Chapter 6 Chapter Four Determination of Things

Nature and nature's laws are hidden in the night; God said, let Newton be born!So the world is bright. --Alexander Pope If you were to pick the most unpleasant field scientific expedition ever made, you would be hard-pressed to pick one more unlucky than the Peruvian expedition of the French Royal Academy of Sciences in 1735.Led by a hydrologist named Pierre Bouguer and a military mathematician named Charlie Marie Condamine, a team of scientists and adventurers traveled to Peru with the aim of Determining distance across the Andes by triangulation. At that time, people were infected with a strong desire to understand the earth-to determine how old the earth is, how big it is, in what part of the universe it hangs, and how it was formed.The task of the French team was to measure the length of a meridian of 1 degree (1/360th of the Earth's circumference) along a straight line from Jaroqui, near Quito, to a point past Cuenca in present-day Ecuador , about 320 kilometers in length, thus helping to resolve the planet's circumference problem.

Things go wrong almost from the start, sometimes jaw-droppingly.In Quito, the visitors somehow angered the locals and were driven out of the city by a stone-carrying mob.Not long after, a doctor on the measurement team is murdered over a misunderstanding with a woman.The botanist in the group is insane.Others died of fever or fell to their deaths.Number three on the expedition—a man named Jean Godin—eloped with a 13-year-old girl and couldn't be persuaded to return. The survey team had to stop working for eight months at one point; meanwhile, Condamina rode to Lima to settle a permit problem.He and Booger ended up not talking to each other and refusing to cooperate.Everywhere the dwindling survey team went, local officials were suspicious.It was hard for them to believe that these French scientists would go halfway around the world in order to measure the world.It doesn't make sense at all.Two and a half centuries later, this still seems like a valid question.The French don't have to suffer so much and go to the Andes, why don't they just do measurements in France?

On the one hand, this is because eighteenth-century scientists, especially French scientists, rarely did things the easy way.On the other hand, this is related to a practical problem.The question arose many years ago—long before Bouguer and Condaminer dreamed of going to South America, let alone had a reason to do so—with British astronomer Edmund Halley. Harley was an extraordinary character.In a long and prolific career he was a sea captain, cartographer, professor of geometry at Oxford University, deputy master of the Royal Mint, astronomer royal and inventor of the bathyscaphe.He wrote authoritatively on magnetism, tides, and planetary motion, and naively on the effects of opium.He invented weather maps and tables, proposed methods for calculating the age of the Earth and the distance from the Earth to the sun, and even invented a practical method for keeping fish fresh until out of season.The only thing he didn't do was discover the comet that bears his name.He simply admitted that the comet he had seen in 1682 was the same comet seen by others in 1456, 1531, and 1607.

The comet wasn't named Halley's Comet until 1758, about 16 years after his death. Yet for all his accomplishments, perhaps his greatest contribution to human knowledge lay in his participation in a scientific bet.The stakes were low, and the opponents were two other luminaries of the era.One is Robert Hooke, who is perhaps best remembered now for describing the cell; the other is the great and majestic Sir Christopher Wren, who was actually first an astronomer and later an architect. Teacher, although people often don't remember this much now. In 1683 Halley, Hooke and Wren were dining in London when suddenly the conversation turned to celestial motions.It is thought that planets tend to tend to orbit in a particular ellipse - in Richard Feynman's words, "a particular and precise curve" - ​​but it is not known what reason.Wren generously offered to give a prize worth 40 shillings (the equivalent of two weeks' wages) to any of them who could find an answer.

Hooker is known for his extravagance, though some opinions may not necessarily be his own.He claims he has solved the problem, but is reluctant to share it now, for an interesting and ingenious reason, saying that by doing so he will deprive others of the opportunity to find out for themselves.Therefore, he wants to "keep the answer secret for a period of time, so that others will know how to value it".There is no indication that he thought about it again afterward.However, Halley was fascinated and determined to find the answer. He also went to Cambridge University the next year to visit Isaac Newton, a professor of mathematics at the university, hoping to get his help.

