFORE is also regarded as the founder of 1/50th of Earth’s circumference.
6th century BCE Greek geography—not only coining the This allowed him to figure out the
mathematician Pythagoras word, but also establishing many size of our planet at 230,000 stadia,
suggests Earth may be of the basic principles used to or 24,662 miles (39,690 km)—an
spherical, not flat. measure locations on our planet. error of less than 2 percent. ■
Born at Cyrene (in modern-day
3rd century BCE Aristarchus Libya), Eratosthenes traveled Sunlight reached Swenet at right
of Samos is the first to place widely in the Greek world, studying angles, but cast a shadow at Alexandria.
the Sun at the center of the in Athens and Alexandria, and The angle of the shadow cast by the
known universe and uses eventually becoming the librarian gnomon allowed Eratosthenes to
a trigonometric method to of Alexandria’s Great Library. calculate Earth’s circumference.
estimate the relative sizes of
the Sun and the Moon and It was in Alexandria that 7.2˚
their distances from Earth. Eratosthenes heard a report that
at the town of Swenet, south of Alexandria Gnomon
Late 3rd century BCE Alexandria, the Sun passed directly 7.2˚
Eratosthenes introduces the overhead on the summer solstice
concepts of parallels and (the longest day of the year, when Swenet
meridians to his maps the Sun rises highest in the sky).
(equivalent to modern Assuming the Sun was so distant Earth
longitude and latitude). that its rays were almost parallel to
each other when they hit Earth, he Sunrays
AFTER used a vertical rod, or “gnomon,”
18th century The true to project the Sun’s shadow at
circumference and shape the same moment in Alexandria.
of Earth is found through Here, he determined, the Sun was
enormous efforts by French
and Spanish scientists. See also: Nicolaus Copernicus 34–39 ■ Johannes Kepler 40–41

THE BEGINNING OF SCIENCE 23

THE HUMAN IS
RELATED TO THE
LOWER BEINGS

AL-TUSI (1201–1274)

IN CONTEXT A Persian scholar born in The organisms that can
Baghdad in 1201, during gain the new features faster
BRANCH the Golden Age of Islam, are more variable. As a result,
Biology Nazir al-Din al-Tusi was a poet,
philosopher, mathematician, and they gain advantages
BEFORE astronomer, and one of the first to over other creatures.
c.550 BCE Anaximander of propose a system of evolution. He
Miletus proposes that animal suggested that the universe had al-Tusi
life began in the water, and once comprised identical elements
evolved from there. that had gradually drifted apart, Al-Tusi believed that organisms
with some becoming minerals and changed over time, seeing in that
c.340 BCE Plato’s theory of others, changing more quickly, change a progression toward
forms argues that species developing into plants and animals. perfection. He thought of humans
are unchangeable. as being on a “middle step of the
In Akhlaq-i-Nasri, al-Tusi’s work evolutionary stairway,” potentially
c.300 BCE Epicurus says that on ethics, he set out a hierarchy of able by means of their will to reach
many other species have been life forms, in which animals were a higher developmental level. He
created in the past, but only higher than plants and humans was the first to suggest that not
the most successful survive were higher than other animals. only do organisms change over
to have offspring. He regarded the conscious will time, but that the whole range of
of animals as a step toward the life has evolved from a time when
AFTER consciousness of humans. Animals there was no life at all. ■
1377 Ibn Khaldun writes in are able to move consciously to
Muqaddimah that humans search for food, and can learn
developed from monkeys. new things. In this ability to learn,
al-Tusi saw an ability to reason:
1809 Jean-Baptiste Lamarck “The trained horse or hunting
proposes a theory of evolution falcon is at a higher point of
of species. development in the animal world,”
he said, adding, “The first steps of
1858 Alfred Russel Wallace human perfection begin from here.”
and Charles Darwin suggest
a theory of evolution by means See also: Carl Linnaeus 74–75 ■ Jean-Baptiste Lamarck 118 ■
of natural selection. Charles Darwin 142–49 ■ Barbara McClintock 271

24

A FLOATING OBJECT
DISPLACES ITS OWN
VOLUME IN LIQUID

ARCHIMEDES (287–212 BCE)

IN CONTEXT T he Roman author Vitruvius, had substituted silver for some of
writing in the 1st century the gold, melting the silver with the
BRANCH BCE, recounts the possibly remaining gold so that the color
Physics apocryphal story of an incident that looked the same as pure gold.
happened two centuries earlier. The king asked his chief scientist,
BEFORE Hieron II, the King of Sicily, had Archimedes, to investigate.
3rd millennium BCE ordered a new gold crown. When
Metalworkers discover that the crown was delivered, Hieron Archimedes puzzled over the
melting metals and mixing suspected that the crown maker problem. The new crown was
them together produces an precious, and must not be damaged
alloy that is stronger than
either of the original metals. Silver is less dense A crown made
than gold, so a lump partly of silver will have
600 BCE In ancient Greece, greater volume and displace
coins are made from an alloy of of silver will have a more water than a lump
gold and silver called electrum. greater volume than of pure gold of the same
a lump of gold of the
AFTER weight as the crown.
1687 In his Principia same weight.
Mathematica, Isaac Newton
outlines his theory of gravity, The difference in The displaced water
explaining how there is a force upthrust between the causes an upthrust.
that pulls everything toward two is small, but it can The partly silver crown
the center of Earth—and be detected if you hang experiences a greater
vice versa. them on a balance in water. upthrust than the gold.

1738 Swiss mathematician Eureka!
Daniel Bernoulli develops
his kinetic theory of fluids,
explaining how fluids exert
pressure on objects by the
random movement of
molecules in the fluid.

