dk-the-science-book_compress

SCIENTIFIC REVOLUTION 49 out of the top of the receiver and The height of mercury The level of mercury falls sealed in place with cement. As in a barometer falls if as air is pumped out of the the pressure in the receiver was you take the barometer reduced, the level of the mercury up a mountain. receiver in a barometer. fell. He also performed the opposite experiment, and found that raising This is because there is This means that the the pressure inside the receiver less air above you smaller the amount of made the level of the mercury rise. pressing down This confirmed the previous on the mercury. air in the receiver, the findings of Torricelli and Pascal. lower its pressure. Boyle noted that it became The “spring of the air” decreases as harder and harder to pump air out the mass of the air decreases. of the receiver as the amount of air left decreased, and also showed remarkably similar to the modern Power, who performed a series that a half-inflated bladder in the kinetic theory, which describes of experiments with a Torricelli receiver increased in volume as the properties of matter in terms barometer and published their the air surrounding it was removed. of moving particles. results in 1663. Boyle saw an early A similar effect on the bladder draft of the book and discussed could be achieved by holding it in Some of Boyle’s experiments the results with Towneley. He front of a fire. He gave two possible were physiological, investigating confirmed them by experiment explanations for the “spring” of the effects on birds and mice of and published “Mr Towneley’s the air that caused these effects: reducing the pressure of the hypothesis” in 1662 as part of each particle of the air was air, and speculating on how air a response to criticism of his compressible like a spring and the is moved in and out of lungs. original experiments. whole mass of air resembled fleece, or the air consisted of particles Boyle’s law Boyle’s work on gases was moving randomly. Boyle’s law states that the pressure particularly significant because of of a gas multiplied by its volume his careful experimental technique, This was similar to the view is a constant, as long as the amount and also his full reporting of all his of the Cartesians, although Boyle of gas and the temperature are experiments and their possible did not agree with the idea of kept the same. In other words, if sources of error, whether or not the ether, but suggested that the you decrease the volume of a gas, they gave the expected results. “corpuscles” were moving in its pressure increases. It is this This led many to seek to extend his empty space. His explanation is increased pressure that produces work. Today, Boyle’s law has been the spring of the air. You can feel combined with laws figured out by If the height of the mercury this effect using a bicycle pump other scientists to form the “ideal- column is less on the top of a by covering the end with a finger gas law,” which approximates to mountain than at the foot of it, and pushing the handle in. the behavior of real gases under it follows that the weight of the changes of temperature, pressure, air must be the sole cause of Although it bears his name, or volume. His ideas would also this law was first proposed not by eventually lead to the development the phenomenon. Boyle, but by English scientists of the kinetic theory. ■ Blaise Pascal Richard Towneley and Henry

50 IS LIGHT A PARTICLE OR A WAVE? CHRISTIAAN HUYGENS (1629–1695) IN CONTEXT Huygens thought that… Newton thought that… space is filled with an ether. a source of light emits large BRANCH numbers of tiny “corpuscles.” Physics Light is disturbances in The corpuscles are BEFORE the ether spreading weightless and travel 11th century Alhazen out as waves. shows that light travels in straight lines. in straight lines. Is light a particle or a wave? 1630 René Descartes proposes a wave description of light. I n the 17th century, Isaac is the bending of light as it passes Newton and the Dutch from one substance to another, and 1660 Robert Hooke states astronomer Christiaan is the reason that lenses can focus that light is a vibration of Huygens both pondered the true light. Diffraction is the spreading the medium through which nature of light, and reached very out of light when it passes through it propagates. different conclusions. The problem a very narrow gap. they faced was that any theory AFTER about the nature of light had to Before Newton’s experiments, 1803 Thomas Young describes explain reflection, refraction, it was widely accepted that light experiments that demonstrate diffraction, and color. Refraction gained its quality of color by how light behaves as a wave. interacting with matter—that 1864 James Clerk Maxwell predicts the speed of light and concludes that light is a form of electromagnetic wave. 1900s Albert Einstein and Max Planck show that light is both a particle and a wave. The quanta of electromagnetic radiation they recognize become known as “photons.”

SCIENTIFIC REVOLUTION 51 See also: Alhazen 28–29 ■ Robert Hooke 54 ■ Isaac Newton 62–69 ■ Thomas Young 110–11 ■ James Clerk Maxwell 180–85 ■ Albert Einstein 214–21 the “rainbow” effect seen when spread out in spherical waves. When white light passes through a light passes through a prism is Refraction was thus explained prism, it is refracted into its component produced because the prism has if different materials (be they ether, parts. Huygens explained that this is somehow stained the light. Newton water, or glass) caused light waves due to light waves traveling at different demonstrated that the “white” light to travel at different speeds. speeds through different materials. that we see is actually a mixture of Huygens’ theory could explain why different colors of light, and these both reflection and refraction can century later, in 1803, Thomas are split up by a prism because occur at a surface. It could also Young showed that light does they are all refracted by slightly explain diffraction. indeed behave as a wave, and different amounts. experiments in the 20th century Huygens’ ideas made little have shown that it behaves both As with many natural impact at the time. This was in like a wave and a particle, although philosophers of the time, Newton part due to Newton’s already giant there are big differences between held that light was made up of a stature as a scientist. However, a Huygens’ “spherical waves” and stream of particles, or “corpuscles.” our modern models of light. This idea explained how light Huygens said that light waves were traveled in straight lines and longitudinal as they passed through “bounced” off reflective surfaces. It a substance—the ether. Sound also explained refraction in terms of waves are also longitudinal waves, forces at the boundaries between in which the particles of the different materials. substance the wave is passing through vibrate in the same Partial reflection direction as the wave is traveling. However, Newton’s theory could Our modern view of light waves is not explain how, when light hits that they are transverse waves that many surfaces, some is reflected behave more like waves of water. and some is refracted. In 1678, They do not need matter to Huygens argued that space was propagate (transmit), while particles filled with weightless particles vibrate at right angles (up and (the ether), and that light caused down) to the wave’s direction. ■ disturbances in the ether that Christiaan Huygens Dutch mathematician and the force of gravity. Huygens’ astronomer Christiaan Huygens wide-ranging achievements was born in The Hague in 1629. included some of the most He studied law and mathematics accurate clocks of his time, the at his university, then devoted result of his work on pendulums. some time to his own research, His astronomical work, carried initially in mathematics but then out using his own telescopes, also in optics, working on included the discovery of Titan, telescopes and grinding his the largest of Saturn’s moons, own lenses. and the first correct description of Saturn’s rings. Huygens visited England several times, and met Isaac Key works Newton in 1689. In addition to his work on light, Huygens had 1656 De Saturni Luna studied forces and motion, but he Observatio Nova did not accept Newton’s idea of 1690 Treatise on Light “action at a distance” to describe

52 THE FIRST OBSERVATION OF A TRANSIT OF VENUS JEREMIAH HORROCKS (1618–1641) IN CONTEXT P lanetary transits offered I received my first an opportunity to test the intimation of the remarkable BRANCH first of Johannes Kepler’s conjunction of Venus and the Astronomy three laws of planetary motion— that the planets orbit the Sun in an Sun…it induced me, in BEFORE elliptical path. The brief passages expectation of so grand a 1543 Nicolaus Copernicus by Venus and Mercury across spectacle, to observe with makes the first complete the disk of the Sun—at the times argument for a Sun-centered predicted by Kepler’s Rudolphine increased attention. (heliocentric) universe. Tables—would reveal whether the Jeremiah Horrocks underlying theory was correct. 1609 Johannes Kepler marked its progress on the card, proposes a system of The first test—a 1631 transit timing each interval, a friend elliptical orbits—the first of Mercury observed by French measured the transit in another complete description of astronomer Pierre Gassendi— location. By using the two sets of planetary motion. proved encouraging. However, measurements from the different his attempt to spot the transit of viewpoints, and by recalculating AFTER Venus a month later failed due the diameter of Venus relative to the 1663 Scottish mathematician to inaccuracies in Kepler’s figures. Sun, Horrocks could then estimate James Gregory devises a way These same figures predicted a Earth’s distance from the Sun more to measure the exact distance “near miss” for Venus and the Sun accurately than ever before. ■ from Earth to the Sun using in 1639, but English astronomer observations of the transits of Jeremiah Horrocks calculated that Venus in 1631 and 1639. a transit would in fact occur. 1769 British explorer Captain At sunrise on December 4, 1639, James Cook observes and Horrocks set up his best telescope, records the transit of Venus focusing the Sun’s disk onto a piece in Tahiti in the South Pacific. of card. Around 3:15 pm, the clouds cleared, revealing a “spot of unusual 2012 Astronomers observe magnitude”—Venus—edging the last transit of Venus across the Sun. While Horrocks of the 21st century. See also: Nicolaus Copernicus 34–39 ■ Johannes Kepler 40–41

SCIENTIFIC REVOLUTION 53 ORGANISMS DEVELOP IN A SERIES OF STEPS JAN SWAMMERDAM (1637–1680) IN CONTEXT T he metamorphosis of organism took its fully mature form a butterfly from egg to in its miniscule beginning, but that BRANCH caterpillar to chrysalis to “lower” animals were too simple to Biology adult is a familiar process to us have complex innards. In 1669, today, but in the 17th century, pioneering Dutch microscopist Jan BEFORE reproduction was viewed very Swammerdam disproved Aristotle c.320 BCE Aristotle declares differently. Following the Greek by dissecting insects under the that worms and insects arise philosopher Aristotle, most people microscope, including butterflies, by spontaneous generation. believed that life—especially dragonflies, bees, wasps, and ants. “lower” creatures such as insects— 1651 English physician William arose by spontaneous generation A new metamorphosis Harvey considers the insect from nonliving matter. The theory The term “metamorphosis” had larva a “crawling egg” and the of “preformism” held that a “higher” once meant the death of one pupa a “second egg” with little individual followed by another’s internal development. In the anatomy of a louse, you appearance from its remains. will find miracles heaped on Swammerdam showed that the 1668 Italian Francesco Redi stages in an insect’s life cycle— provides early evidence to miracles and will see the adult female, egg, larva and pupa refute spontaneous generation. wisdom of God clearly (or nymph), adult—are different forms of the same creature. Each AFTER manifested in a minute point. life stage has its own fully formed 1859 Charles Darwin explains Jan Swammerdam internal organs, as well as early how each stage of an insect’s versions of the organs for later life is adapted to its activity stages. Seen in this new light, and environment at that stage. insects clearly warranted further scientific study. Swammerdam 1913 Italian zoologist Antonio went on to pioneer the classification Berlese proposes that an insect of insects based on their larva hatches at a premature reproduction and development, stage of embryo development. before dying of malaria at 43. ■ 1930s British entomologist See also: Robert Hooke 54 ■ Antonie van Leeuwenhoek 56–57 ■ Vincent Wigglesworth finds John Ray 60–61 ■ Carl Linnaeus 74–75 ■ Louis Pasteur 156–59 hormones control life cycles.