Newton is definitely a weirdo-he is brilliant, but reclusive, dull, sensitive, suspicious, and inattentive (it is said that after he sticks his feet out of the bed in the morning, he sometimes has a sudden rush of thoughts and will be motionless. sit for hours), and do very interesting oddities.He set up his own laboratory, the first at Cambridge University, but then went on to engage in unusual experiments.On one occasion, he inserted a large eye-of-needle needle -- a long needle used to sew leather -- into the eye socket and rubbed it "between the eye and the bone as close as possible to the back of the eye," with the aim of Just to see what happens.The result, oddly enough, was nothing—at least not with lasting consequences.Another time he stared wide-eyed at the sun for as long as he could, in order to discover what was affecting his vision.Again he was not seriously injured, although he had to spend a few days in a dark room while his eyes healed.

These bizarre beliefs and eccentric traits were nothing compared to his extraordinary genius - even when working in conventional ways, he often seemed special.When he was a student, he felt that ordinary mathematics was very limited and was very disappointed, so he invented a brand new form-calculus, but he didn't tell anyone about it for 27 years.He worked in optics in the same way, changing our understanding of light and laying the groundwork for spectroscopy, but it took 30 years before he shared his results with others. As smart as he was, real science was only a part of his interest.He spent at least half his working years in alchemy and capricious religious practices.These activities are not dabbles, but plunge into them wholeheartedly.He secretly practiced a very dangerous pagan religion called Arianism.The main teaching of the church is that there is no Trinity at all (which is somewhat ironic, since Newton's workplace was Trinity College, Cambridge University).He spent countless hours studying the plans of the defunct King Solomon's Temple in Jerusalem (teaching himself Hebrew in the process so he could read the work in its original language), thinking he held the mathematical clue that Christ's second The date of Advent and the end of the world.He was equally enthusiastic about alchemy. In 1936, the economist John Maynard bought a box of Newton's papers at auction and was astonished to find that most of the material had nothing to do with optics or planetary motion, but rather with his quest to convert cheap metals Materials that become precious metals. In the 1970s, analysis of a lock of Newton's hair revealed that it contained mercury -- an element of little interest to anyone but alchemists, hatters and thermometer makers -- at about the average human concentration 40 times.It is perhaps not surprising that he has a problem with getting up unexpectedly in the morning.

In August 1684, Halley came to visit Newton uninvited.What help he was counting on from Newton, we can only guess.But thanks to a later account written by one of Newton's close friends, Abraham Demofort, we have an account of one of the most historic meetings in science: In 1684, Dr. Halley visited Cambridge.After they had been together for a while, the doctor asked him what he thought the curves of the planets would look like if the gravitational force of the sun was inversely proportional to the square of the planet's distance from the sun. What is mentioned here is a mathematical problem called the inverse square law.Halley firmly believed that this was the key to explaining the problem, although he was not sure of its subtleties.

Isaac Newton immediately replied that it would be an ellipse.The doctor was delighted and surprised, and asked him how he knew. "Gee," he said, "I've already done the calculations." Dr. Halley immediately asked for his calculations.Sir Isaac rummaged for a while among the materials, but could not find them. This is startling - like someone who says he has found a cure for cancer but can't remember where he put the prescription.At Harley's urging, Newton promised to do the calculation again, and produced a piece of paper.He did as promised, but much more.For two years he shut himself up, pondering, scribbling and drawing, and finally came up with his masterpiece: The Mathematical Principles of Natural Philosophy, more commonly known as the Principia.

Very occasionally, and only a few times in history, someone makes an observation so keen and unexpected that one cannot be sure which is more startling—the fact or his thought. The advent of Principia was one such moment. It instantly made Newton famous.For the rest of his life he would live with praise and honor, notably being the first person in Britain to be knighted for scientific achievement.Even the great German mathematician Gottfried Leibniz believed that his contribution to mathematics was equal to the sum of all the achievements before him, although Newton had the same problem as the first to invent calculus. He fought long and hard. "No mortal man was nearer to God than Newton himself," wrote Halley with emotion.His contemporaries, and many others since, have felt the same way.