THE BEGINNING OF SCIENCE 25

See also: Nicolaus Copernicus 34–39 ■ Isaac Newton 62–69

in any way. He went to the public realized that any object immersed A solid heavier than a fluid
baths in Syracuse to ponder the in a liquid experiences an upthrust will, if placed in it, descend to
problem. The bath was full to the (upward force) equal to the weight the bottom of the fluid, and the
brim, and when he climbed in, he of the liquid it has displaced.
noticed two things: the water level solid will, when weighed in
rose, making some water slop over Archimedes probably solved the the fluid, be lighter than its
the side, and he felt weightless. He puzzle by hanging the crown and true weight by the weight of
shouted “Eureka!” (I have found the an equal weight of pure gold on
answer!) and ran home stark naked. opposite ends of a stick, which he the fluid displaced.
then suspended by its center so Archimedes
Measuring volume that the two weights balanced.
Archimedes had realized that Then he lowered the whole thing it has displaced one ton of water,
if he lowered the crown into a into a bath of water. If the crown but then will sink no further. Its
bucket filled to the brim with water, was pure gold, it and the lump of deep, hollow hull has a greater
it would displace some water— gold would experience an equal volume and displaces more water
exactly the same amount as its own upthrust, and the stick would stay than a lump of steel of the same
volume—and he could measure horizontal. If the crown contained weight, and is therefore buoyed up
how much water spilled out. This some silver, however, the volume by a greater upthrust.
would tell him the volume of the of the crown would be greater than
crown. Silver is less dense than the volume of the lump of gold—the Vitruvius tells us that Hieron’s
gold, so a silver crown of the same crown would displace more water, crown was indeed found to contain
weight would be bigger than a gold and the stick would tilt sharply. some silver, and that the crown
crown, and would displace more maker was duly punished. ■
water. Therefore, an adulterated Archimedes’ idea became
crown would displace more water known as Archimedes’ principle,
than a pure gold crown—and more which states that the upthrust on
than a lump of gold of the same an object in a fluid is equal to the
weight. In practice, the effect would weight of the fluid the object
have been small and difficult to displaces. This principle explains
measure. But Archimedes had also how objects made of dense material
can still float on water. A steel ship
that weighs one ton will sink until

Archimedes Archimedes was possibly the Archimedes also calculated an
greatest mathematician in approximation for pi (the ratio
the ancient world. Born around of a circle’s circumference to
287 BCE, he was killed by a soldier its diameter), and wrote down
when his home town Syracuse the laws of levers and pulleys.
was taken by the Romans in The achievement Archimedes
212 BCE. He had devised several was most proud of was a
fearsome weapons to keep at bay mathematical proof that the
the Roman warships that attacked smallest cylinder that any given
Syracuse—a catapult, a crane to sphere can fit into has exactly
lift the bows of a ship out of the 1.5 times the sphere’s volume. A
water, and a death array of mirrors sphere and a cylinder are carved
to focus the Sun’s rays and set into Archimedes’ tombstone.
fire to a ship. He probably
invented the Archimedes screw, Key work
still used today for irrigation,
during a stay in Egypt. c.250 BCE On Floating Bodies

26

THE SUN IS LIKE
FIRE, THE MOON
IS LIKE WATER

ZHANG HENG (78–139 CE)

IN CONTEXT During the day I n about 140 BCE, the Greek
Earth is bright, with astronomer Hipparchus,
BRANCH probably the finest astronomer
Physics shadows, because of the ancient world, compiled a
of sunlight. catalogue of some 850 stars. He
BEFORE also explained how to predict the
140 BCE Hipparchus figures The Moon is sometimes movements of the Sun and Moon
out how to predict eclipses. bright, with shadows. and the dates of eclipses. In his
work Almagest of about 150 CE,
150 CE Ptolemy improves The Moon Ptolemy of Alexandria listed
on Hipparchus’s work, and must be bright 1,000 stars and 48 constellations.
produces practical tables for because of sunlight. Most of this work was effectively
calculating the future positions an updated version of what
of the celestial bodies. Therefore the Sun Hipparchus had written, but in a
is like fire, the Moon more practical form. In the West,
AFTER the Almagest became the standard
11th century Shen Kuo like water. astronomy text throughout the
writes the Dream Pool Essays, Middle Ages. Its tables included
in which he uses the waxing all the information needed to
and waning of the Moon to calculate the future positions of the
demonstrate that all heavenly Sun and Moon, the planets and
bodies (though not Earth) the major stars, and also eclipses
are spherical. of the Sun and Moon.

1543 Nicolaus Copernicus In 120 CE, the Chinese polymath
publishes On the Revolutions Zhang Heng produced a work
of the Celestial Spheres, entitled Ling Xian, or The Spiritual
in which he describes a Constitution of the Universe. In it,
heliocentric system. he wrote that “the sky is like a
hen’s egg, and is as round as a
1609 Johannes Kepler crossbow pellet, and Earth is like
explains the movements of the yolk of the egg, lying alone at
the planets as free-floating the center. The sky is large and the
bodies describing ellipses. Earth small.” This was, following
Hipparchus and Ptolemy, a universe

THE BEGINNING OF SCIENCE 27

See also: Nicolaus Copernicus 34–39 ■ Johannes Kepler 40–41 ■
Isaac Newton 62–69

The Moon and the planets Sun, and the Moon’s darkness is Zhang Heng
are Yin; they have shape due to the light of the Sun being
obstructed. The side that faces the Zhang Heng was born in 78 CE
but no light. Sun is fully lit, and the side that is in the town of Xi’e, in what is
Jing Fang away from it is dark.” Zhang also now Henan Province, in Han
described a lunar eclipse, where Dynasty China. At 17, he left
with Earth at its center. Zhang the Sun’s light cannot reach the home to study literature and
catalogued 2,500 “brightly shining” Moon because Earth is in the way. train to be a writer. By his late
stars and 124 constellations, and He recognized that the planets 20s, Zhang had become a
added that “of the very small stars were also “like water,” reflecting skilled mathematician and
there are 11,520.” light, and so were also subject to was called to the court of
eclipses: “When [a similar effect] Emperor An-ti, who, in 115 CE,
Eclipses of the Moon happens with a planet, we call it an made him Chief Astrologer.
and planets occultation; when the Moon passes
Zhang was fascinated by eclipses. across the Sun’s path then there is Zhang lived at a time of
He wrote, “The Sun is like fire and a solar eclipse.” rapid advances in science. In
the Moon like water. The fire gives addition to his astronomical
out light and the water reflects it. In the 11th century, another work, he devised a water-
Thus the Moon’s brightness is Chinese astronomer, Shen Kuo, powered armillary sphere (a
produced from the radiance of the expanded on Zhang’s work in one model of the celestial objects)
significant respect. He showed that and invented the world’s first
observations of the waxing and seismometer, which was
waning of the Moon proved that the ridiculed until, in 138 CE, it
celestial bodies were spherical. ■ successfully recorded an
earthquake 250 miles (400 km)
The crescent outline of Venus is away. He also invented the
about to be occulted by the Moon. first odometer to measure
Zhang’s observations led him to distances traveled in vehicles,
conclude that, like the Moon, the and a nonmagnetic, south-
planets did not produce their own light. pointing compass in the form
of a chariot. Zhang was a
distinguished poet, whose
works give us vivid insights
into the cultural life of his day.