54 ALL LIVING THINGS ARE COMPOSED OF CELLS ROBERT HOOKE (1635–1703) IN CONTEXT T he development of the crystals form and what happens compound microscope when water freezes. The English BRANCH in the 17th century diarist Samuel Pepys called Biology opened up a whole new world Micrographia “the most ingenious of previously unseen structures. book that I ever read in my life.” BEFORE A simple microscope consists of c.1600 The first compound just one lens, while the compound Describing cells microscope is developed in microscope, developed by Dutch One of Hooke’s drawings was of a the Netherlands, probably eyeglasses makers, uses two thin slice of cork. In the structure by either Hans Lippershey or or more lenses, and generally of the cork, he noted what looked Hans and Zacharius Janssen. provides greater magnification. like the walls dividing monks’ cells in a monastery. These were the first 1644 Italian priest and self- English scientist Robert Hooke recorded descriptions and drawings taught scientist Giovanni was not the first to observe living of cells, the basic units from which Battista Odierna produces things using a microscope. all living things are made. ■ the first description of living However, with the publication tissue, using a microscope. of his Micrographia in 1665, he Hooke’s drawings of dead cork cells became the first best-selling show empty spaces between the cell AFTER popular science author, stunning walls—living cells contain protoplasm. 1674 Antonie van his readers with the new science of He calculated that there were more than Leeuwenhoek is the first to see microscopy. Accurate copperplate a billion cells in 1 in3 (16 cm3) of cork. single-celled organisms under drawings made by Hooke himself the microscope. showed objects the public had never seen before—the detailed 1682 Van Leeuwenhoek anatomies of lice and fleas; the observes the nuclei inside the compound eyes of a fly; the delicate red blood cells of salmon. wings of a gnat. He also drew some man-made objects—the sharp 1931 The invention of the point of a needle appeared blunt electron microscope by under the microscope—and used Hungarian physicist Leó his observations to explain how Szilárd allows much higher resolution images to be made. See also: Antonie van Leeuwenhoek 56–57 ■ Isaac Newton 62–69 ■ Lynn Margulis 300–01

SCIENTIFIC REVOLUTION 55 LAYERS OF ROCK FORM ON TOP OF ONE ANOTHER NICOLAS STENO (1638–1686) IN CONTEXT T he sedimentary strata of Rock strata, as Steno realized, all rocks that make up much start life as horizontal layers, which BRANCH of Earth’s surface also form are subsequently deformed and Geology the basis for Earth’s geological twisted over time by huge forces history, which is normally depicted acting on them. BEFORE as a column of layers with the Late 15th century Leonardo oldest strata at the bottom and the disturbance after their deposition. da Vinci writes about his youngest at the top. The process Finally, his principle of crosscutting observations of the erosional of deposition of rock by water relationships states that “if a body and depositional action of and gravity had been known for or discontinuity cuts across a wind and water on landscapes centuries, but Danish bishop and stratum, it must have formed after and surface materials. scientist Niels Stensius, also known that stratum”. as Nicolas Steno, was the first to AFTER describe the principles that underlie Steno’s insights allowed the 1780s James Hutton the process. His conclusions, later mapping of geological strata refers Steno’s principles to published in 1669, were drawn from by the likes of William Smith in a continuing and cyclical his observations of geological strata Britain and Georges Cuvier and geological process stretching in Tuscany, Italy. Alexandre Brongniart in France. back in time. They also allowed the subdivision Steno’s Law of Superposition of strata into time-related units, 1810s Georges Cuvier and states that any single sedimentary which could be correlated with Alexandre Brongniart in deposit, or stratum, is younger than each other across the world. ■ France and William Smith the sequence of strata upon which in Britain apply Steno’s it rests, and older than the strata principles of stratigraphy that rest upon it. Steno’s principles to geological mapping. of original horizontality and lateral continuity state that strata are 1878 The first International deposited as horizontal and Geological Congress in Paris continuous layers, and if they are sets out procedures for the found tilted, folded, or broken, production of a standard they must have experienced such stratigraphic scale. See also: James Hutton 96–101 ■ William Smith 115

56 MICROSCOPIC OBSERVATIONS OF ANIMALCULES ANTONIE VAN LEEUWENHOEK (1632–1723) IN CONTEXT A ntonie van Leeuwenhoek Hooke made the first drawing of rarely ventured far from his tiny living cells that he had seen in BRANCH home above a cloth store a slice of cork through a microscope. Biology in Delft in the Netherlands. But working on his own in his back It never occurred to Hooke or BEFORE room, he discovered an entirely any other microscopist of the time 2000 BCE Chinese scientists new world—the world of previously to look for life anywhere they could make a water microscope with unseen microscopic life, including not already see it with their own a glass lens and a water-filled human sperm, blood cells, and, eyes. Van Leeuwenhoek, by tube to see very small things. most dramatically of all, bacteria. contrast, turned his lenses on places where there appeared to be 1267 English philosopher Before the 17th century, no one no life at all, particularly in liquids. Roger Bacon suggests the suspected there was life too small He studied raindrops, tooth plaque, idea of the telescope and to see with the naked eye. Fleas dung, sperm, blood, and much the microscope. were thought to be the smallest more. It was here, in these possible form of life. Then, in about c.1600 The microscope is 1600, the microscope was invented When van Leeuwenhoek’s invented in the Netherlands. by Dutch eyeglasses makers who drawings of human sperm were first put two glass lenses together to published in 1719, many people did 1665 Robert Hooke observes boost their magnification (p.54). not accept that such tiny swimming living cells and publishes In 1665, English scientist Robert “animalcules” could exist in semen. Micrographia. AFTER 1841 Swiss anatomist Albert von Kölliker finds that each sperm and egg is a cell with a nucleus. 1951 German physicist Erwin Wilhelm Müller invents the field ion microscope and sees atoms for the first time.

SCIENTIFIC REVOLUTION 57 See also: Robert Hooke 54 ■ Louis Pasteur 156–59 ■ Martinus Beijerinck 196–97 ■ Lynn Margulis 300–01 Microscopes can be turned on places where there are no visible life forms. High-magnification single-lens microscopes reveal tiny “animalcules” in water and other liquids. The world is teeming with microscopic, Antonie van single-celled life forms. Leeuwenhoek apparently lifeless substances, that thinner than a human hair in a The son of a basket maker, van Leeuwenhoek discovered the sample of lake water. These were Antonie van Leeuwenhoek richness of microscopic life. the green algae Spirogyra, an was born in Delft in 1632. example of the simple life forms After working in his uncle’s Unlike Hooke, van Leeuwenhoek that are now known as protists. linen business, he established did not use a two-lens “compound” Van Leeuwenhoek called these his own fabric store at 20 years microscope, but a single, high- tiny creatures “animalcules.” In old and remained there for the quality lens—really a magnifying October 1676, he discovered even rest of his long life. glass. At the time, it was in fact smaller single-celled bacteria in easier to produce a clear picture drops of water. In the following Van Leeuwenhoek’s with such simple microscopics. A year, he described how his own business allowed him time to magnification greater than 30 times semen was swarming with the pursue his hobby—microscopy. was impossible with compound little creatures we now call sperm. He began in about 1668 after a microscopes since the image Unlike the creatures he had found visit to London, where he may became blurred. Van Leeuwenhoek in water, the animalcules in semen have seen a copy of Robert ground his own single lens were all identical. Each of the many Hooke’s Micrographia. From microscopes, and after years of thousands he looked at had the 1673 onward, he reported his honing his technique, managed a same tiny tail and the same tiny findings in letters to the Royal magnification of more than 200 head, and nothing else, and he Society in London, writing times. His microscopes were could see them swimming like more reports to them than any small devices with tiny lenses tadpoles in the semen. scientist in history. The Royal just fractions of an inch (a few Society was initially sceptical millimeters) wide. The sample was Van Leeuwenhoek reported his of the amateur’s reports, but placed on a pin on one side of the findings in a series of hundreds Hooke repeated many of his lens, and van Leeuwenhoek held of letters to the Royal Society in experiments and confirmed his one eye up close to the other side. London. While he published his discoveries. Van Leeuwenhoek findings, he kept his lens-making made over 500 microscopes, Single-celled life techniques secret. It is probable many designed to view At first, van Leeuwenhoek found that he made his tiny lenses by specific objects. nothing unusual, but then, in 1674, fusing thin glass threads, but we he reported seeing tiny creatures do not know for sure. ■ Key works 1673 Letter 1, van Leeuwenhoek’s first letter to the Royal Society 1676 Letter 18, revealing his discovery of bacteria

58 MEASURING THE SPEED OF LIGHT OLE RØMER (1644–1710) IN CONTEXT Eclipses of Jupiter’s J upiter has many moons, moons do not always but only the four largest BRANCH match predictions. (Io, Europa, Ganymede, Astronomy and physics and Callisto) were visible through The distance between a telescope at the time that Ole BEFORE Earth and Jupiter Rømer was observing the skies 1610 Galileo Galilei of northern Europe, in the late discovers the four largest changes as the planets 17th century. These moons are moons of Jupiter. orbit the Sun. eclipsed as they pass through the shadow cast by Jupiter and 1668 Giovanni Cassini If light does not at certain times they can be publishes the first accurate propagate instantaneously, observed either entering or leaving tables predicting eclipses the shadow, depending on the of the moons of Jupiter. this explains the relative positions of Earth and discrepancies. Jupiter around the Sun. For nearly AFTER half of the year, the eclipses of 1729 James Bradley calculates The speed of the moons cannot be observed a speed of light of 185,000 light can be at all, because the Sun is between miles/s (301,000 km/s) based calculated from the Earth and Jupiter. on variations in the positions time differences of stars. and distances in the Giovanni Cassini, the director solar system. of the Royal Observatory in Paris 1809 Jean-Baptiste when Rømer started work there in Delambre uses 150 years’ the late 1660s, published a set worth of observations of of tables predicting the moons’ Jupiter’s moons to calculate eclipses. Knowing the times of a speed of light of 186,600 these eclipses provided a new miles/s (300,300 km/s). way to figure out longitude. The measurement of longitude depends 1849 Hippolyte Fizeau on knowing the difference between measures the speed of light the time at a given location and the in a laboratory, rather than time at a reference meridian (in this using astronomical data. case, Paris). On land at least, it was now possible to calculate longitude by observing the time of an eclipse

SCIENTIFIC REVOLUTION 59 See also: Galileo Galilei 42–43 ■ John Michell 88–89 ■ Léon Foucault 136–37 of one of Jupiter’s moons and Io comparing it to the predicted Jupiter time of the eclipse in Paris. It was not possible to hold a 1 telescope steadily enough onboard Earth ship to observe the eclipses, 2 and measuring longitude at sea remained impossible until John From position 1 on Earth’s orbit, the predicted Sun Harrison built the first marine eclipse of Jupitier’s moon Io appears to occur chronometers—clocks that could later than from position 2. Rømer reasoned that keep time at sea—in the 1730s. this was due to the extra distance light from Io had to travel to reach Earth in position 1. Finite or infinite speed? Rømer studied observations of calculate the speed of light. He travel instantaneously. However, the eclipses of the moon Io taken produced a figure of 133,000 miles/s not everyone agreed with over a period of two years and (214,000 km/s). The current value Rømer’s reasoning. Cassini compared these to the times is 186,282 miles/s (299,792 km/s), pointed out that discrepancies predicted by Cassini’s tables. so Rømer’s calculation was off by in the observations of the other He found a discrepancy of about 25 percent. Nevertheless, moons were still not accounted 11 minutes between observations this was an excellent first for. Rømer’s findings were not taken when Earth was closest approximation, and it solved the universally accepted until to Jupiter and those taken previously open question as to English astronomer James Bradley when it was farthest away. This whether light had a finite speed. produced his more accurate discrepancy could not be explained figure for the speed of light in by any of the known irregularities In England, Isaac Newton 1729 by measuring the parallax in the orbits of Earth, Jupiter, or readily accepted Rømer’s of stars (p.39). ■ Io. It had to be the time it took hypothesis that light did not for light to travel the diameter of Earth’s orbit. Knowing the diameter of Earth’s orbit, Rømer could now For the distance of Ole Rømer under Giovanni Cassini. In 1679, about 3,000 leagues, he visited England and met which is nearly equal Born in the Danish city of Isaac Newton. to the diameter of the Aarhus in 1644, Ole Rømer Earth, light needs not studied at the University of Returning to the University one second of time. Copenhagen. On leaving the of Copenhagan in 1681, Rømer university, he helped to prepare became professor of astronomy. Ole Rømer the astronomical observations He was involved in modernizing of Tycho Brahe for publication. weights and measures, the Rømer also made his own calendar, and building codes, observations, recording and even the water supplies. the times of the eclipses of Unfortunately, his astronomical Jupiter’s moons from Brahe’s observations were destroyed in old observatory at Uraniborg, a fire in in 1728. near Copenhagen. From there, he moved to Paris, where he Key work worked at the Royal Observatory 1677 On the Motion of Light