"Principia" has always been called "one of the most difficult books to understand" (Newton deliberately made it difficult so that he would not be entangled by what he called mathematics "laymen"), but for those who can understand , it is a bright light.It not only explains the orbits of celestial bodies from a mathematical point of view, but also points out the gravitational force that makes celestial bodies run - universal gravitation.Suddenly, every movement in the universe makes sense. At the heart of Principia are Newton's three laws of motion (the laws state very clearly that a body moves in the direction of the thrust; it keeps moving in a straight line until some other force acts to slow it down or change it direction; every action has an equal reaction) and his law of gravitation.This means that every object in the universe attracts every other object.It seems unlikely, but as you sit here, you are using your own small (really small) gravitational field to attract everything around you - walls, ceiling, lamps, pet cats.And these things are also attracting you.It was Newton who realized that the gravitational force of any two objects, again in Feynman's words, "is proportional to the mass of each object and varies as the inverse square of the distance between them".In other words, if you double the distance between two objects, the gravitational force between them is four times weaker.This can be expressed by the following formula: F=G This formula is of course of no practical use to most of us at all, but at least we appreciate its beauty, its simplicity.Wherever you go, just do two quick multiplications, one simple division, and hey, you know your gravitational status.It was the first truly universal law of nature proposed by man, and it is the reason why Newton is revered everywhere. Principia did not come about without drama.To Halley's astonishment, when the work was nearing completion, Newton and Hooke quarreled over who had invented the inverse square law first, and Newton refused to publish the crucial third volume, without which the first two volumes It doesn't make much sense.It was only after intense shuttle diplomacy and many good words that Halley finally managed to get the last volume from the eccentric professor. Harley's troubles weren't quite over.The Royal Society had originally agreed to publish the work, but now it backed down, saying it was in financial difficulty.The previous year the Society had gambled heavily on The History of Fishes, which had cost them nothing; they feared that a book on mathematical principles would not have much marketability.Halley, though not very wealthy, paid for the publication of the book out of his own pocket.As always, Newton paid nothing.To make matters worse, Halley had just accepted the position of clerk of the Society at this time, and he was told that the Society was unable to pay him the promised annual salary of £50, and could only pay with a few "History of Fishes". Newton's laws explain many things—the splashing and churning of tides in the ocean; the motion of planets; why cannonballs follow a certain trajectory before they hit the ground; We're not flung into space -- the full significance of these laws will take a long time to grasp.But what they revealed sparked controversy almost immediately. This means that the earth is not perfectly round.According to Newton's theory, the centrifugal force produced by the rotation of the earth caused the poles to be somewhat flattened and the equator to be somewhat bulged.Therefore, the planet is slightly oblate.This means that the length of 1 degree of longitude is not equal in Italy and Scotland.To be precise, the farther away from the poles, the shorter the length.That's not good news for those who measure the planet by thinking that Earth is a rounded sphere.Those people are everyone. In half a century, people wanted to measure the size of the earth, and most of them used very strict measurement methods.One of the first to attempt this was an English mathematician named Richard Norwood.Norwood had traveled to Bermuda as a young man with a diving bell modeled after Harley's, hoping to make a fortune fishing for pearls from the bottom of the sea.The plan didn't work out, since there were no pearls and Norwood's diving bell didn't work, but Norwood wasn't alone in wasting an experience. In the early 17th century, Bermuda was notoriously difficult to locate among captains.The problem is that the ocean is too big, Bermuda is too small, and the nautical instruments used to account for the discrepancy are woefully inadequate.Even the length of 1 nautical mile is different.With regard to the breadth of the sea, the slightest miscalculation becomes very large, so ships often fail to find targets the size of Bermuda with great error.Norwood was fond of trigonometry, and therefore triangles, and wanted to use a little mathematics in his navigation, so he decided to calculate the length of a meridian of 1 degree. With his back to the Tower of London, Norwood embarked on the journey, walking the 450 kilometers north to York over two years, endlessly straightening and measuring a chain as he went.In the process, he meticulously corrected the data to take into account the ups and downs of the land and the curves of the road.The final procedure is to measure the angle of the sun at York on the same day of the year and at the same time of day.He has taken his first measurements in London.From this measurement, he deduced, he could