Key works

c.120 CE The Spiritual
Constitution of the Universe
c.120 CE The Map of
the Ling Xian

28

LIGHT TRAVELS
IN STRAIGHT LINES
INTO OUR EYES

ALHAZEN (c.965–1040)

IN CONTEXT The light of the Sun The light bounces off
bounces off objects. in straight lines.
BRANCH
Physics Light travels in To see, we need to do nothing
straight lines into but open our eyes.
BEFORE
350 BCE Aristotle argues that our eyes.
vision derives from physical
forms entering the eye from T he Arab astronomer and methodically testing them with
an object. mathematician Alhazen, experiments. As he observed:
who lived in Baghdad, “The seeker after truth is not one
300 BCE Euclid argues that the in present-day Iraq, during the who studies the writings of the
eye sends out beams that are Golden Age of Islamic civilization, ancients and…puts his trust in
bounced back to the eye. was arguably the world’s first them, but rather the one who
experimental scientist. While suspects his faith in them and
980s Ibn Sahl investigates earlier Greek and Persian thinkers questions what he gathers from
refraction of light and deduces had explained the natural world in them, the one who submits to
the laws of refraction. various ways, they had arrived at argument and demonstration.”
their conclusions through abstract
AFTER reasoning, not through physical Understanding vision
1240 English bishop Robert experiments. Alhazen, working in a Alhazen is remembered today as
Grosseteste uses geometry in thriving Islamic culture of curiosity a founder of the science of optics.
his experiments with optics and inquiry, was the first to use His most important works were
and accurately describes the what we now call the scientific studies of the structure of the eye
nature of color. method: setting up hypotheses and and the process of vision. The

1604 Johannes Kepler’s theory
of the retinal image is based
directly on Alhazen’s work.

1620s Alhazen’s ideas
influence Francis Bacon, who
advocates a scientific method
based on experiment.

THE BEGINNING OF SCIENCE 29

See also: Johannes Kepler 40–41 ■ Francis Bacon 45 ■ Christiaan Huygens 50–51 ■ Isaac Newton 62–69

Object Image is upside down and is focused by a lens onto a
and back to front sensitive surface (the retina) at
the back of the eye. However, even
Pinhole though he recognized the eye as a
lens, he did not explain how the
eye or the brain forms an image.

Light rays Alhazen provided the first scientific Experiments with light
travel from description of a camera obscura, an Alhazen’s monumental, seven-
the object optical device that projects an volume Book of Optics set out his
upside-down image on a screen. theory of light and his theory of
vision. It remained the main
Greek scholars Euclid and, later, He noted that, “from each point of authority on the subject until
Ptolemy believed that vision every colored body, illuminated Newton’s Principia was published
derived from “rays” that beamed by any light, issue light and color 650 years later. The book explores
out of the eye and bounced back along every straight line that the interaction of light with lenses,
from whatever a person was looking can be drawn from that point.” and describes the phenomenon of
at. Alhazen showed, through In order to see things, we have only refraction (change in the direction)
the observation of shadows and to open our eyes to let in the light. of light—700 years before Dutch
reflection, that light bounces off There is no need for the eye to send scientist Willebrord van Roijen
objects and travels in straight lines out rays, even if it could. Snell’s law of refraction. It also
into our eyes. Vision was a passive, examines the refraction of light
rather than an active, phenomenon, Alhazen also found, through his by the atmosphere, and describes
at least until it reached the retina. experiments with bulls’ eyes, that shadows, rainbows, and eclipses.
light enters a small hole (the pupil) Optics greatly influenced later
Western scientists, including
Francis Bacon, one of the scientists
responsible for reviving Alhazen’s
scientific method during the
Renaissance in Europe. ■

The duty of the man Alhazen traveled south of the city, and
who investigates the saw the sheer size of the river—
writings of scientists, if Abu Ali al-Hassan ibn al- which is almost 1 mile (1.6 km)
learning the truth is his Haytham (known in the West as wide at Aswan—he realized the
goal, is to make himself an Alhazen) was born in Basra, in task was impossible with the
enemy of all that he reads. present-day Iraq, and educated technology then available. To
in Baghdad. As a young man he avoid the caliph’s retribution he
Alhazen was given a government job in feigned insanity and remained
Basra, but soon became bored. under house arrest for 12 years.
One story has it that, on hearing In that time he did his most
about the problems resulting important work.
from the annual flooding of
the Nile in Egypt, he wrote to Key works
Caliph al-Hakim offering to build
a dam to regulate the deluge, 1011–21 Book of Optics
and was received with honor c.1030 A Discourse on Light
in Cairo. However, when he c.1030 On the Light of the Moon

SCIENTI

REVOLU

1400–1700

FIC

TION

32 INTRODUCTION

Nicolaus Copernicus Johannes Kepler suggests Francis Bacon publishes Evangelista Torricelli
publishes De that Mars has an Novum Organum invents the barometer.
elliptical orbit.
Revolutionibus Orbium Scientarum and The
Coelestium, outlining New Atlantis, outlining
the scientific method.
a heliocentric
universe.

1543 1609 1620S 1643

1600 1610 1639 1660S

Astronomer William Gilbert Galileo observes the Jeremiah Horrocks Robert Boyle publishes
publishes De Magnete, a moons of Jupiter and
treatise on magnetism, experiments with balls observes the transit New Experiments
and suggests that
Earth is a magnet. rolling down slopes. of Venus. Physico-Mechanical:

Touching the Spring of

the Air, and its Effects,

investigating air pressure.

T he Islamic Golden Age Nicolaus Copernicus completed his objects and devising the pendulum
was a great flowering of heretical model of the universe that as an effective timekeeper, which
the sciences and arts had the Sun at its center. Aware of Dutchman Christiaan Huygens
that began in the capital of the the heresy, he was careful to state used to build the first pendulum
Abbasid Caliphate, Baghdad, in that it was only a mathematical clock in 1657. English philosopher
the mid-8th century and lasted model, and he waited until he Francis Bacon wrote two books
for about 500 years. It laid the was on the point of death before laying out his ideas for a scientific
foundations for experimentation publishing, but the Copernican method, and the theoretical
and the modern scientific method. model quickly won many advocates. groundwork for modern science,
In the same period in Europe, German astrologer Johannes Kepler based on experiment, observation,
however, several hundred years refined Copernicus’s theory using and measurement, was developed.
were to pass before scientific observations by his Danish mentor
thought was to overcome the Tycho Brahe, and calculated that the New discoveries followed thick
restrictions of religious dogma. orbits of Mars and, by inference, and fast. Robert Boyle used an air
the other planets were ellipses. pump to investigate the properties
Dangerous thinking Improved telescopes allowed Italian of air, while Huygens and English
For centuries, the Catholic Church’s polymath Galileo Galilei to identify physicist Isaac Newton came up
view of the universe was based on four moons of Jupiter in 1610. The with opposing theories of how light
Aristotle’s idea that Earth was at new cosmology’s explanatory travels, establishing the science
the orbital center of all celestial power was becoming undeniable. of optics. Danish astronomer Ole
bodies. Then, in about 1532, after Rømer noted discrepancies in
years of struggling with its complex Galileo also demonstrated the the timetable of eclipses of the
mathematics, Polish physician power of scientific experiment, moons of Jupiter, and used these
investigating the physics of falling to calculate an approximate value

SCIENTIFIC REVOLUTION 33

In Micrographia, Jan Swammerdam Ole Rømer uses the John Ray publishes
Robert Hooke describes how moons of Jupiter to Historia Plantarum, an
show that light has encyclopedia of the
introduces the world insects develop in
to the anatomy of stages in Historia a finite speed. plant kingdom.
fleas, bees, and cork. Insectorum Generalis.