60 ONE SPECIES NEVER SPRINGS FROM THE SEED OF ANOTHER JOHN RAY (1627–1705) IN CONTEXT Plants make seeds that Seeds nearly always grow grow into new plants. into plants similar to the BRANCH Biology parent plant. BEFORE One species never A plant seed does not 4th century BCE The Greeks springs from the seed grow into an adult of use the terms “genus” and a different species from “species” to describe groups of another. of similar things. its parent. 1583 Italian botanist Andrea T he modern concept of a approach persisting from ancient Cesalpino classifies plants plant or animal species Greece. The Greek philosophers based on seeds and fruits. is based on reproduction. Plato, Aristotle, and Theophrastus A species includes all individuals had discussed classification and 1623 Swiss botanist Caspar that can actually or potentially used terms such as “genus” and Bauhin classifies more than breed together to produce offspring, “species” to describe groups and 6,000 plants in his Illustrated which in turn can do the same. This subgroups of all manner of things, Exposition of Plants. concept, first introduced by English living or inanimate. In doing so, natural historian John Ray in 1686, they had invoked vague qualities AFTER still underpins taxonomy—the such as “essence” and “soul.” So 1690 English philosopher John science of classification, in which members belonged to a species Locke argues that species are genetics now plays a major role. because they shared the same artificial constructs. “essence,” rather than sharing the Metaphysical approach same appearance or the ability to 1735 Carl Linnaeus publishes During this period, the term breed with one another. Systema Naturae, the first of “species” was in common usage, his many works classifying but intricately connected with By the 17th century, myriad plants and animals. religion and metaphysics—an classifications existed. Many were organized in alphabetical order, or 1859 Charles Darwin proposes the evolution of species by natural selection in On the Origin of Species.

SCIENTIFIC REVOLUTION 61 See also: Jan Swammerdam 53 ■ Carl Linnaeus 74–75 ■ Christian Sprengel 104 ■ Charles Darwin 142–49 ■ Michael Syvanen 318–19 Nothing is invented and “petal” and “pollen” into general Wheat is a monocotyledon (a plant perfected at the same time. usage and decided that floral type whose seed contains a single leaf) as should be an important feature for defined by Ray. Around 30 species of John Ray classification, as should seed type. this major food crop have evolved from He also introduced the distinction 10,000 years of cultivation, and all of by groups derived from folklore, between monocotyledons (plants them belong to the genus Triticum. such as grouping plants according with a single seed leaf) and to which illnesses they could treat. dicotyledons (plants with two seed springs from the seed of another In 1666, Ray returned from a three- leaves). However, he recommended nor vice versa.” Ray established year European tour with a large a limit to the number of features the basis of a true-breeding group collection of plants and animals used for classification, to prevent by which a species is still defined that he and his colleague Francis species numbers multiplying to today. In so doing, he made botany Willughby intended to classify unworkable proportions. His major and zoology scientific pursuits. along more scientific lines. work, Historia Plantarum (Treatise Devoutly religious, Ray saw his on Plants), published in three work as a means of displaying Practical nature volumes in 1686, 1688, and 1704, the wonders of God. ■ Ray introduced a novel practical, contains more than 18,000 entries. observational approach. He examined all parts of the plants, For Ray, reproduction was the from roots to stem tips and key to defining a species. His own flowers. He encouraged the terms definition came from his experience gathering specimens, sowing seeds, and observing their germination: “no surer criterion for determining [plant] species has occurred to me than the distinguishing features that perpetuate themselves in propagation from seed…Animals likewise that differ specifically preserve their distinct species permanently; one species never John Ray Born in 1627 in Black Notley, He married Margaret Oakley Essex, England, John Ray was the in 1673 and, after leaving son of the village blacksmith and Willughby’s household, lived the local herbalist. At 16, he went quietly in Black Notley to the to Cambridge University, where age of 77. He spent his later he studied widely and lectured on years studying specimens in topics from Greek to mathematics, order to assemble ever-more before joining the priesthood ambitious plant and animal in 1660. To recuperate from an catalogues. He wrote more illness in 1650, he had taken to than 20 works on plants and nature walks and developed an animals and their taxonomy, interest in botany. form, and function, and on theology and his travels. Accompanied by his wealthy student and supporter Francis Key work Willughby, Ray toured Britain and Europe in the 1660s, studying 1686–1704 Historia Plantarum and collecting plants and animals.

GRAVITY AFFECTS EVERYTHING IN THE UNIVERSE ISAAC NEWTON (1642–1727)



64 ISAAC NEWTON Why does the apple always fall downward, never sideways or upward? IN CONTEXT There must be an attraction toward the BRANCH center of Earth. Physics Could this attraction extend beyond the BEFORE apple, and reach as far as the Moon? If so, 1543 Nicolaus Copernicus argues that the planets orbit it would affect the orbit of the Moon. the Sun, not Earth. Could it actually cause the orbit of the 1609 Johannes Kepler argues Moon? In that case… that the planets move freely in elliptical orbits around the Sun. Gravity affects everything in the universe. 1610 Galileo’s astronomical observations support Copernicus’s views. AFTER 1846 Johann Galle discovers Neptune after French mathematician Urbain Le Verrier uses Newton’s laws to calculate where it should be. 1859 Le Verrier reports that Mercury’s orbit is not explained by Newtonian mechanics. 1915 With his general theory of relativity, Albert Einstein explains gravity in terms of the curvature of space-time. A t the time Isaac Newton “fixed” stars. This model was apple toward the center of was born, the heliocentric superseded when Johannes Kepler Earth was the same force that model of the universe, in published his laws of planetary kept the planets in their orbits which Earth and the other planets motion in 1609. Kepler dispensed around the Sun, and demonstrated orbit the Sun, was the accepted with Copernicus’s crystalline mathematically how this force explanation for the observed spheres, and showed that the orbits changed with distance. The movements of the Sun, Moon, and of the planets were ellipses, with mathematics he used involved planets. This model was not new, the Sun at one focus of each ellipse. Newton’s three Laws of Motion and but had returned to prominence He also described how the speed of his Law of Universal Gravitation. when Nicolaus Copernicus a planet changes as it moves. published his ideas at the end of Changing ideas his life in 1543. In Copernicus’s What all these models of the For centuries, scientific thinking model, the Moon and each of universe lacked was an explanation had been dominated by the ideas the planets revolved in its own of why the planets moved in the of Aristotle, who reached his crystalline sphere around the Sun, way they did. This is where conclusions without carrying out with an outer sphere holding the Newton came in. He realized experiments to test them. Aristotle that the force that pulled an

SCIENTIFIC REVOLUTION 65 See also: Nicolaus Copernicus 34–39 ■ Johannes Kepler 40–41 ■ Galileo Galilei 42–43 ■ Christiaan Huygens 50–51 ■ William Herschel 86–87 ■ Albert Einstein 214–21 taught that moving objects only a force acts on it, and a moving pushing the car forward balance kept moving as long as they were object continues to move with the forces trying to slow it down, being pushed, and that heavy constant velocity unless a force there is no net force and the car objects fell faster than lighter ones. acts on it. Here, velocity means will maintain a constant velocity. Aristotle explained that heavy both the direction of a moving objects fell to Earth because they object and its speed. So an object Newton’s Second Law states were moving toward their natural will only change its speed or that the acceleration (a change place. He also said that celestial change direction if a force acts on of velocity) of a body depends on bodies, being perfect, must all it. The force that is important is the the size of the force acting on it, move in circles at constant speeds. net force. A moving car has many and is often written down as forces on it, including friction and F = ma, where F is force, m is mass, Galileo Galilei came up with air resistance, and also the engine and a is acceleration. This shows a different set of ideas, arrived at driving the wheels. If the forces that the greater the force on a body, through experiment. He observed the greater the acceleration. ❯❯ balls running down ramps and Rocket demonstrated that objects all fall pushed at the same rate if air resistance is minimal. He also concluded that up moving objects continue to move unless a force, such as friction, Exhaust flow acts to slow them down. Galileo’s pushed down Principle of Inertia was to become part of Newton’s First Rocket engines Law of Motion. Since friction and are an example of air resistance act on all moving Newton’s Third Law objects that we encounter in daily in action. The rocket life, the concept of friction is not produces a jet that is immediately obvious. It was only forced downward. by careful experimentation that The jet exerts an equal Galileo could show that the force and opposite force that keeping something moving at a pushes the rocket up. steady speed was only needed to counteract friction. Laws of motion Newton experimented in many areas of interest, but no records of his experiments on motion survive. His three laws, however, have been verified in many experiments, holding true for speeds well below the speed of light. Newton stated his first law as: “Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon.” In other words, a stationary object will only start to move if

66 ISAAC NEWTON It also shows that the I have not been able to body such as Earth. acceleration depends on the mass discover the cause of these Newton, seeing an apple fall from a of a body. properties of gravity from tree, reasoned that Earth must be For a given force, a body with a attracting the apple and, since the small mass will accelerate faster phenomena, and I frame apple always fell perpendicular to than one with a larger mass. no hypotheses. the ground, its direction of fall was Isaac Newton directed to the center of Earth. So The Third Law is stated as the attractive force between Earth “For every action there is an equal Cambridge. At that time, several and the apple must act as if it and opposite reaction.” It means people had suggested that there originated in the center of Earth. that all forces exist in pairs: if was an attractive force from the These ideas opened the way to one object exerts a force on a Sun, and that the size of this force treating the Sun and planets as second object, then the second was inversely proportional to the small points with large masses, object simultaneously exerts a force square of the distance. In other which made calculations much on the first object, and both forces words, if the distance between easier by measuring from their are equal and opposite. In spite of the Sun and another body is centers. Newton saw no reason the term “action,” movement is not doubled, the force between them to think that the force that made required for this to be true. This is only one quarter of the original an apple fall was any different from is linked to Newton’s ideas about force. However, it was not thought the forces that kept the planets in gravity, since one example of his that this rule could be applied their orbits. Gravity, then, was a Third Law is the gravitational close to the surface of a large universal force. attraction between bodies. Not only is Earth pulling on the Moon, If Newton’s theory of gravity is but the Moon is pulling on Earth applied to falling bodies, M1 is the with the same force. mass of Earth and M2 is the mass of the falling object. So the greater Universal attraction the mass of an object, the greater Newton started thinking about the force pulling it downward. gravity in the late 1660s, when he However, Newton’s Second Law retired to the village of Woolsthorpe tells us that a larger mass does not for a couple of years to avoid accelerate as quickly as a smaller the plague that was ravaging one if the force is the same. So the greater force is needed to Newton’s Law of Gravity produces the equation below, accelerate the greater mass, and all which shows how the force produced depends on the mass of objects fall at the same speed, as the two objects and the square of the distance between them. long as there are no other forces such as air resistance to complicate The gravitational The masses of the matters. With no air resistance, a hammer and a feather will fall at constant (G). GM M two bodies (M). the same speed—a fact finally demonstrated in 1971 by astronaut F= 12 Dave Scott, who carried out the experiment on the surface of the rThe force of 2 The distance Moon during the Apollo 15 mission. attraction between between them (r). Newton described a thought experiment to explain orbits in two masses (F). an early draft of the Philosophiae Naturalis Principia Mathematica. He imagined a cannon on a very high mountain, firing cannon balls horizontally at higher and higher speeds. The higher the speed at