derive the length of the Earth's longitude of 1 degree, and thus calculate the entire circumference of the Earth.It was almost an ambitious endeavor - a single error in the length of 1 degree could vary the whole length by many kilometers - but in reality, as Norwood proudly endeavored to claim, his calculations were remarkably precise , by "minimally" -- or more precisely, a difference of less than 550 meters.Expressed in the metric system, he came up with a figure of 110.72 kilometers per degree of longitude. In 1637, Norwood's masterpiece of navigation, The Sailor's Practice, was published and immediately won a readership.It went into 17 reprints and is still in print 25 years after his death.Norwood returned to Bermuda with his family and became a successful plantation owner, spending his spare time with his beloved trigonometry.He lived there for 38 years.If you tell everyone that he has lived happily in the past 38 years and has been admired by people, everyone will be very happy.However, this is not the case.On the voyage after leaving England, his two young sons shared a cabin with the Reverend Nathaniel White, somehow traumatizing the young clergyman for much of the rest of his life. Find ways to trouble Norwood. Both of Norwood's daughters had unsatisfactory marriages, causing additional pain for their father.A son-in-law, probably at the clergyman's instigation, kept suing Norwood in court for petty matters, which irritated him so much that he was often obliged to defend himself on the other side of Bermuda.Finally, in the 1750s, when witch trials became popular in Bermuda, Norwood spent his final years in fear that his trigonometry treatises with their occult symbols would be seen as communicating with the devil, and that he would be horribly Sentenced to death.We don't know much about Norwood, but he spent his later years in unhappy circumstances and probably deserved it, anyway.It is certainly true that his old age was indeed spent in this way. Meanwhile, momentum for measuring the circumference of the Earth has reached France.There, astronomer Jean Picard developed an extremely complex method of triangulation, using sector plates, pendulum clocks, zenith quadrants, and telescopes (to observe the motions of Saturn's moons).He spent two years traveling across France, making triangulation measurements; afterward, he announced an even more precise measurement: 1 degree longitude is 110.46 kilometers.The French were very proud of this, but the result was based on the assumption that the earth was a sphere - and now Newton says the earth is not of that shape. To further complicate matters, Giovanni and Jacques Cassini repeated Picard's experiments on a larger area after Picard's death.They came up with results showing that the Earth bulges not at the equator, but at the poles—in other words, Newton was completely wrong.Because of this, the Academy of Sciences sent Bouguer and Condamine to South America to re-measure. They chose the Andes because they needed to measure closer to the equator to see if there really was a difference in roundness there, and because they thought the mountains provided better visibility.In fact, the mountains of Peru are often shrouded in clouds and fog, and the team often had to wait weeks for an hour of clear weather to take measurements.Not only that, they chose almost the most difficult terrain on earth.Peruvians call this terrain "very rare" -- and they're absolutely right.Not only did the two Frenchmen have to climb some of the most challenging mountains in the world--mountains that even their mules could not cross--but, to reach them, they had to ford several swift rivers, drill Through dense jungle and across kilometers of high pebble desert, places that are barely marked on maps, far from sources of supply.But Bouguer and Condamine were stoic.They were indomitable, not afraid of the wind and the sun, and persisted in carrying out their tasks, and spent nine and a half long years.Near the end of the project, word suddenly came to them that another French expedition was surveying northern Scandinavia (faced with its own hardships, from impenetrable swamps to perilous ice floes) , found that the 1-degree meridian is really longer near the two poles, just as Newton asserted.The earth is 43 kilometers thicker when measured at the equator than when it is measured from top to bottom around the poles. So it took Bouguer and Condamine nearly 10 years to arrive at a result they didn't expect, and found that it wasn't their first.They languidly ended up measuring, only to prove that the first French group was right.Then, they returned to the beach in silence, and set foot on their way home by boat. Another conjecture made by Newton in "Principles" is: a plumb line hanging near a mountain will be affected by the gravitational mass of the mountain and the earth, and tilt slightly towards the mountain.This speculation is very interesting.If you measure that deviation exactly, and calculate the mass of the mountain, you can figure out the gravitational constant -- the fundamental value of gravity, called G -- and you can also figure out the mass of the Earth. Bouguer and Condamine tried this on Chimborazo in Peru, but it was unsuccessful, partly because of the technical difficulty and partly because of their internal quarrels.So the matter was put on hold, only to be restarted 30 years later in England by Astronomer Royal Neville Maskelyne.Dava Sobel, in her bestseller The Warp, may be right