1665 1669 1676 1686 1687
1669 1670S 1678

Nicolas Steno writes Antonie van Christiaan Huygens first Isaac Newton outlines
about solids (fossils and Leeuwenhoek observes announces his wave his laws of motion
theory of light, which
crystals) contained single-celled will later contrast with in Philosophiae
within solids. organisms, sperm, and Isaac Newton’s idea of Naturalis Principia
light as corpuscular.
even bacteria with Mathematica.
simple microscopes.

for the speed of light. Rømer’s Antonie van Leeuwenhoek, enormous encyclopedia of plants,
compatriot, Bishop Nicolas Steno, perhaps inspired by Hooke’s which marked the first serious
was sceptical of much ancient drawings, made hundreds of his attempt at systematic classification.
wisdom, and developed his own own microscopes and found tiny
ideas in both anatomy and geology. life forms in places where no one Mathematical analysis
He laid down the principles of had thought of looking before, such Heralding the Enlightenment, these
stratigraphy (the study of rock as water. Leeuwenhoek had discoveries laid the groundwork for
layers), establishing a new discovered single-celled life forms the modern scientific disciplines of
scientific basis for geology. such as protists and bacteria, astronomy, chemistry, geology,
which he called “animalcules.” physics, and biology. The century’s
Microworlds When he reported his findings to crowning achievement came with
Throughout the 17th century, the British Royal Society, they sent Newton’s treatise Philosophiæ
developments in technology three priests to certify that he had Naturalis Principia Mathematica,
drove scientific discovery at the really seen such things. Dutch which laid out his laws of motion
smallest scale. In the early 1600s, microscopist Jan Swammerdam and gravity. Newtonian physics
Dutch eyeglasses-makers showed that egg, larva, pupa, was to remain the best description
developed the first microscopes, and adult are all stages in the of the physical world for more than
and, later that century, Robert development of an insect, and not two centuries, and together with
Hooke built his own and made separate animals created by God. the analytical techniques of
beautiful drawings of his findings, Old ideas dating back to Aristotle calculus developed independently
revealing the intricate structure of were swept away by these new by Newton and Gottfried Wilhelm
tiny bugs such as fleas for the first discoveries. Meanwhile, English Leibniz, it would provide a powerful
time. Dutch fabric-store owner biologist John Ray compiled an tool for future scientific study. ■

AT THE CENTER

SUNOFEVERYTHING IS THE

NICOLAUS COPERNICUS (1473–1543)



36 NICOLAUS COPERNICUS

IN CONTEXT T hroughout its early history, If the Lord Almighty
Western thought was had consulted me before
BRANCH shaped by an idea of embarking on creation thus,
Astronomy the universe that placed Earth I should have recommended
at the center of everything. This
BEFORE “geocentric model” seemed at something simpler.
3rd century BCE In a work first to be rooted in everyday Alfonso X
called The Sand Reckoner, observations and common sense—
Archimedes reports the ideas we do not feel any motion of the King of Castile
of Aristarchus of Samos, who ground on which we stand, and
proposed that the universe superficially there seems to be no the Sun. Mars, Jupiter, and Saturn,
was much larger than observational evidence that our meanwhile, took 780 days, 12 years,
commonly believed, and that planet is in motion either. Surely and 30 years respectively to circle
the Sun was at its center. the simplest explanation was against the background stars, their
that the Sun, Moon, planets and motion complicated by “retrograde”
150 CE Ptolemy of Alexandria stars were all spinning around loops in which they slowed and
uses mathematics to describe Earth at different rates? This temporarily reversed the general
a geocentric (Earth-centered) system appears to have been direction of their motion.
model of the universe. widely accepted in the ancient
world, and became entrenched in Ptolemaic system
AFTER classical philosophy through the To explain these complications,
1609 Johannes Kepler resolves works of Plato and Aristotle in Greek astronomers introduced
the outstanding conflicts in the the 4th century BCE. the idea of epicycles—“sub-orbits”
heliocentric (Sun-centered) around which the planets circled
model of the solar system by However, when the ancient as the central “pivot” points of the
proposing elliptical orbits. Greeks measured the movements
of the planets, it became clear
1610 After observing the that the geocentric system had
moons of Jupiter, Galileo problems. The orbits of the known
becomes convinced that planets—five wandering lights in
Copernicus was right. the sky—followed complex paths.
Mercury and Venus were always
seen in the morning and evening
skies, describing tight loops around

Earth appears to be Placing the Sun at the center
stationary, with the Sun, Moon, produces a far more elegant model,
with Earth and the planets orbiting the Sun,
planets, and stars orbiting it. and the stars a huge distance away.

However, a model of the At the center of
universe with Earth at its center everything is the Sun.
cannot describe the movement of
the planets without using a very

complicated system.

SCIENTIFIC REVOLUTION 37

See also: Zhang Heng 26–27 ■ Johannes Kepler 40–41 ■ Galileo Galilei 42–43 ■ William Herschel 86–87 ■
Edwin Hubble 236–41