SCIENTIFIC REVOLUTION 67 If a cannon ball is fired with insufficient speed, gravity will pull it to Earth (A and B). If fired with sufficient speed, it will orbit Earth (C). To myself I am only a child C playing on the beach, while A vast oceans of truth lie undiscovered before me. Isaac Newton B but had lost his notes. Halley encouraged Newton to redo the Newton’s thought experiment described a cannon work, and as a result, Newton fired horizontally from a high mountain. The greater the produced On the Motion of Bodies force firing the cannon ball, the farther it travels before in an Orbit, a short manuscript sent falling to the ground. If it is fired hard enough, it will to the Royal Society in 1684. In this travel right around the planet back to the mountain. paper, Newton showed that the elliptical motion of the planets that which a ball is fired, the farther whizzing off into space in a straight Kepler described would result from away it will land. If it is launched line. In this case, Earth’s gravity a force pulling everything toward sufficiently fast, it will not land at only changes the direction of the the Sun, where that force was all, but continue around Earth until satellite’s velocity, not its speed. inversely proportional to the it arrives back at the top of the distance between the bodies. mountain. In the same way, a Publishing the ideas Newton expanded on this work, satellite launched into orbit at In 1684, Robert Hooke boasted and included other work on forces the correct speed will continue to his friends Edmond Halley and motion, in the Principia to circle Earth. The satellite is and Christopher Wren that he Mathematica, which was published continually being accelerated had discovered the laws of in three volumes and contained, by Earth’s gravity. It moves at a planetary motion. Halley was a among other things, the Law of constant speed, but its direction friend of Newton, and asked him Universal Gravitation and Newton’s is continually changing, making about this. Newton said that he three Laws of Motion. The volumes it circle the planet rather than had already solved the problem, were written in Latin, and it was not until 1729 that the first English translation was published, based on Newton’s third edition of the Principia Mathematica. Hooke and Newton had already fallen out over Hooke’s criticisms of Newton’s theory of light. Following Newton’s publication, however, much of Hooke’s work on planetary motion was obscured. However, Hooke had not been the only one to suggest such a law, and he had not demonstrated that it ❯❯

68 ISAAC NEWTON Newton’s laws provided the tools to calculate the orbits of heavenly bodies such as Halley’s comet, shown here on the Bayeux Tapestry after its appearance in 1066. worked. Newton had shown that so the mathematics was correct. Using the equations his Law of Universal Gravitation However, Newton’s laws described Edmond Halley used Newton’s and laws of motion could be used so many phenomena that they soon equations to calculate the orbit mathematically to describe the came to be widely accepted, and of a comet seen in 1682, and orbits of planets and comets, today the internationally used unit showed that it was the same comet and that these descriptions of force is named after him. as that observed in 1531 and 1607. matched observations. The comet is now called Halley’s Why should that apple always comet. Halley successfully Sceptical reception descend perpendicularly to the predicted that it would return in Newton’s ideas on gravity were ground, thought he to himself... 1758, which was 16 years after his not welcomed everywhere. The death. This was the first time that “action at a distance” of Newton’s William Stukeley comets had been shown to orbit the force of gravity, with no way Sun. Halley’s comet passes close to of explaining how or why it Earth every 75–76 years, and was happened, was seen as an the same comet as that seen in “occult” idea. Newton himself 1066 before the Battle of Hastings refused to speculate on the nature in southern England. of gravity. For him, it was enough that he had shown that the idea The equations were also used of an inverse-square attraction successfully to discover a new could explain planetary motions, planet. Uranus is the seventh planet from the Sun, and was identified as a planet by William Herschel in 1781. Herschel found the planet by chance while making careful observations of the night sky. Further observations of Uranus allowed astronomers to calculate its orbit and to produce tables predicting where it could be observed at future dates. These predictions were not always correct, however, leading to the idea that there must be another planet beyond Uranus whose gravity was affecting the orbit of Uranus. By 1845, astronomers had calculated where this eighth planet should be in the sky, and Neptune was discovered in 1846. Problems with the theory For a planet with an elliptical orbit, the point of closest approach to the Sun is called the perihelion. If there were only one planet orbiting the

SCIENTIFIC REVOLUTION 69 Sun, the perihelion of its orbit Nature and nature’s laws lay Isaac Newton would stay in the same place. hid in night; God said “Let However all the planets in our solar Newton be” and all was light. Born on Christmas Day in system affect each other, so the 1642, Isaac Newton attended perihelia precess (rotate) around Alexander Pope school in Grantham, before the Sun. Like all the other planets, studying at Trinity College, Mercury’s perihelion precesses, involved is small compared to Cambridge, where he but the precession cannot be the speed of light. So for the graduated in 1665. During completely accounted for using calculations involved in designing his life, Newton was variously Newton’s equations. This was airplanes or cars, or figuring out Professor of Mathematics at recognized as a problem in 1859. how strong the components of Cambridge, Master of the More than 50 years later, Einstein’s a skyscraper need to be, the Royal Mint, Member of Theory of General Relativity equations of classical mechanics Parliament for Cambridge described gravity as an effect of are both accurate enough and University, and President of the curvature of space-time, and much simpler to use. Newtonian the Royal Society. Besides calculations based on this theory mechanics, while it may not strictly his dispute with Hooke, do account for the observed be correct, is still widely used. ■ Newton became involved precession of Mercury’s orbit, in a feud with German as well as other observations not The precession (change in the mathematician Gottfried linked to Newton’s laws. rotational axis) of the orbit of Mercury Leibnitz over priority in the was the first phenomenon that could development of calculus. Newton’s laws today not be explained by Newton’s laws. Newton’s laws form the basis of In addition to his what is referred to as “classical scientific work, Newton mechanics”—a set of equations spent much time in alchemical used to calculate the effects of investigations and Biblical forces and motion. Although these interpretation. A devout but laws have been superseded by unorthodox Christian, he equations based on Einstein’s successfully managed to theories of relativity, the two sets avoid being ordained as a of laws agree as long as any motion priest, which was normally a requirement for some of the offices he held. Key works 1684 On the Motion of Bodies in an Orbit 1687 Philosophiae Naturalis Principia Mathematica 1704 Opticks

EXPAND HORIZO 1700–1800

ING NS

72 INTRODUCTION English clergyman George Hadley explains Georges-Louis Leclerc, Henry Cavendish Stephen Hales the behavior of the trade later the Comte de makes hydrogen, or winds in a short paper Buffon, publishes inflammable air, by publishes Vegetable the first volume of reacting zinc with acid. Statick, demonstrating that remains unknown Histoire Naturelle. for decades. root pressure. 1727 1735 1749 1766 1735 1738 1754 1770 Swedish botanist Carl Daniel Bernoulli publishes Joseph Black’s American diplomat Linnaeus publishes Hydrodynamica, which doctoral thesis on and scientist Benjamin Systema Naturae, the lays the foundation for beginning of his the kinetic theory carbonates is a Franklin publishes classification of of gases. pioneering work in a chart of the flora and fauna. Gulf Stream. quantitative chemistry. A t the end of the 17th Daniel Bernoulli, the brightest in oxygen and several other new century, Isaac Newton set a family of Swiss mathematicians, gases. Dutchman Jan Ingenhousz down his laws of motion formulated the Bernoulli principle— picked up where Priestley left off and gravity, making science more that the pressure of a fluid falls and showed how green plants give precise and mathematical than it when it is moving. This allowed off oxygen in sunlight and carbon had ever been before. Scientists him to measure blood pressure. dioxide in the dark. Meanwhile, in in various fields identified the It is also the principle that allows France, Antoine Lavoisier showed underlying principles governing aircraft to fly. that many elements, including the universe, and the various carbon, sulfur, and phosphorus, branches of scientific enquiry In 1754, Scottish chemist burn by combining with oxygen became increasingly specialized. Joseph Black, who would later to form what we now call oxides, formulate the theory of latent heat, thus debunking the theory that Fluid dynamics produced a remarkable doctoral combustible materials contain a In the 1720s, Stephen Hales, thesis about the decomposition substance called phlogiston that an English curate, performed a of calcium carbonate and the make them burn. (Unfortunately, series of experiments with plants, generation of “fixed air,” or carbon French revolutionaries would send discovering root pressure—by dioxide. This sparked a chain Lavoisier to the guillotine.) which sap rises through plants— reaction of chemical research and and inventing the pneumatic discovery. In England, reclusive In 1793, French chemist Joseph trough, a laboratory apparatus genius Henry Cavendish isolated Proust discovered that chemical for collecting gases, which was hydrogen gas and demonstrated elements nearly always combine to prove useful for later work that water is made of two parts of in definite proportions. This was a identifying the components of air. hydrogen to one of oxygen. Dissident vital step toward figuring out the minister Joseph Priestley isolated formulae of simple compounds.

EXPANDING HORIZONS 73 Joseph Priestley makes Nevil Maskelyne James Hutton publishes Thomas Malthus oxygen by heating calculates the his theory concerning produces his first density of Earth essay on human mercuric oxide, using by measuring the the age of Earth. population, which sunlight and a magnifying gravitational later influences attraction of Charles Darwin and glass; he calls it Alfred Russel Wallace. dephlogisticated air. a mountain. 1774 1774 1788 1798 1799 1774 1779 1793 Antoine Lavoisier, after Jan Ingenhousz Christian Sprengel Alessandro Volta learning the technique discovers that green describes plant invents the from Priestley, makes the plants in sunlight give same gas, and goes on to sexuality in his book electric battery. off oxygen; this is on pollination. call it oxygène. photosynthesis. Earth sciences geology after inheriting farmland and wrote An Essay on the At the other end of the scale, in Scotland, and realized that Principle of Population, predicting understanding of Earth processes Earth was a great deal older than catastrophe as the population was making great advances. In the anyone had previously thought. grows. Malthus’s pessimism has Americas, Benjamin Franklin, in proved unfounded (so far), but his addition to performing a dangerous Understanding life idea that a population will grow to experiment to prove that lightning As scientists learned of Earth’s outstrip resources if left unchecked is a form of electricity, demonstrated extreme age, new ideas about how was later to have a profound the existence of large-scale ocean life originated and evolved began influence on Charles Darwin. currents with his investigations to emerge. Georges-Louis Leclerc, of the Gulf Stream. George Hadley, Comte de Buffon, a larger-than-life At the end of the century, Italian English lawyer and amateur French author, naturalist, and physicist Alessandro Volta opened meteorologist, published a short mathematician, took the first up a new world by inventing the paper explaining the action of steps toward a theory of evolution. electric battery, which was to the trade winds in relation to the German theologian Christian accelerate advances in the decades rotation of Earth, while Nevil Sprengel spent much of his life that followed. Such had been the Maskelyne seized on an idea from studying the interaction of plants progress through the 18th century Newton and camped out for several and insects, and noted that that English philosopher William months in terrible weather to bisexual flowers produce male and Whewell proposed the creation of a measure the gravitational attraction female flowers at different times, new profession distinct from that of of a Scottish mountain. In doing so, so they cannot fertilize themselves. philosopher: “We need very much he figured out the density of Earth. English parson Thomas Malthus a name to describe a cultivator of James Hutton became interested in turned his attention to demography science in general. I should incline to call him a Scientist.” ■

74 NATURE DOES NOT PROCEED BY LEAPS AND BOUNDS CARL LINNAEUS (1707–1778) IN CONTEXT T he classification of the appeared. By the 17th century, natural world into a clear scientists were striving to set out BRANCH hierarchy of groups of a more coherent and consistent Biology named and described organisms is system. In 1686, English botanist a foundation stone of the biological John Ray introduced the concept BEFORE sciences. These groupings help of the biological species, defined c.320 BCE Aristotle groups to make sense of life’s diversity, by the ability of plants or animals similar organisms on a scale allowing scientists to compare to reproduce with one another, of increasing complexity. and identify millions of individual and this remains the most widely organisms. Modern taxonomy— accepted definition today. 1686 John Ray defines a the science of identifying, naming, biological species in his and classifying organisms—began KINGDOM Historia Plantarum. with the Swedish naturalist, Carl Animalia Linnaeus. He was the first to devise AFTER a systematic hierarchy, based on PHYLUM 1817 French zoologist Georges his wide-ranging and detailed Chordata Cuvier extends the Linnaean study of physical characteristics hierarchy in his study of fossils of plants and animals. He also CLASS as well as living animals. pioneered a way of naming different Mammalia organisms that is still in use today. 1859 Charles Darwin’s On the ORDER Origin of Species sets out how The most influential of early Carnivora species arise and are related in classifications was that of the his theory of evolution. Greek philosopher Aristotle. In his FAMILY History of Animals, he grouped Felidae 1866 German biologist Ernst similar animals into broad genera, Haeckel pioneers the study of distinguished the species within GENUS evolving lineages, known as each group, and ranked them on a Panthera phylogenetics. scala naturae or “ladder of life” with 11 grades of increasing complexity SPECIES 1950 Willi Hennig bases a in form and purpose, from plants at Panthera new system of classification the base to humans at the apex. tigris on cladistics, which looks for evolutionary links. Over the ensuing centuries, a Linnaeus’s system groups organisms chaotic multiplicity of names and according to shared characteristics. A descriptions of plants and animals tiger belongs to the cat family Felidae, which in turn belongs to the order Carnivora, in the class Mammalia.

