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LONDON, NEW YORK, MELBOURNE, MUNICH, AND DELHI DK LONDON produced for DK by Published in the United States by DK Publishing PROJECT ART EDITOR TALL TREE LTD. Katie Cavanagh 4th floor, 345 Hudson Street EDITORS New York, New York 10014 SENIOR EDITOR Rob Colson Georgina Palffy Camilla Hallinan 14 15 16 17 18 10 9 8 7 6 5 4 3 2 1 David John 001–192893–July/2014 US EDITOR DESIGN AND ART DIRECTION Jane Perlmutter Ben Ruocco Copyright © 2014 Dorling Kindersley Limited US SENIOR EDITOR DK DELHI Margaret Parrish All rights reserved PROJECT EDITOR MANAGING ART EDITOR Priyaneet Singh Without limiting the rights under Lee Griffiths copyright reserved above, no part ASSISTANT ART EDITOR of this publication may be reproduced, MANAGING EDITOR Vidit Vashisht stored in or introduced into a retrieval Stephanie Farrow system, or transmitted, in any form, or DTP DESIGNER by any means (electronic, mechanical, PUBLISHING DIRECTOR Jaypal Chauhan photocopying, recording, or otherwise), Jonathan Metcalf without the prior written permission MANAGING EDITOR of both the copyright owner and the ART DIRECTOR Kingshuk Ghoshal Phil Ormerod above publisher of this book. MANAGING ART EDITOR PUBLISHER Govind Mittal Published in Great Britain by Andrew Macintyre Dorling Kindersley Limited PREPRODUCTION MANAGER JACKET DESIGNER Balwant Singh A catalog record for this book is Laura Brim available from the Library of Congress. original styling by JACKET EDITOR ISBN: 978-1-4654-1965-1 Maud Whatley STUDIO 8 DK books are available at special JACKET DESIGN discounts when purchased in bulk for DEVELOPMENT MANAGER sales promotions, premiums, fund-raising, or educational use. For details, contact: Sophia MTT DK Publishing Special Markets, 345 Hudson Street, New York, New York PREPRODUCTION PRODUCER Adam Stoneham 10014 or [email protected]. PRODUCER Printed and bound in China Mandy Inness by Leo Paper Products Ltd. ILLUSTRATIONS Discover more at James Graham, Peter Liddiard www.dk.com

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