sub-orbits were carried around Empire dwindled in subsequent to attempt ever more accurate
the Sun. This system was best centuries, the Christian Church measurements of the motions
refined by the great Greco-Roman inherited many of its assumptions. of the planets.
astronomer and geographer Ptolemy The idea that Earth was the center
of Alexandria in the 2nd century CE. of everything, and that man was Arabic scholarship
the pinnacle of God’s creation, The later centuries of the first
Even in the classical world, with dominion over Earth, became millennium corresponded with
however, there were differences a central tenet of Christianity and the first great flowering of Arabic
of opinion—the Greek thinker held sway in Europe until the science. The rapid spread of
Aristarchus of Samos, for instance, 16th century. Islam across the Middle East
used ingenious trigonometric and North Africa from the 7th
measurements to calculate the However, this does not mean century brought Arab thinkers
relative distances of the Sun and that astronomy stagnated for into contact with classical texts,
Moon in the 3rd century BCE. He a millennium and a half after including the astronomical
found that the Sun was huge, and Ptolemy. The ability to accurately writings of Ptolemy and others.
this inspired him to suggest that predict the movements of the
the Sun was a more likely pivot planets was not only a scientific The practice of “positional
point for the motion of the cosmos. and philosophical puzzle, but also astronomy”—calculating the
had supposed practical purposes positions of heavenly bodies—
However, the Ptolemaic system thanks to the superstitions of reached its apogee in Spain,
ultimately won out over rival astrology. Stargazers of all which had become a dynamic
theories, with far-reaching persuasions had good reason melting pot of Islamic, Jewish,
implications. While the Roman and Christian thought. In the late
13th century, King Alfonso X of
Sun Castile sponsored the compilation
of the Alfonsine Tables, which
Mars combined new observations with
centuries of Islamic records to
Mercury bring new precision to the
Ptolemaic system and provide
Earth Venus the data that would be used to
Moon calculate planetary positions
until the early 17th century.
Jupiter
Questioning Ptolemy
Saturn However, by this point the
Ptolemy’s model of the universe has Earth unmoving at the center, Ptolemaic model was becoming
with the Sun, Moon, and the five known planets following circular absurdly complicated, with yet
orbits around it. To make their orbits agree with observations, Ptolemy more epicycles added to keep
added smaller epicycles to each planet’s movement. prediction in line with observation.
In 1377, French philosopher
Nicole Oresme, Bishop of Lisieux,
addressed this problem head-on in
the work Livre du Ciel et du Monde
(Book of the Heavens and the
Earth). He demonstrated the lack
of observational proof that Earth
was static, and argued that there
was no reason to suppose that it ❯❯

38 NICOLAUS COPERNICUS

was not in motion. Yet, despite motions on certain parts of their This 17th-century illustration of the
his demolition of the evidence for orbits. One important implication Copernican system shows the planets
the Ptolemaic system, Oresme of his model was that it vastly in circular orbits around the Sun.
concluded that he did not himself increased the size of the universe. If Copernicus believed that the planets
believe in a moving Earth. Earth was moving around the Sun, were attached to heavenly spheres.
then this should give itself away
By the beginning of the 16th through parallax effects caused by It was Rheticus who published
century, the situation had become our changing point of view: the the first widely circulated account
very different. The twin forces of the stars should appear to shift back of the Copernican system, known
Renaissance and the Protestant and forth across the sky throughout as the Narratio Prima, in 1540.
Reformation saw many old religious the year. Because they do not do so, Rheticus urged the aging priest
dogmas opened up to question. It they must be very far away indeed. to publish his own work in full—
was in this context that Nicolaus something that Copernicus had
Copernicus, a Polish Catholic canon The Copernican model soon contemplated for many years, but
from the province of Warmia, put proved itself far more accurate than only conceded to in 1543 as he
forward the first modern heliocentric any refinement of the old Ptolemaic lay on his deathbed.
theory, shifting the center of the system, and word spread among
universe from Earth to the Sun. intellectual circles across Europe. Mathematical tool
Notice even reached Rome, where, Published posthumously, De
Copernicus first published his contrary to popular belief, the Revolutionibus Orbium Coelestium
ideas in a short pamphlet known model was at first welcomed in (On the Revolutions of the Heavenly
as the Commentariolus, circulated some Catholic circles. The new Spheres) was not initially greeted
among friends from around 1514. model caused enough of a stir for with outrage, even though any
His theory was similar in essence German mathematician Georg suggestion that Earth was in motion
to the system proposed by Joachim Rheticus to travel to directly contradicted several
Aristarchus, and while it overcame Warmia and become Copernicus’s passages of Scripture and was
many of the earlier model’s failings, pupil and assistant from 1539.
it remained deeply attached to
certain pillars of Ptolemaic
thought—most significantly the
idea that the orbits of celestial
objects were mounted on
crystalline spheres that rotated in
perfect circular motion. As a result,
Copernicus had to introduce
“epicycles” of his own in order to
regulate the speed of planetary

Since the Sun remains
stationary, whatever appears
as a motion of the Sun is due

to the motion of the Earth.
Nicolaus Copernicus

SCIENTIFIC REVOLUTION 39

therefore regarded as heretical As though seated on a Nicolaus Copernicus
by both Catholic and Protestant royal throne, the Sun
theologians. To sidestep the issue, governs the family of planets Born in the Polish city of
a preface had been inserted that revolving around it. Torun in 1473, Nicolaus
explained the heliocentric model Nicolaus Copernicus Copernicus was the youngest
as purely a mathematical tool for of four children of a wealthy
prediction, not a description of Church, thanks largely to the merchant. His father died
the physical universe. In his life, controversy surrounding Italian when Nicolaus was 10. An
however, Copernicus himself scientist Galileo Galilei. Galileo’s uncle took him under his wing
had shown no such reservations. 1610 observations of the phases and oversaw his education at
Despite its heretical implications, displayed by Venus and the the University of Krakow. He
the Copernican model was used presence of moons orbiting Jupiter spent several years in Italy
for the calculations involved in the convinced him that the heliocentric studying medicine and law,
great calendar reform introduced theory was correct, and his ardent returning in 1503 to Poland,
by Pope Gregory XIII in 1582. support for it, from the heart of where he joined the canonry
Catholic Italy, was ultimately under his uncle, who was now
However, new problems with expressed in his Dialogue Prince-Bishop of Warmia.
the model’s predictive accuracy Concerning the Two Chief World
soon began to emerge, thanks to Systems (1632). This led Galileo Copernicus was a master
the meticulous observations of the into conflict with the papacy, of both languages and
Danish astronomer Tycho Brahe one result of which was the mathematics, translating
(1546–1601), which showed that retrospective censorship of several important works and
the Copernican model did not controversial passages in De developing ideas about
adequately describe planetary Revolutionibus in 1616. This economics, as well as working
motions. Brahe attempted to prohibition would not be lifted on his astronomical theories.
resolve these contradictions with for more than two centuries. ■ The theory he outlined in
a model of his own in which the De Revolutionibus was
planets went around the Sun but daunting in its mathematical
the Sun and Moon remained in complexity, so while many
orbit around Earth. The real recognized its significance,
solution—that of elliptical orbits— it was not widely adopted
would only be found by his pupil by astronomers for practical
Johannes Kepler. everyday use.

It would be six decades before Key works
Copernicanism became truly
emblematic of the split caused in 1514 Commentariolus
Europe by the Reformation of the 1543 De Revolutionibus
Orbium Coelestium (On
Earth in As Earth moves around the Sun, the apparent the Revolutions of the
January position of stars at different distances changes Heavenly Spheres)
due to an effect called parallax. Since the stars are
so far away, the effect is small and can only be
detected using telescopes.