EXPANDING HORIZONS 75 See also: Jan Swammerdam 53 ■ John Ray 60–61 ■ Jean-Baptiste Lamarck 118 ■ Charles Darwin 142–49 In 1735, Linnaeus produced a Linnaean classification Cladistic classification classification in a 12-page booklet groups like with like. groups organisms with a that grew into a multivolume 12th edition by 1778 and developed the For Linnaeus, the common ancestor. idea of the genus into a hierarchy order of life reflects of groupings based on shared God’s creation. The order of life reflects physical characteristics. At the top evolution over time. were three kingdoms: animals, Nature does not plants, and minerals. Kingdoms proceed by leaps DNA is used to were divided into phyla, then map evolutionary classes, orders, families, genera, and bounds. and species. He also stabilized the relationships. naming of species by using a two- “natural hierarchy,” with all species part Latin name, with one name in a genus or family related by with one or more shared unique for the genus and another for a descent and divergence from a characteristics, which they have species within that genus, as in common ancestor. A century after inherited from their last common Homo sapiens—Linnaeus was the Darwin, German biologist Willi ancestor and which are not found first to define humans as animals. Hennig developed a new approach in more distant ancestors. The to classification, called cladistics. process of classification by clades God-given order To reflect their evolutionary links, continues to this day, with species For Linnaeus, classification this groups organisms into “clades” reassigned new positions as fresh, revealed that “nature does not often genetic, evidence is found. ■ proceed in leaps and bounds” but rather in its God-given order. His work was the fruit of numerous expeditions across Sweden and Europe in search of new species. His classification system paved the way for Charles Darwin, who saw the evolutionary significance of its Carl Linnaeus Born in 1707 in rural southern the world collecting plants. With Sweden, Carl Linnaeus studied this vast collection, Linnaeus medicine and botany in the expanded his Systema Naturae universities of Lund and Uppsala, through 12 editions into a and earned a degree in medicine multivolume work, more than in the Netherlands in 1735. Later 1,000 pages long, encompassing that year he published a 12-page more than 6,000 species of booklet called Systema Naturae, plants and 4,000 animals. By the which outlined a system of time he died in 1778, Linnaeus classification for living organisms. was one of the most acclaimed After further travels in Europe, scientists in Europe. Linnaeus returned to Sweden in 1738 to practice medicine before Key works being appointed professor of medicine and botany at Uppsala 1753 Species Plantarum University. His students, most 1778 Systema Naturae, famously Daniel Solander, traveled 12th edition

76 THE HEAT THAT DISAPPEARS IN THE CONVERSION OF WATER INTO VAPOR IS NOT LOST JOSEPH BLACK (1728–1799) IN CONTEXT Heat generally raises the temperature of water. BRANCH But when water boils, the temperature stops rising. Chemistry and physics Additional heat is needed to turn the liquid into vapor. BEFORE This latent heat gives steam a terrible scalding power. 1661 Robert Boyle pioneers the isolation of gases. The heat that disappears in the conversion of water into vapor is not lost. 1750s Joseph Black weighs materials before and after A professor of medicine at about the costs of running their chemical reactions—the first the University of Glasgow businesses. Why, they asked quantitative chemistry—and and later at Edinburgh, him, was it so expensive to discovers carbon dioxide. Joseph Black also gave lectures distill whisky, when all they were on chemistry. Although he was a doing was boiling the liquid AFTER notable research scientist, he rarely and condensing the vapor. 1766 Henry Cavendish published his results formally, but isolates hydrogen. instead announced them during his An idea brought to the boil lectures; his students were at the In 1761, Black investigated the 1774 Joseph Priestley isolates cutting edge of new science. effects of heat on liquids, and oxygen and other gases. discovered that if a pan of water is Some of Black’s students were heated on a stove, the temperature 1798 American-born British the sons of Scottish whisky increases steadily until it reaches physicist Benjamin Thompson distillers, who were concerned suggests that heat is produced by the movement of particles. 1845 James Joule studies the conversion of motion into heat and measures the mechanical equivalent of heat, stating that a given quantity of mechanical work generates the same amount of heat.

EXPANDING HORIZONS 77 See also: Robert Boyle 46–49 ■ Joseph Priestley 82–83 ■ Antoine Lavoisier 84 ■ John Dalton 112–13 ■ James Joule 138 212°F (100°C). Then the water Melting ice Joseph Black begins to boil, but the temperature Just as heat is needed to turn water does not change, even though heat into steam, so it is needed to turn Born in Bordeaux, France, is still going into the water. Black ice into water. The latent heat of Joseph Black studied medicine realized that the heat is needed to melting ice means that ice will cool at the universities of Glasgow turn the liquid into vapor—or, in a drink. To melt the ice requires and Edinburgh, conducting modern terms, to give the molecules heat, and this heat is extracted chemical experiments in the enough energy to escape from from the drink in which it floats, laboratory of his professor. the bonds that hold them fast in the thus cooling down the liquid. In his 1754 doctoral thesis, liquid. This heat does not change Black showed that when chalk the temperature, and seems to Black explained all this to the (calcium carbonate) is heated disappear—so Black called it latent distillers, although he was unable to become quicklime (calcium heat (from the Latin for “hidden”). to help them save money. He also oxide), it does not gain some More precisely, it is the latent explained it to a colleague called fiery principle from the fire, as heat of evaporation of water. This James Watt, who was trying to was commonly believed, but discovery was the beginning of the figure out why steam engines were loses weight. Black realized science of thermodynamics—the so inefficient. Subsequently, Watt that this loss must be a gas, study of heat, its relation to energy, came up with the idea of the since no liquid or solid was and the conversion of heat energy separate condenser, which produced, and called it “fixed into motion to do mechanical work. condensed the steam without air” because it was an air (gas) cooling the piston and cylinder. that had been fixed in the Water has an unusually high This made the steam engine a chalk. He also showed that latent heat, meaning that liquid far more efficient machine, and fixed air (which we now know water will boil for a long time before made Watt a rich man. ■ as carbon dioxide) was among it all turns into gas. This is why the gases that we exhale. steaming is such an effective way Black is shown here visiting the of cooking vegetables, why steam engineer James Watt at his workshop While professor of medicine has terrible scalding power, and in Glasgow. Watt is demonstrating one at Glasgow from 1756, Black why it is used in heating systems. of his steam-powered instruments. conducted his landmark research on heat. Although he did not publish his results, his students circulated his findings. After moving to Edinburgh in 1766, he gave up research to focus on lecturing and—as the Industrial Revolution gathered speed— advising on chemical-based innovations in Scottish industry and agriculture.

78 INFLAMMABLE AIR HENRY CAVENDISH (1731–1810) IN CONTEXT When a metal such as zinc These bubbles reacts with dilute acid, may be a new air. BRANCH it produces bubbles. Chemistry This must be an They burn rapidly BEFORE inflammable air. when ignited. 1661 Robert Boyle defines an element, laying the foundations In 1754, Joseph Black had Cavendish set out to measure the for modern chemistry. described what we now call weight of a sample of the gas, by carbon dioxide (CO2) as “fixed measuring the loss of weight of 1754 Joseph Black identifies air.” He was not only the first the zinc-acid mixture during the a gas, carbon dioxide, which scientist to identify a gas, but also reaction, and by collecting all he calls “fixed air.” demonstrated that there were the gas produced in a bladder and various kinds of “air,” or gases. weighing it—first full of the gas, AFTER then empty. Knowing the volume, 1772–75 Joseph Priestley Twelve years later, an English he could calculate its density. He and (independently) Sweden’s scientist named Henry Cavendish found that inflammable air was 11 Carl Scheele isolate oxygen, reported to the Royal Society in times less dense than ordinary air. followed by Antoine Lavoisier, London that the metals zinc, iron, who names the gas. Priestley and tin “generate inflammable air The discovery of low-density also discovers nitric oxide, by solution in acids.” He called his gas led to aeronautical balloons nitrous oxide, and hydrogen new gas “inflammable air” because that were lighter than air. In France chloride, and experiments with it burned easily, unlike ordinary in 1783, inventor Jacques Charles inhaling oxygen and making or “fixed air.” Today we call it launched the first hydrogen balloon, soda water. hydrogen (H2). This was the second less than two weeks after the gas to be identified and the first Montgolfier brothers launched 1799 Humphry Davy suggests gaseous element to be isolated. their first manned hot-air balloon. nitrous oxide could be useful as an anesthetic in surgery. 1844 Nitrous oxide is first used for anesthesia by American dentist Horace Wells.

EXPANDING HORIZONS 79 See also: Empedocles 21 ■ Robert Boyle 46–49 ■ Joseph Black 76–77 ■ Joseph Priestley 82–83 ■ Antoine Lavoisier 84 ■ Humphry Davy 114 It appears from these Cavendish’s thinking was still to Joseph Priestley, Cavendish was experiments, that this air, like handicapped by an obsolete notion so diffident about publishing the other inflammable substances, from alchemy that a firelike element results that his friend the Scottish (“phlogiston”) was released during engineer James Watt was the first cannot burn without the combustion. However, he was to announce the formula, in 1783. assistance of common air. precise in his experiments and in his reporting: “it appears that 423 Among his many contributions Henry Cavendish measures of inflammable air are to science, Cavendish went on to nearly sufficient to phlogisticate calculate the composition of air Explosive discoveries 1,000 of common air; and that the as “one part dephlogisticated Cavendish also mixed measured bulk of the air remaining after air [oxygen], mixed with four of samples of his gas with known the explosion is then very little phlogisticated [nitrogen]”—the volumes of air in bottles, and more than four-fifths of the common two gases we now know make up ignited the mixtures by taking air employed. We may conclude 99 percent of Earth’s atmosphere. ■ the tops off and applying lighted that…almost all the inflammable pieces of paper. He found that with air and about one fifth of the The first hydrogen balloon, inspired nine parts of air to one of hydrogen common air…are condensed by Cavendish, was cheered by a huge there was a slow, quiet flame; with into the dew which lines the glass.” crowd of spectators. Since hydrogen is so increasing proportions of hydrogen explosive, modern balloons use helium. the mixture exploded with Defining water increasing ferocity; but pure, 100 Although Cavendish used the term percent hydrogen did not ignite. “phlogisticate,” he managed to demonstrate that the only new material produced was water, and deduced that two volumes of inflammable air had combined with one volume of oxygen. In other words, he showed that the composition of water is H2O. Although he reported his findings Henry Cavendish One of the strangest and most did significant original research brilliant pioneers of 18th century into chemistry and electricity, chemistry and physics, Henry accurately described the nature Cavendish was born in 1731 in of heat, and measured Earth’s Nice, France. His grandfathers density—or, as people said, were both dukes, and he was “weighed the world.” He died immensely rich. After his studies in 1810. In 1874, the University at the University of Cambridge, of Cambridge named its new he lived and worked alone in his physics laboratory in his honor. house in London. A man of few words and shy of women, it was Key works said that he ordered his meals by leaving notes for his servants. 1766 Three Papers Containing Experiments on Factitious Air Cavendish attended meetings 1784 Experiments on Air of the Royal Society for about 40 (Philosophical Transactions of years, and also assisted Humphry the Royal Society of London) Davy at the Royal Institution. He