when she describes Maskelyne as a fool and a villain who would not have appreciated the brilliance of clockmaker John Harrison.But we are indebted to Maskeline in other ways not mentioned in her book, especially for his successful scheme for weighing the earth. The crux of the problem, Maskelyne realized, was finding a regular-shaped mountain so that its mass could be estimated.At his urging, the Royal Society agreed to hire a trustworthy man to survey the British Isles to see if such a mountain could be found.Maskelyne happened to know just such a man—the astronomer and surveyor Charles Mason.Maskelyne and Mason became friends 11 years ago when they took on a project together to measure a major astronomical event: the transit of Venus.The indefatigable Edmund Halley had suggested some years ago that, by measuring this phenomenon once at selected locations on the earth, you could use the laws of triangulation to calculate the distance from the earth to the sun, and from this to calculate Distances to all other bodies in the solar system. Unfortunately, the so-called transit of Venus is an irregular event.The phenomenon comes in pairs, 8 years apart, and then doesn't happen once for a century or more.It didn't happen during Harley's lifetime. 1 However, the idea persists. In 1761, nearly 20 years after Halley's death, when the next transit of the sun came on time, the scientific community was ready -- more prepared than any previous astronomical phenomenon had been observed. With an instinct for hard work—a hallmark of the era—scientists traveled to more than 100 locations around the world—among them Siberia in Russia, China, South Africa, Indonesia, and the jungles of Wisconsin, USA.France sent 32 observers, Britain 18, and observers from Sweden, Russia, Italy, Germany, Iceland and other countries. It was the first internationally collaborative scientific effort in history, but it was fraught with difficulties almost everywhere.Many observers met with war, disease or shipwreck.Some arrived at their destination, but opened the box to find that the instrument was broken or bent by the scorching tropical sun.The French seemed doomed to yet another bad luck.It took Jean Chapey several months to reach Siberia by carriage, boat, and sleigh, and fragile instruments had to be carefully guarded at every bump.In the end, there was only a critical section of the journey left, but it was blocked by a swollen river.It turned out that not long before his arrival, there was a rare spring rain in the local area.The locals immediately blamed him, as they saw him pointing his bizarre instrument at the sky.Sharpe managed to escape with his life, but no meaningful measurements were made. Worse still was Guillaume Lettie, whose experience Timothy Ferriss described brilliantly and briefly in Growing Up in the Galaxy.Genti set out from France a year in advance to observe the transit in India, but encountered various setbacks and was still at sea on the day of the transit - which is almost the worst place to be since the measurements need to be in a steady state , and this simply cannot be done on a bumpy boat. Undaunted, Getti continued on to India to wait for the next transit in 1769.He had eight years to prepare, and thus built a first-class observatory, and he tested his instruments time and time again, making the preparations flawless. June 4, 1769 was the date of the second transit of the sun.When he woke up in the morning, he saw that it was a sunny day; however, just as Venus passed through the surface of the sun, a dark cloud blocked the sun and stayed there for 3 hours, 14 minutes and 7 seconds. The process of the day is over. Disappointed, Genti packed up his instruments and set out for the nearest port, where he contracted dysentery and was bedridden for nearly a year.In spite of his still weak health, he finally boarded a boat.The boat was nearly wrecked in a cyclone off the coast of Africa.After eleven and a half years away, he finally returned home.He finds nothing, only to find that his relatives have declared him dead, scrambling to seize his fortune. In comparison, the disappointment experienced by the 18 observers sent around the UK was nothing.Mason apparently got on well with a young surveyor named Jeremiah Dixon, and the two formed a lasting partnership.After they were ordered to go to India, they moved westward to Sumatra, where they drew transit maps.But their ship was attacked by a French frigate on the second night at sea. (While scientists are in a state of mind of international cooperation, countries are not. ) Mason and Dixon sent a text message to the Royal Society, saying that the high seas looked very dangerous and wondered if the whole plan should be cancelled.They soon received a chilling reply, which first scolded them, and then said that they had already taken the money, that the country and the scientific community had pinned their hopes on them, and that if they did not proceed with the plan, they would be ruined. The people of the country are disgraced. They changed their minds and continued on, but word came that Sumatra had fallen to the French.So they ended up observing this transit from the Cape of Good Hope, and it didn't work very well.On their way back home, they stopped briefly on St. Helena, a lonely island in the Atlantic Ocean, where they met Maskeline.Observations from Maskelyne were not possible due to cloud cover.Mason and Maskelyne struck up a strong friendship, charting trends together, and had