Sun Near
Earth in July star
Apparent position
Distant stars

40

THE ORBIT OF
EVERY PLANET
IS AN ELLIPSE

JOHANNES KEPLER (1571–1630)

IN CONTEXT W hile the work of Nicolaus stated that the planets orbited the
Copernicus on celestial Sun on perfect circular paths, and
BRANCH orbits, published in was forced to introduce a variety
Astronomy 1543, made a convincing case for a of complications to his model to
heliocentric (Sun-centered) model account for their irregularities.
BEFORE of the universe, his system suffered
150 CE Ptolemy of Alexandria from significant problems. Unable Supernova and comets
publishes the Algamest, a to break free from ancient ideas In the latter half of the 16th century,
model of the universe built that heavenly bodies were mounted Danish nobleman Tycho Brahe
on the assumption that Earth on crystal spheres, Copernicus had (1546–1601) made observations that
lies at its center and the
Sun, Moon, planets and The birth of a new Observations of comets
stars revolve around it in star in a constellation show that they move
circular orbits on fixed shows that the heavens among the planets,
celestial spheres. beyond the planets are crossing their orbits.

16th century The idea of not unchanging.
a Sun-centered cosmology
begins to gain followers If the planets are not This suggests
through the ideas of fixed onto spheres, an that heavenly bodies are
Nicolaus Copernicus. elliptical orbit around the not attached to fixed
Sun best explains their
AFTER observed motion. celestial spheres.
1639 Jeremiah Horrocks uses
Kepler’s ideas to predict and The orbit of every
view a transit of Venus across planet is an ellipse.
the face of the Sun.

1687 Isaac Newton’s laws of
motion and gravitation reveal
the physical principles that
give rise to Kepler’s laws.

SCIENTIFIC REVOLUTION 41

See also: Nicolaus Copernicus 34–39 ■ Jeremiah Horrocks 52 ■
Isaac Newton 62–69

would prove vital to resolving the than truly circular. Kepler Johannes Kepler
problems. A bright supernova formulated a heliocentric model
explosion seen in the constellation with ovoid orbits, but this still did Born in the city of Weil der
of Cassiopeia in 1572 undermined not match the observational data. Stadt near Stuttgart, southern
the Copernican idea that the In 1605, he concluded that Mars Germany, in 1571, Johannes
universe beyond the planets was must instead orbit the Sun in an Kepler witnessed the Great
unchanging. In 1577, Brahe plotted ellipse—a “stretched circle” with Comet of 1577 as a small
the motion of a comet. Comets the Sun as one of two focus points. child, marking the start of
had been thought of as local In his Astronomia Nova (New his fascination with the
phenomena, closer than the Moon, Astronomy) of 1609, he outlined two heavens. While studying at
but Brahe’s observations showed laws of planetary motion. The first the University of Tübingen,
that the comet must lie well beyond law stated that the orbit of every he developed a reputation as
the Moon, and was in fact moving planet is an ellipse. The second law a brilliant mathematician and
among the planets. In one stroke, stated that a line joining a planet to astrologer. He corresponded
this evidence demolished the idea the Sun sweeps across equal areas with various leading
of “heavenly spheres.” However, during equal periods of time. This astronomers of the time,
Brahe remained wedded to the idea means that the speed of the planets including Tycho Brahe,
of circular orbits in his geocentric increases the closer they are to the ultimately moving to Prague
(Earth-centered) model. Sun. A third law, in 1619, described in 1600 to become Brahe’s
the relationship of a planet’s year student and academic heir.
In 1597, Brahe was invited to to its distance from the Sun: the
Prague, where he spent his last square of a planet’s orbital period Following Brahe’s death in
years as Imperial Mathematician (year) is proportional to the cube 1601, Kepler took on the post
to Emperor Rudolph II. Here he of its distance from the Sun. So a of Imperial Mathematician,
was joined by German astrologer planet that is twice the distance with a royal commission to
Johannes Kepler, who continued from the Sun than another planet complete Brahe’s work on the
Brahe’s work after his death. will have a year that is almost so-called Rudolphine Tables
three times as long. for predicting the movements
Breaking with circles of the planets. He completed
Kepler had already begun to The nature of the force keeping this work in Linz, Austria,
calculate a new orbit for Mars from the planets in orbit was unknown. where he worked from 1612
Brahe’s observations, and around Kepler believed it was magnetic, until his death in 1630.
this time concluded that its orbit but it would be 1687 before Newton
must be ovoid (egg-shaped) rather showed that it was gravity. ■ Key works

Kepler’s laws state Focus t Focus 1596 The Cosmic Mystery
that planets follow tA A 1609 Astronomia Nova
elliptical orbits with A (New Astronomy)
the Sun as one of the t 1619 The Harmony of
two foci of the ellipse. the World
In any given time, t, Sun 1627 Rudolphine Tables
a line joining the
planets to the Sun
sweeps across
equal areas (A)
in the ellipse.

Planet

42

A FALLING BODY
ACCELERATES
UNIFORMLY

GALILEO GALILEI (1564–1642)

IN CONTEXT F or 2,000 years, few people With the equipment available
challenged Aristotle’s during the 1630s, Galileo could
BRANCH assertion that an external not directly measure the speed or
Physics force keeps things moving and that acceleration of freely falling objects.
heavy objects fall faster than lighter By rolling balls down one ramp and
BEFORE ones. Only in the 17th century up another, he showed that the
4th century BCE Aristotle did the Italian astronomer and speed of a ball at the bottom of
develops ideas about forces mathematician Galileo Galilei the ramp depended on its starting
and motion, but does not test insist that the ideas had to be height, not on the steepness of the
them experimentally. tested. He devised experiments ramp, and that a ball would always
to test how and why objects move roll up to the same height it had
1020 Persian scholar Ibn Sina and stop moving, and was the first started from, no matter how steep
(Avicenna) writes that moving to figure out the principle of or shallow the inclines were.
objects have innate “impetus,” inertia—that objects resist a
slowed only by external factors change in motion and need a force Galileo carried out his remaining
such as air resistance. to start moving, speed up, or slow experiments with a ramp 16 ft (5 m)
down. By timing objects falling, long, lined with a smooth material to
1586 Flemish engineer Simon Galileo showed that the rate of fall reduce friction. For timing, he used a
Stevin drops two lead balls of is the same for all objects, and large container of water with a small
unequal weight from a church came to realize the part played by pipe in the bottom. He collected the
tower in Delft to show that friction in slowing them down. water during the interval he was
they fall at the same speed. measuring, and weighed the water

AFTER Galileo demonstrated that the speed a ball
1687 Isaac Newton’s Principia
formulates his laws of motion. reaches at the bottom of a ramp depends only on

1971 US astronaut Dave Scott A its starting height, not the steepness of the ramp. B
demonstrates Galileo’s ideas Here, balls dropped from points A and B will
about falling bodies by
showing that a hammer and a reach the bottom of the ramp at the same speed.
feather fall at the same rate on
the Moon, which has almost
no atmosphere to cause drag.