80 WINDS, AS THEY COME NEARER THE EQUATOR, BECOME MORE EASTERLY GEORGE HADLEY (1685–1768) IN CONTEXT B y 1700, it was known that at its greatest over the equator, persistent surface winds, or causes air to rise, and that rising BRANCH “trade winds,” blow from a air is replaced by winds blowing Meteorology northeasterly direction between in from higher latitudes. a latitude of 30°N and the equator BEFORE at 0°. Galileo had suggested that In 1735, English physicist 1616 Galileo Galilei points to Earth’s eastward rotation made it George Hadley published his trade winds as evidence of “get ahead” of the air in the tropics, theory on trade winds. He agreed Earth’s rotation. so the winds come from the east. that the Sun causes air to rise, but Later, English astronomer Edmond rising air near the equator would 1686 Edmond Halley proposes Halley realized that the Sun’s heat, only cause winds to flow toward it that the Sun traveling west from the north and south, not from through the sky causes air to Earth rotates the east. As the air rotates with rise and be replaced by winds toward the east Earth, air moving from 30° N from the east. toward the equator would have its Easterly 60°N own momentum toward the east. AFTER trade 30°N However, Earth’s surface moves 1793 John Dalton publishes winds 0° faster at the equator than at higher Meteorological Observations latitudes, so the surface speed and Essays, which supports Mid- 30°S becomes greater than the air’s Hadley’s theory. latitude 60°S speed and the winds appear to westerlies come from an increasingly easterly 1835 De Coriolis builds on direction as they near the equator. Hadley’s ideas, describing a Polar easterlies “compound centrifugal force” Hadley’s idea was a step on that deflects the wind. Wind patterns result from Earth’s the way to understanding wind rotation combined with circulation patterns, but contained errors. 1856 American meteorologist “cells” as hot air rises, cools, and falls The key to the deflection of wind William Ferrel identifies a in polar cells (shown in gray), Ferrel direction is in fact that the wind’s circulation cell in the mid- cells (blue), and Hadley cells (pink). angular momentum (causing it to latitudes (30–60°) where air rotate) is conserved, not its linear pulled into a low-pressure (straight-line) momentum. ■ center creates the prevailing westerly winds. See also: Galileo Galilei 42–43 ■ John Dalton 112–13 ■ Gaspard-Gustave de Coriolis 126 ■ Robert FitzRoy 150–55

EXPANDING HORIZONS 81 A STRONG CURRENT COMES OUT OF THE GULF OF FLORIDA BENJAMIN FRANKLIN (1706–1790) IN CONTEXT The warm Gulf Stream current Franklin’s chart was published in that flows eastward across 1770 in Britain, but it would be years BRANCH the North Atlantic Ocean before British captains learned to use Oceanography is one of the greatest movements the Gulf Stream to cut sailing times. of water on Earth. It is driven BEFORE east by prevailing westerly winds, could spot it by whale migrations, c.2000 BCE Polynesian and is part of a great loop that differences in temperature and color, seafarers use ocean currents to then recrosses the Atlantic to the and the speed of surface bubbles, cross between Pacific islands. Caribbean. The current had been and so they crossed over the current known since 1513, when Spanish to escape it, while the westbound 1513 Juan Ponce de Léon explorer Juan Ponce de León found British packet ships battled against is the first to describe the his ship moving back north off it all the way. strong currents of the Atlantic Florida despite winds blowing him Ocean’s Gulf Stream. south. But it was only properly With Folger’s aid, Franklin charted in 1770, by US statesman charted the current’s course as it AFTER and scientist Benjamin Franklin. flowed along the east coast of North 1847 US naval officer Matthew America from the Gulf of Mexico to Maury publishes his chart of Local advantage Newfoundland and then streamed winds and currents, compiled As deputy postmaster of the British east across the Atlantic. He also by studying ships’ logs and American colonies, Franklin was gave the Gulf Stream its name. ■ charts in naval archives. fascinated by why it took British packet ships delivering mail two 1881 Prince Albert I of weeks longer to cross the Atlantic Monaco realizes that the Gulf than American merchant ships. Stream is a gyre (loop) and Already famous for his invention of splits in two—one branch the lightning conductor, he asked flowing north toward the Nantucket whaling captain Timothy British Isles, and the other Folger why this might be. Folger south to Spain and Africa. explained that American captains knew of the west–east current. They 1942 Norwegian oceanographer Harald See also: George Hadley 80 ■ Gaspard-Gustave de Coriolis 126 ■ Sverdrup develops a theory Robert FitzRoy 150–55 of general ocean circulation.

82 DEPHLOGISTICATED AIR JOSEPH PRIESTLEY (1733–1804) IN CONTEXT F ollowing Joseph Black’s vat, the candle went out about 12 in pioneering discovery of (30 cm) above the froth, where the BRANCH “fixed air,” or carbon dioxide flame entered the layer of fixed air Chemistry (CO2), an English clergyman named floating there. The smoke drifted Joseph Priestley became interested across the top of the fixed air, BEFORE in investigating various other “airs,” making it visible and revealing 1754 Joseph Black isolates the or gases, and identified several the boundary between the two airs. first gas, carbon dioxide. more—most notably oxygen. He also noticed that the fixed air flowed over the side of the vat and 1766 Henry Cavendish While a minister in Leeds, sank to the floor, because it was prepares hydrogen. Priestley visited the brewery close denser than “ordinary” air. When to his lodgings. The layer of air Priestley experimented with 1772 Carl Scheele isolates a above the brewing vat was already dissolving fixed air in cold water, third gas, oxygen, two years known to be fixed air. He found that sloshing it from one vessel to before Priestley, but does not when he lowered a candle over the publish his findings until 1777. As Priestley discovers, Oxygen does not burn, AFTER oxygen is separate from so it cannot contain the fire 1774 In Paris, Priestley “fixed air” (carbon dioxide). demonstrates his method to element phlogiston. Antoine Lavoisier, who makes the new gas and publishes his But Lavoisier shows that other Oxygen is results in May 1775. gases and materials burn dephlogisticated air. readily in oxygen. 1779 Lavoisier gives the gas the name “oxygène.” So combustion is a process of Phlogiston combining with oxygen. does not exist. 1783 Geneva’s Schweppes Company starts making the soda water Priestley invented. 1877 Swiss chemist Raoul Pictet produces liquid oxygen, which will be used in rocket fuel, industry, and medicine.

EXPANDING HORIZONS 83 See also: Joseph Black 76–77 ■ Henry Cavendish 78–79 ■ Antoine Lavoisier 84 ■ John Dalton 112–13 ■ Humphry Davy 114 another, he found that it made a refreshing sparkling drink, which later led to the craze for soda water. Releasing oxygen The most remarkable of Joseph Priestley On August 1, 1774, Priestley first all the kinds of air I have isolated his new gas—which we produced…is, one that is Born on a farm in Yorkshire, now know as oxygen (O2)—from five or six times better than Joseph Priestley was brought mercuric oxide in a sealed glass common air, for the purpose up as a dissenting Christian, flask by heating it with sunlight and was intensely religious and a magnifying glass. He later of respiration. and political all his life. discovered that this new gas kept Joseph Priestley mice alive much longer than Priestley became ordinary air, was pleasant to not publish his results until 1777. interested in gases while breathe and more energizing than Meanwhile in Paris, Antoine living in Leeds in the early ordinary air, and supported the Lavoisier heard of Scheele’s work, 1770s, but his best work combustion of various substances was given a demonstration by was done after he moved to he burned as fuel. He also showed Priestley, and promptly made his Wiltshire as librarian to the that plants produce the gas in own oxygen. His experiments on Earl of Shelburne. His duties sunlight—a first hint of the process combustion and respiration proved were light and left him time we call photosynthesis. At the time, that combustion is a process of to conduct research. He later however, combustion was thought combining with oxygen, not fell out with the earl—his to involve the release from a fuel liberating phlogiston. In respiration, political views may have been of a mysterious material called oxygen absorbed from the air too radical—and in 1780, he phlogiston. Because this new gas reacts with glucose and releases moved to Birmingham. Here did not burn, and therefore must carbon dioxide, water, and energy. he joined the Lunar Society, contain no phlogiston, he called it He named the new gas oxygène, or an informal but influential “dephlogisticated air.” “acid-maker,” when he discovered group of freethinkers, that it reacts with some materials— engineers, and industrialists. Priestley isolated several other such as sulfur, phosphorus, and gases at about this time, but then nitrogen—to make acids. Priestley’s support for the went on a European tour, and did French Revolution made him not publish his results until late the This led many scientists to unpopular. In 1791, his house following year. Swedish chemist abandon phlogiston, but Priestley, and laboratory were burned Carl Scheele had prepared oxygen though a great experimenter, clung down, forcing him to move to two years before Priestley, but did to the old theory to explain his London and then to America. discoveries and made little further He settled in Pennsylvania, contribution to chemistry. ■ and died there in 1804. Priestley’s apparatus for his gas Key works experiments appear in his book about his discoveries. At the front, a mouse is 1767 The History and Present kept in oxygen under a jar; on the right, State of Electricity a plant releases oxygen in a tube. 1774–77 Experiments and Observations on Different Kinds of Air

84 IN NATURE, NOTHING IS CREATED, NOTHING IS LOST, EVERYTHING CHANGES ANTOINE LAVOISIER (1743–1794) IN CONTEXT French chemist Antoine combustion, demolished the theory Lavoisier brought a new of a fire element called phlogiston. BRANCH level of precision to science, For the past century, scientists had Chemistry not least by naming oxygen and thought inflammable substances quantifying its role in combustion. contained phlogiston and released BEFORE By taking careful measurements it when they burned. The theory 1667 German alchemist of mass in the chemical reactions explained why substances such as Johann Joachim Becher that occur during combustion, wood lost mass on burning, but not proposes that things are made he demonstrated the conservation why others, such as magnesium, to burn by a fire element. of mass—the principle that, in a gained mass on burning. Lavoisier’s reaction, the total mass of all the careful measurements showed that 1703 German chemist Georg substances taking part is the same oxygen was the key, in a process Stahl renames it phlogiston. as the total mass of all its products. during which nothing was added or lost, but all was transformed. ■ 1772 Swedish chemist Lavoisier heated various Carl-Wilhelm Scheele discovers substances in sealed containers I consider nature a vast “fire air” (later called oxygen) and found that the mass a metal chemical laboratory in which but does not publish his gained when it was heated was all kinds of composition and findings until 1777. exactly equal to the mass of air lost. decompositions are formed. He also found that burning stopped 1774 Joseph Priestley isolates when the “pure” part of the air Antoine Lavoisier “dephlogisticated air” (later (oxygen) had all gone. The air that called oxygen) and tells remained (mostly nitrogen) did not Lavoisier about his findings. support combustion. He realized that combustion therefore involved AFTER a combination of heat, fuel (the 1783 Lavoisier confirms his burning material), and oxygen. ideas on combustion with experiments on hydrogen, Published in 1778, Lavoisier’s oxygen, and water. results not only demonstrated the conservation of mass, but also, 1789 Lavoisier’s Elementary by identifying oxygen’s role in Treatise on Chemistry names 33 elements. See also: Joseph Black 76–77 ■ Henry Cavendish 78–79 ■ Joseph Priestley 82–83 ■ Jan Ingenhousz 85 ■ John Dalton 112–13