SCIENTIFIC REVOLUTION 43

See also: Nicolaus Copernicus 34–39 ■ Isaac Newton 62–69

Count what is countable, needs a bigger force to make it Objects of different
measure what is measurable, accelerate. The two effects cancel masses appear to fall at
and what is not measurable, each other out, so in the absence of
any other forces, all falling objects different rates.
make it measurable. will accelerate at the same rate. We
Galileo Galilei see things falling at different rates All moving objects are
in everyday life because of the affected by air resistance.
collected. By letting the ball go at effect of air resistance, which slows
different points on the ramp, he objects down at different rates Without air resistance,
showed that the distance traveled depending on their size and shape. all objects would fall at
depended on the square of the time A beach ball and a bowling ball the same rate.
taken—in other words, the ball of the same size will initially
accelerated down the ramp. accelerate at the same rate. Once A falling body
they are moving, the same amount accelerates
The law of falling bodies of air resistance will act on them, uniformly.
Galileo’s conclusion was that bodies but the size of this force will be a
all fall at the same speed in a much greater proportion of the
vacuum, an idea later developed downward force on the beach ball
further by Isaac Newton. There is a than the bowling ball, and so the
greater force from gravity on a larger beach ball will slow down more.
mass, but the larger mass also
Galileo’s insistence on testing
theories with careful observation
and measurable experiments marks
him, like Alhazen, as one of the
founders of modern science. His
ideas on forces and motion paved
the way for Newton’s laws of motion
50 years later and underpin our
understanding of movement in the
universe, from atoms to galaxies. ■

Galileo Galilei Galileo was born in Pisa, but made to recant this and other
later moved with his family to ideas. He was sentenced to
Florence. In 1581, he enrolled house arrest, which lasted
in the University of Pisa to the rest of his life. During
study medicine, then switched his confinement, he wrote a
to mathematics and natural book summarizing his work
philosophy. He investigated many on kinematics (the science
areas of science, and is perhaps of movement).
most famous for his discovery of
the four largest moons of Jupiter Key works
(still called the Galilean moons).
Galileo’s observations led him to 1623 The Assayer 
support the Sun-centered model 1632 Dialogue Concerning the
of the solar system, which at Two Chief World Systems 
the time was in opposition to the 1638 Discourses and
teachings of the Roman Catholic Mathematical Demonstrations
Church. In 1633, he was tried and Relating to Two New Sciences 

44

THE GLOBE
OF THE EARTH
IS A MAGNET

WILLIAM GILBERT (1544–1603)

IN CONTEXT B y the late 1500s, ships’ Gilbert’s breakthrough came not
captains already relied on from a flash of inspiration, but from
BRANCH magnetic compasses to 17 years of meticulous experiment.
Geology maintain their course across the He learned all he could from ships’
oceans. Yet no one knew how they captains and compass makers, and
BEFORE worked. Some thought the compass then he made a model globe, or
6th century BCE The Greek needle was attracted to the North “terrella,” out of the magnetic rock
thinker Thales of Miletus notes Star, others that it was drawn to lodestone and tested compass
magnetic rocks, or lodestones. magnetic mountains in the Arctic. needles against it. The needles
It was English physician William reacted around the terrella just as
1st century CE Chinese Gilbert who discovered that Earth ships’ compasses did on a larger
diviners make primitive itself is magnetic. scale—showing the same patterns
compasses with iron ladles of declination (pointing slightly
that swivel to point south. Stronger reasons are obtained away from true north at the
from sure experiments and geographic pole, which differs from
1269 French scholar Pierre de demonstrated arguments magnetic north) and inclination
Maricourt sets out the basic than from probable (tilting down from the horizontal
laws of magnetic attraction, conjectures and the opinions toward the globe).
repulsion, and poles. of philosophical speculators.
William Gilbert Gilbert concluded, rightly, that
AFTER the entire planet is a magnet and
1824 French mathematician has a core of iron. He published
Siméon Poisson models the his ideas in the book De Magnete
forces in a magnetic field. (On the Magnet) in 1600, causing
a sensation. Johannes Kepler and
1940s American physicist Galileo, in particular, were inspired
Walter Maurice Elsasser by his suggestion that Earth is not
attributes Earth’s magnetic fixed to rotating celestial spheres,
field to iron swirling in its outer as most people still thought, but is
core as the planet rotates. made to spin by the invisible force
of its own magnetism. ■
1958 Explorer 1 space mission
shows Earth’s magnetic field See also: Thales of Miletus 20 ■ Johannes Kepler 40–41 ■ Galileo Galilei 42–43 ■
extending far out into space. Hans Christian Ørsted 120 ■ James Clerk Maxwell 180–85

SCIENTIFIC REVOLUTION 45

NOT BY ARGUING,
BUT BY TRYING

FRANCIS BACON (1561–1626)

IN CONTEXT T he English philosopher, Whether or no anything can
statesman, and scientist be known, can be settled not
BRANCH Francis Bacon was not
Experimental science the first to conduct experiments— by arguing, but by trying.
Alhazen and other Arab scientists Francis Bacon
BEFORE conducted them 600 years earlier—
4th century BCE Aristotle but he was the first to explain the
deduces, argues, and writes, methods of inductive reasoning and
but does not test with set out the scientific method. He
experiments—his methods also saw science as a “spring of a
persist for the next millennium. progeny of inventions, which shall
overcome, to some extent, and
c.750–1250 CE Arab scientists subdue our needs and miseries.”
conduct experiments during
the Golden Age of Islam. Evidence from experiment scientific method: observation,
According to the Greek philosopher deduction to formulate a theory
AFTER Plato, truth was found by authority that might explain what has been
1630s Galileo experiments and argument—if enough intelligent observed, and experiment to test
with falling bodies. men discussed something for long whether the theory is correct. In
enough, the truth would result. His The New Atlantis (1623), Bacon
1637 French philosopher René student, Aristotle, saw no need for describes a fictitious island and
Descartes insists on rigorous experiments. Bacon parodied such its House of Salomon—a research
scepticism and inquiry in his “authorities” as spiders, spinning institution where scholars conduct
Discourse on Method. webs from their own substance. He pure research centered on
insisted on evidence from the real experiment and make inventions.
1665 Isaac Newton uses a world, particularly from experiment. Sharing those goals, the Royal
prism to investigate light. Society was founded in 1660 in
Two key works by Bacon laid London, with Robert Hooke as its
1963 In Conjectures and out the future of scientific inquiry. first Curator of Experiments. ■
Refutations, the Austrian In Novum Organum (1620), he sets
philosopher Karl Popper insists out his three fundamentals for the
that a theory may be tested
and proved false, but cannot See also: Alhazen 28–29 ■ Galileo Galilei 42–43 ■ William Gilbert 44 ■
conclusively be proved correct. Robert Hooke 54 ■ Isaac Newton 62–69

46 IN CONTEXT

TOUCHING BRANCH
THE SPRING Physics
OF THE AIR
BEFORE
ROBERT BOYLE (1627–1691) 1643 Evangelista Torricelli
invents the barometer using
a tube of mercury.