EXPANDING HORIZONS 85 THE MASS OF A PLANT COMES FROM THE AIR JAN INGENHOUSZ (1730–1799) IN CONTEXT I n the 1770s, Dutch scientist Jan Pondweed bubbles at night show Ingenhousz set out to discover respiration as plants convert glucose BRANCH why plants, as earlier scientists into energy, absorbing oxygen and Biology had noticed, put on weight. He went releasing carbon dioxide. to England and did his research at BEFORE Bowood House—where Joseph carbon dioxide, was at least partly 1640s Flemish chemist Jan Priestley discovered oxygen in the source of a plant’s increased Baptista van Helmont deduces 1774—and was about to find the organic matter—that is, its extra that a potted tree gains weight keys to photosynthesis: sunlight mass came from air. by absorbing water from soil. and oxygen. As we now know, plants make 1699 English naturalist John Bubbling weeds their food by photosynthesis— Woodward shows that water is Ingenhousz had read how plants in converting energy from sunlight into both taken in and given off by water produce bubbles of gas, but glucose by reacting the water and plants, so their growth needs the bubbles’ precise composition carbon dioxide that plants absorb, another source of matter. and origin were unclear. In a series and releasing oxygen as waste. As a of experiments, he saw that sunlit result, plants supply both the oxygen 1754 Swiss naturalist Charles leaves gave off more bubbles that is vital to life, and—as food for Bonnet notices that plant than leaves in the dark. He collected others—the energy. In a reverse leaves produce bubbles of air the gas produced only in sunlight, process called respiration, plants under water when illuminated. and found that it re-lit a glowing use the glucose as food and release splint—this was oxygen. The gas carbon dioxide, day and night. ■ AFTER given off by plants in the dark put out 1796 Swiss botanist Jean a flame—this was carbon dioxide. Sénébier shows that it is the green parts in plants that Ingenhousz knew that plants put release oxygen and absorb on weight with little change in the carbon dioxide. weight of the soil they grew from. In 1779, he correctly reasoned that 1882 German scientist gas exchange with the atmosphere, Théodore Engelman pinpoints especially the absorption of the gas chloroplasts as the oxygen- making parts in plant cells. See also: Joseph Black 76–77 ■ Henry Cavendish 78–79 ■ Joseph Priestley 82–83 ■ Joseph Fourier 122–23

86 DISCOVERING NEW PLANETS WILLIAM HERSCHEL (1738–1822) IN CONTEXT New telescopes allowed Better observations showed for more detailed mapping a new planet in BRANCH orbit around the Astronomy of the skies. Sun—Uranus. BEFORE Using Newton’s laws, it Uranus’s orbit was Early 1600s The lens-based was possible to calculate irregular, suggesting that refracting telescope is invented, but mirror-based where to look for the it was being pulled telescopes are not developed new planet. by the gravity of until the 1660s, by Isaac another planet. Newton and others. Neptune was discovered. 1774 French observer Charles Messier publishes his I n 1781, German scientist through the construction of astronomical survey, inspiring William Herschel identified reflecting telescopes that used Herschel to begin work on a the first new planet to be seen mirrors rather than lenses to gather survey of his own. since ancient times, although light, avoiding many of the problems Herschel himself initially thought it associated with lenses at the time. AFTER was a comet. His discovery would This was the age of the first great 1846 Unexplained changes to also lead to the discovery of another astronomical surveys, as astronomers the orbit of Uranus lead French planet as a result of predictions scoured the sky and identified a mathematician Urbain Le based on Newton’s laws. wide variety of “nonstellar” Verrier to predict the existence objects—star clusters and nebulae and position of an eighth By the late 18th century, that looked like amorphous clouds planet—Neptune. astronomical instruments had of gas or dense balls of light. advanced significantly—not least 1930 US astronomer Clyde Tombaugh discovers Pluto, which is initially recognized as a ninth planet, but now seen as the brightest member of the Kuiper Belt of small icy worlds.

EXPANDING HORIZONS 87 See also: Ole Rømer 58–59 ■ Isaac Newton 62–69 ■ Nevil Maskelyne 102–03 ■ Geoffrey Marcy 327 In the 1780s, Herschel built his green disk that he suspected might By 1845, two astronomers— “40-foot” telescope with a 47 in (1.2 m) be a comet. He returned to it a few Frenchman Urbaine Le Verrier and wide primary mirror and a 40 ft (12 m) nights later, and found that it had Briton John Couch Adams—were focal length. It remained the largest moved, confirming that it was not independently using Bouvard’s data telescope in the world for 50 years. a star. Upon looking at Herschel’s to calculate where in the sky to look discovery, Nevil Maskelyne realized for the eighth planet. Telescopes Assisted by his sister Caroline, that the new object was moving far were trained on the predicted area, Herschel systematically quartered too slowly to be a comet, and might and on September 23, 1846, the sky, recording curiosities such in fact be a planet in a distant orbit. Neptune was discovered within just as the unexpectedly large number Swedish-Russian Anders Johan one degree of where Le Verrier had of double and multiple stars. He Lexell and German Johann Elert predicted it would be. Its existence even attempted to compile a map Bode independently computed confirmed Bouvard’s theory and of the Milky Way galaxy based on the orbit for Herschel’s discovery, provided powerful evidence of the number of stars he counted confirming that it was indeed a the universality of Newton’s laws. ■ in different directions. planet, roughly twice as far away as Saturn. Bode suggested naming it On March 13, 1781, Herschel after Saturn’s mythological father, was scanning the constellation the ancient Greek sky god Uranus. Gemini when he spotted a faint Irregular orbit I looked for the Comet or In 1821, French astronomer Alexis Nebulous Star and found Bouvard published a detailed table that it is a Comet, for it describing the orbit of Uranus as it should be according to Newton’s has changed its place. laws. However, his observations of William Herschel the planet soon showed substantial discrepancies with his table’s predictions. The irregularities of its orbit suggested a gravitational pull from an eighth, more distant planet. William Herschel Born in Hanover, Germany, performed an experiment using Frederick William Herschel a prism and a thermometer to emigrated to Britain at 19 to measure the temperatures of make a career in music. His different colors of sunlight, studies of harmonics and and found that the temperature mathematics led to an interest in continued to rise in the region optics and astronomy, and he set beyond visible red light. He out to make his own telescopes. concluded that the Sun emitted an invisible form of light, which Following his discovery of he termed “calorific rays” and Uranus, Herschel discovered two which today we call infrared. new moons of Saturn and the largest two moons of Uranus. He Key works also proved that the solar system is in motion relative to the rest of 1781 Account of a Comet the galaxy. While studying the 1786 Catalogue of 1,000 New Sun in 1800, Herschel discovered Nebulae and Clusters of Stars a new form of radiation. He

88 THE DIMINUTION OF THE VELOCITY OF LIGHT JOHN MICHELL (1724–1793) IN CONTEXT Newton shows that If light is affected the gravitational by gravity, a massive BRANCH attraction of an object enough object will have Cosmology is proportional such a strong gravitational field that no light will be BEFORE to its mass. 1686 Isaac Newton formulates able to escape it. his law of universal gravitation, in which the strength of Einstein explains The velocity the gravitational attraction gravity as a distortion of light will appear between objects is of space-time, meaning proportional to their masses. that massless light is to diminish. affected by gravity. AFTER 1796 Pierre-Simon Laplace I n a 1783 letter to Henry proportion of 500 to 1, a body falling independently theorizes about Cavendish at the Royal Society, from an infinite height toward it the possibility of black holes. British polymath John Michell would have acquired at its surface set out his thoughts on the effect of a greater velocity than that of light, 1915 Albert Einstein shows gravity. The letter was rediscovered & consequently, supposing light that gravity is a warping of the in the 1970s and found to contain to be attracted by the same force… space-time continuum, which a remarkable description of black all light emitted from such a body is why massless light photons holes. Newton’s law of gravity states would be made to return towards are affected by gravity. that an object’s gravitational pull it.” In 1796, French mathematician increases with its mass. Michell Pierre-Simon Laplace came up with 1916 Karl Schwarzschild considered what might happen to a similar idea in his Exposition du proposes the event horizon, light if it is affected by gravity. He Système du Monde. beyond which no data can be wrote: “If the semidiameter of a received about a black hole. sphere of the same density with the However, the idea of a black sun were to exceed the sun in the hole would lie dormant until Albert 1974 Stephen Hawking Einstein’s 1915 paper on general predicts that quantum effects at the event horizon will emit infrared radiation.

EXPANDING HORIZONS 89 See also: Henry Cavendish 78–79 ■ Isaac Newton 62–69 ■ Albert Einstein 214–21 ■ Subrahmanyan Chandrasekhar 248 ■ Stephen Hawking 314 Black holes ain’t so black. Stephen Hawking Matter swirls around a black hole in massive stars collapse under their unusual on the approach to the a doughnut-shaped “accretion disk” own gravity, and grow as they event horizon, but if he or she before being sucked in. Heat in the assimilate ever more matter, and dropped a clock toward the black swirling disk causes the hole to emit that a giant black hole lurks at the hole, the clock would appear to energy—as narrow beams of X-rays. center of every galaxy. Black holes slow down, and approach but pull matter in, but nothing escapes, never quite reach the event horizon, relativity, which described gravity other than faint infrared radiation, gradually fading from sight. as a result of the curving of space- known as Hawking radiation after time. Einstein showed how matter Stephen Hawking, the physicist Problems with the theory still can wrap space-time around itself, who proposed it. An astronaut exist, however. In 2012, physicist making a black hole within a region falling into a black hole would Joseph Polchinski suggested that called the Schwarzschild radius, feel nothing and notice nothing effects at the quantum scale would or event horizon. Matter—and also create a “firewall” at the event light—can enter it, but cannot John Michell horizon that would burn any leave. In this picture, the speed of astronaut falling through it to a light is unchanged. Rather, it is the John Michell was a true crisp. In 2014, Hawking changed space the light travels through that polymath. He became professor his mind and concluded that black changes, but Michell’s intuition of geology at the University of holes cannot exist after all. ■ now had a mechanism by which Cambridge in 1760, but also the velocity of light would at least taught arithmetic, geometry, “weighing the world”—a appear to diminish. theology, philosophy, Hebrew, delicate torsion balance—but and Greek. In 1767, he retired died in 1793 before he could use From theory to reality to become a clergyman, and it. He left it to his friend Henry Einstein himself doubted whether focused on his science. Cavendish, who performed black holes existed in reality. It was the experiment in 1798, and not until the 1960s that they began Michell speculated on the obtained a value close to the to acquire general acceptance as properties of stars, investigated currently accepted figure. indirect evidence of their existence earthquakes and magnetism, Ever since, this has somewhat grew. Today, most cosmologists and invented a new method for unfairly been known as “the think that black holes form when measuring the density of Earth. Cavendish experiment.” He built the apparatus for Key work 1767 An Inquiry into the Probable Parallax and Magnitude of the Fixed Stars

SETTING THE ELECTRIC FLUID IN MOTION ALESSANDRO VOLTA (1745–1827)