1648 Blaise Pascal and his
brother-in-law demonstrate
that air pressure decreases
with altitude.

1650 Otto von Guericke
performs experiments
on air and vacuums, first
published in 1657.

AFTER
1738 Swiss physicist
Daniel Bernoulli publishes
Hydrodynamica, describing
a kinetic theory of gases.

1827 Scottish botanist Robert
Brown explains the motion
of pollen in water as a result of
collisions with water molecules
moving in random directions.

I n the 17th century, several
scientists across Europe
investigated the properties
of air, and their work was to lead
Anglo-Irish scientist Robert Boyle
to produce his mathematical laws
describing pressure in a gas. This
work was tied in to a wider debate
about the nature of the space
between stars and planets. The
“atomists” held that there was
empty space between celestial
bodies, whereas the Cartesians
(followers of the French philosopher
René Descartes) held that the space
between particles was filled with
an unknown substance called the
ether, and that it was impossible to
produce a vacuum.

SCIENTIFIC REVOLUTION 47

See also: Isaac Newton 62–69 ■ John Dalton 112–13 ■ Robert FitzRoy 150–55

Torricellian vaccum The barometer
invented by
We live submerged at the Mercury Scale Evangelista Torricelli
bottom of an ocean of Tube used a column of
the element air, that by Pressure of mercury to measure
mercury column air pressure. Torricelli
unquestioned experiments correctly reasoned
is known to have weight. Pressure of that it was the air
Evangelista Torricelli atmosphere pressing down on
the mercury in the
cistern that balanced
the column of
mercury in the tube.

Barometers He said that the space in the tube Cistern (dish)
In Italy, the mathematician Gasparo above the mercury was a vacuum.
Berti performed experiments This is explained today in terms to demonstrate that air pressure
designed to figure out why a of pressure (force on a certain area), changed depending on altitude.
suction pump could not raise water but the basic idea is the same. One barometer was set up on
more than 33 ft (10 m) high. Berti Torricelli had invented the first the grounds of a monastery in
took a long tube, sealed it at one mercury barometer. Clermont, and observed by a monk
end and filled it with water. He then during the day. Périer carried the
inverted the tube with its mouth in French scientist Blaise Pascal other to the top of Puy de Dôme,
a tub of water. The level of water heard of Torricelli’s barometer about 3,200 ft (1,000 m) above the
in the tube fell until the column in 1646, prompting him to start town. The column of mercury was
was about 30 ft (10 m) high. In some experiments of his own. more than 3 in (8 cm) shorter at
1642, fellow Italian Evangelista One of these, performed by his the top of the mountain than in the
Torricelli, hearing of Berti’s work, brother-in-law Florin Périer, was monastery garden. Since there is
constructed a similar apparatus less air above a mountain than
but used mercury instead of water. there is above the valley below
Mercury is more than 13 times it, this showed that it was indeed
denser than water, so his column the weight of the air that held the
of liquid was only about 30 in liquid in the tubes of mercury or
(76 cm) high. Torricelli’s explanation water. For this, and other work,
for this was that the weight of the the modern unit of pressure is
air above the mercury in the dish named after Pascal.
was pressing down on it, and that
this balanced the weight of the Air pumps
mercury inside the column. The next important breakthrough
was made by Prussian scientist
Blaise Pascal’s experiments with Otto von Guericke, who made a
barometers showed how air pressure pump that was capable of pumping
varied with altitude. In addition to some of the air out of a container.
physics, Pascal also made significant He performed his most famous ❯❯
contributions to mathematics.

48 ROBERT BOYLE

Men are so accustomed to experiments of his own, Boyle he was intent on pointing out that
judge of things by their senses commissioned Robert Hooke (p.54) the results described are all from
to design and build an air pump. experiments, since at the time even
that, because the air is Hooke’s air pump consisted of a such noted experimentalists as
indivisible, they ascribe but glass “receiver” (container) whose Galileo often also reported the
little to it, and think it but diameter was nearly 16 in (40 cm), results of “thought experiments.”
one remove from nothing. a cylinder with a piston below it,
and an arrangement of plugs Many of Boyle’s experiments
Robert Boyle and valves between them. were directly connected to air
Successive movements of the pressure. The receiver could be
demonstration in 1654, when he put piston drew more and more air out modified to hold a Torricelli
two metal hemispheres together of the receiver. Due to slow leaks barometer, with the tube sticking
with an airtight seal between them in the seals of the equipment, the
and pumped the air out of them— near-vacuum inside the receiver
two teams of horses were unable could only be maintained for a
to pull the hemispheres apart. short time. Nevertheless, the
Before the air was pumped out, machine was a great improvement
the air pressure inside the sealed on anything made previously, an
hemispheres was the same as the example of the importance of
air pressure outside. Without the air technology to the furthering
inside, pressure from the outside of scientific investigation.
air held the hemispheres together.
Experimental results
Robert Boyle learned of von Boyle performed a number of
Guericke’s experiments when they different experiments with the
were published in 1657. To do air pump, which he described in
his 1660 book New Experiments
Physico-Mechanical. In the book,

Otto von Guericke built the first air
pump. His experiments with the pump
provided evidence against Aristotle’s
idea that “Nature abhors a vacuum.”

Robert Boyle Robert Boyle was born in Ireland, to discuss their ideas. This
the 14th child of the Earl of Cork. group became the Royal Society
He was tutored at home before in 1663, and Boyle was one
attending Eton College in England of the first council members.
and then touring Europe. His In addition to his interests
father died in 1643, leaving him in science, Boyle performed
enough money to indulge his experiments in alchemy and
interest in science full time. Boyle wrote about theology and the
moved back to Ireland for a couple origin of different human races.
of years, but lived in Oxford from
1654 to 1668 so that he could do Key works
his work more easily, and then
moved to London. 1660 New Experiments
Physico-Mechanical:
Boyle was part of a group of Touching the Spring of the
men studying scientific subjects Air and their Effects
called the “Invisible College,” 1661 The Sceptical Chymist
who met in London and Oxford