92 ALESSANDRO VOLTA F or centuries, philosophers A dead frog’s legs twitch had wondered at the when connected to two IN CONTEXT terrifying power of different pieces of metal. lightning, and also at the way in BRANCH which sparks can be drawn from When the two metals Physics solids such as amber when rubbed are touched to the tongue, with a silk cloth. The Greek word BEFORE for amber was “electron,” and the it produces a curious 1754 Benjamin Franklin sparking phenomenon became sensation… proves that lightning is natural known as static electricity. electricity with his famous This electrical force kite experiment. In an experiment of 1754, must come from the two Benjamin Franklin flew a kite different metals attached 1767 Joseph Priestley into a thunderstorm and showed publishes a comprehensive that these two phenomena were to the frog’s leg. account of static electricity. closely related. When he saw sparks flying from a brass key tied The force can be 1780 Luigi Galvani conducts to the kite’s line, he proved that multiplied by connecting his frog’s legs experiments the clouds were electrified, and with “animal electricity.” that lightning is also a form of a series of these metals electricity. Franklin’s work inspired in a column. AFTER Joseph Priestley to publish a 1800 English chemists William comprehensive work on The History Volta’s breakthrough Nicholson and Anthony Carlisle and Present State of Electricity in Galvani’s younger colleague use a Voltaic pile to split water 1767. But it was the Italian Luigi Alessandro Volta, a professor of into its two elements, oxygen Galvani, a lecturer in anatomy at natural philosophy, was intrigued and hydrogen. the University of Bologna, who, in by Galvani’s observations and was 1780, took the first major steps initially convinced by his theory. 1807 Humphry Davy isolates toward understanding electricity the elements potassium and when he noticed a frog’s leg twitch. Volta himself had a notable sodium using electricity. background in electricity Galvani was investigating a experiments. In 1775, he had 1820 Hans Christian Ørsted theory that animals are driven by invented the “electrophorus,” reveals the link between “animal electricity,” whatever that a device that provided an magnetism and electricity. was, and was dissecting frogs to instant source of electricity for an look for evidence of this. He noticed experiment (the modern equivalent that if there was a machine nearby is a capacitor). It consisted of a generating static electricity, a frog’s leg lying on the bench suddenly twitched, even though the frog was long dead. The same thing happened when a frog’s leg was hung on a brass hook that came into contact with an iron fence. Galvani believed this evidence supported his belief that electricity was coming from the frog itself. Luigi Galvani is shown here conducting his famous frog’s legs experiment. He believed that animals were driven by an electrical force, which he called “animal electricity.”

EXPANDING HORIZONS 93 See also: Henry Cavendish 78–79 ■ Benjamin Franklin 81 ■ Joseph Priestley 82–83 ■ Humphry Davy 114 ■ Hans Christian Ørsted 120 ■ Michael Faraday 121 resin disk rubbed with cat fur zinc, and so on, until he had a were connected by a piece of wire, to give it a static electric charge. column, or stack. In other words, and enough to give him a mild Each time a metal disk was placed he created a pile, or “battery.” The electric shock. over the resin, the charge was point of the salty wet cardboard transferred, electrifying the was to carry the electricity without The news spreads metal disk. letting the metals on either side of Volta made his discovery in it come into contact with each other. 1799, and news spread rapidly. Volta stated that Galvani’s He demonstrated the effect to animal electricity was “among The result was, literally, Napoleon Bonaparte in 1801, but the demonstrated truths.” But he electrifying. Volta’s crude battery more importantly, in March 1800, soon began to have his doubts. probably produced only a few volts he had reported his results in a He came to the conclusion that (the electrical unit named after long letter to Sir Joseph Banks, the electricity causing the frog’s him), but that was enough to make president of the Royal Society in ❯❯ legs to twitch on the hook came a tiny spark when the two ends from the touching of the two different metals (the brass and the Copper This diagram of a voltaic iron). He published his ideas in disk pile shows the copper and 1792 and 1793, and began zinc disks separated by investigating the phenomenon. cardboard soaked in salt water. Volta’s original piles Volta found that a single contained an additional junction of two different metals zinc disk at the bottom, did not produce much electricity, and an additional copper although there was enough for him disk at the top. These to feel a curious sensation with were later shown to be his tongue. But then he had the unnecessary to produce brilliant idea of multiplying the the electrical current. effect by making a series of such junctions connected by salt water. Zinc disk He took a small disk of copper, then placed a disk of zinc on top, then a piece of cardboard soaked in salt water, then another disk of copper, zinc, salty wet cardboard, copper, Cardboard disk Each metal has a certain Individual power, which is different from element metal to metal, of setting the electric fluid in motion. Alessandro Volta

94 ALESSANDRO VOLTA Britain. The letter was titled plate of silver followed immediately pieces (not more) shocks which “On the electricity excited by by another of zinc…I continue affect the whole finger with the mere Contact of conducting to form…a column as high as considerable pain.” He then Substances of different Kinds,” and possible without any danger of describes a more elaborate in it Volta describes his apparatus: its falling.” apparatus, consisting of a series “I place then horizontally, on a of cups or drinking glasses, each table or any other stand, one of the Without a buzzer or a containing salt water, arranged metallic pieces, for example one of semiconductor to detect voltage, in a line or a circle. Each pair is silver, and over the first I adapt one Volta used his body as a detector, connected by a piece of metal that of zinc; on the second I place one of and did not seem to mind getting dips into the liquid in each cup. the moistened discs, then another electric shocks: “I receive from a One end of this metal is silver, the column formed of twenty pairs of other zinc, and these metals may be soldered together or connected by a wire of any metal, provided that only the silver dips into the liquid in one cup, and only the zinc into the next. He explains that this is in some ways more convenient than the solid pile, albeit more cumbersome. Volta describes in detail the various unpleasant sensations that result from putting one hand in the bowl at one end of the chain and touching a wire attached to the other end to the forehead, eyelid, or tip of the nose: “I feel nothing for some moments; afterward, however, there begins at the part applied to the end of the wire, another sensation, which is a sharp pain (without shock), limited precisely to the point of contact, a quivering, not only continued, but which always goes on increasing to such a degree, that in a little time it becomes insupportable, and does not cease till the circle is interrupted.” Battery mania That his letter reached Banks at all is surprising, since the Napoleonic wars were in progress, Volta demonstrated his electric pile to Napoleon Bonaparte at the French National Institute in Paris in 1801. Napoleon was sufficiently impressed to make Volta a count the same year.

EXPANDING HORIZONS 95 trucks and aircraft. Without batteries, many of our everyday devices would not work. The language of experiment is Reclassifying metals Alessandro Volta more authoritative than any In addition to kick-starting the reasoning: facts can destroy study of current electricity, and Born in 1745 in Como, northern our ratiocination [logical thereby not only creating a new Italy, Alessandro Giuseppe argument]—not vice versa. branch of physics but rapidly Antonio Anastasio Volta was Alessandro Volta advancing the development of brought up in an aristocratic, modern technology, Volta’s pile religious family who hoped but Banks immediately spread led to a whole new chemical that he would become a priest. the word to anyone who might be classification of metals, for he tried Instead he became interested interested. Within weeks, people a variety of pairs of metals in his in static electricity, and, in all over Britain were making pile, and found that some worked 1775, he made an improved electric batteries and investigating much better than others. Silver device for generating it, called the properties of current electricity. with zinc made an excellent the “electrophorus.” He Before 1800, scientists had had to combination, as did copper with discovered methane in the work with static electricity, which tin, but if he tried silver and silver, atmosphere at Lake Maggiore is difficult and unrewarding. Volta’s or tin and tin, he got no electricity in 1776, and investigated its invention allowed them to find out at all; the metals had to be combustion by the novel how a range of materials—liquids, different. He showed that metals method of igniting it with solids, and gases—react to a live could be arranged in a sequence an electrical spark inside electrical current. such that each became positive a sealed glass vessel. when placed in contact with the Among the first to work with next one below it in the series. This In 1779, Volta was Volta’s discovery were William electrochemical series has been appointed professor of Nicholson, Anthony Carlisle, and invaluable to chemists ever since. physics at the University of William Cruickshank, who, in May Pavia, a post he held for 40 1800, made their own “pile of Who was right? years. Toward the end of his thirty-six half crowns with the An ironic aspect of this story is life, he pioneered the remotely correspondent pieces of zinc and that Volta started investigating the operated pistol, whereby pasteboard” and passed the current touching of different metals only an electric current traveled through platinum wires into a tube because he doubted Galvani’s 30 miles (50 km) from Como filled with water. The bubbles of hypothesis. Yet Galvani was not to Milan and fired a pistol. gas that appeared were identified entirely wrong—our nerves do This was the forerunner of as two parts of hydrogen and one indeed work by sending electrical the telegraph, which uses part of oxygen. Henry Cavendish impulses around the body—while electricity to communicate. had shown that the formula of Volta himself did not get his theory The unit of electrical potential, water is H2O, but this was the first entirely right. He believed that the volt, is named after him. time anyone had split water into its the electricity arose from just the separate elements. touching together of two different Key work metals, whereas Humphry Davy Volta’s pile was the ancestor later showed that something could 1769 On the Attractive Force of all modern batteries, used in not come from nothing. When of Electrical Fire everything from hearing aids to electricity is being generated, something else must be consumed. Davy suggested that there was a chemical reaction going on, and this led him to further important discoveries about electricity. ■

NO VESTIGE OF A BEGINNING AND NO PROSPECT OF AN END JAMES HUTTON (1726–1797)



98 JAMES HUTTON F or millennia, human All the years from the cultures have pondered creation of the world amount IN CONTEXT the age of Earth. Before the advent of modern science, to a total of 5,698 years. BRANCH estimates were based on beliefs Theophilus of Antioch Geology rather than evidence. It was not BEFORE until the 17th century that a 10th century Al-Biruni uses growing understanding of Earth’s fossil evidence to argue that geology provided the means to land must once have been determine the planet’s age. under the sea. 1687 Isaac Newton argues Biblical estimates A scientific approach that Earth’s age can be In the Judaeo-Christian world, ideas During the 10th century CE, calculated scientifically. about Earth’s age were based on scholars in Persia began to 1779 The Comte de Buffon’s descriptions in the Old Testament. consider the question of Earth’s experiments suggest an age However, since these texts only age more empirically. Al-Biruni, of 74,832 years for Earth. presented the creation story in brief a pioneer of experimental science, AFTER outline, they were subject to much reasoned that if marine fossils were 1860 John Phillips calculates interpretation, especially over the found on dry land, then that land Earth’s age at 96 million years. complex genealogical chronologies must once have been under the 1862 Lord Kelvin calculates that followed the appearance of sea. Earth, he concluded, must be Earth’s cooling to produce an Adam and Eve. evolving over long periods of time. age of 20–400 million years, Another Persian scholar, Avicenna, later settling on 20–40 million. Best known of these Biblical suggested that layers of rock had 1905 Ernest Rutherford uses calculations is that by James been laid down one upon another. radiation to date a mineral. Ussher, the protestant Primate of all 1953 Clair Patterson puts Ireland. In 1654, Ussher pinpointed In 1687, a scientific approach Earth’s age at 4.55 billion years. the date of Earth’s creation to the to the problem was suggested night preceding Sunday October by Isaac Newton. He argued that Landscapes are continually 23, 4004 BCE. This date became it would take a large body like denuded and the debris virtually enshrined in Christian Earth about 50,000 years to cool deposited into the sea. culture when it was printed in if it were made of molten iron. many Bibles as part of the Old He derived this figure by scaling There is no vestige Testament chronology. up the cooling time taken for of a beginning and no a “globe of iron of an inch in Yet this process does not diameter, exposed red hot to prospect of an end. lead to loss of the land open air.” Newton had opened the door to a scientific challenge surface… to previous understandings of Earth’s formation. …because new continents are formed from materials Following Newton’s lead, French derived from previous naturalist Georges-Louis Leclerc, continents by the same Comte de Buffon, experimented with a large ball of red-hot iron, and endless processes. showed that if Earth were made of molten iron, it would take 74,832 years to cool. In private, Buffon thought that Earth must be far