a few happy, even meaningful weeks. Shortly thereafter, Maskelyne returned to England as Astronomers Royal, while Mason and Dixon - clearly more mature by this time - set off for America for four long and often dangerous years.They traversed 393 kilometers of treacherous wilderness, surveying along the way to resolve boundary disputes between the estates of William Penn and Lord Baltimore and between their respective colonies - Pennsylvania and Maryland.The result is that famous Mason-Dixon line.Later, this line was seen symbolically as the dividing line between slave and free states in the United States. (This line was their main task, but they also made several astronomical observations. On one occasion, they made the most accurate measurement of the length of a meridian of 1 degree at the time. For this achievement, they won much higher praise than for settling a border dispute between two spoiled aristocrats.) Back in Europe, Maskelyne and his German and French counterparts were forced to conclude that the transit observations of 1761 Basically failed.Ironically, one of the problems is that there are too many observations.Putting observations together often proves to be contradictory and impossible to unify.It was an unknown Yorkshire-born sea captain named James Cook who succeeded in charting the transit of Venus.He watched the transit of the sun in 1769 from a sun-soaked hilltop in Tahiti, and went on to map Australia and declare it a British crown colony.As soon as he returned to China, he heard that the French astronomer Joseph Lalande had calculated that the average distance from the earth to the sun was slightly more than 150 million kilometers. (There were two more transits in the 19th century, and astronomy derived a distance of 149.59 million kilometers. This figure has been maintained until now. We now know that the exact distance should be 1.495 978 706 91 million kilometers.) The earth is in space Finally, there is a position in the middle. Mason and Dixon return to England as scientific heroes; but, for reasons unknown, their partnership is irretrievably broken.Considering their frequent presence at major scientific events in the 18th century, it is remarkable how little is known about these two men.No photos, very little written information.As for Dixon, the Dictionary of British Names neatly mentions that he was "supposed to have been born in a coal mine," and then leaves the reader to his imagination to provide plausible explanations. The Dictionary goes on to say that he died in Durham in 1777.Nothing is known other than his name and his long-term partnership with Mason. There is a little more information about Mason's situation.We know that in 1772, at the request of Maskelyne, he was ordered to find a mountain for the measurement of gravitational deviation; at last, he sent back a report that the mountain they needed was located in the middle of the Scottish Highlands, just beside Loch Tay, named It's called Schiehallin Mountain.However, he would never spend a summer measuring it.He never returned to the scene.It is known that his next activity was in 1786.He suddenly and mysteriously shows up in Philadelphia with his wife and eight children, apparently impoverished and appalling.He hadn't been back to the Americas since completing his survey 18 years ago, and there was no apparent reason for his return, and no friends or patrons to greet him.A few weeks later, he died. Since Mason was reluctant to measure the mountain, the job fell to Maskelyne. For four months in the summer of 1774, Maskeline directed a team of surveyors from his tent in a remote Scottish glen.They took hundreds of measurements from every possible location.To derive the mass of the mountain from such a large amount of data requires a lot of tedious calculations.The man who undertook this work was a mathematician named Charles Hutton.Surveyors filled the map with dozens of data points, each indicating the height of a certain location on the mountain or its side.These numbers are really numerous and messy.However, Hutton noticed that as long as the points of equal height were connected with a pencil, everything appeared to be in order.In fact, right away you can tell the overall shape and slope of the mountain.So, he invented the contour line. From measurements at Schiehallin, Hutton calculated the mass of the Earth to be 5,000 trillion tons.On this basis, the mass of all major celestial bodies in the solar system including the sun can be deduced.Thus, from this experiment we learned the masses of the Earth, the Sun, the Moon, and the other planets and their satellites, and also invented contour lines—no small gain from a summer. However, not everyone is happy with the results.The downside of the Schiehalling experiment is that you don't know the true density of the mountain, so it's impossible to come up with a really exact number.For convenience, Hutton assumed that the density of the mountain was equal to that of ordinary stone, that is, about 2.5 times that of water, but this was only an empirical estimate. One person turned his attention to this problem.He was a countryman named John Michel, who lived in the sparsely populated village of Thornhill in Yorkshire.Despite the remoteness and simplicity of his environment, Michel was a great scientific thinker of the 18th century and was deeply respected. In particular, his recognition of the fluctuating nature of earthquakes, his enormously inventive work on magnetic fields and gravity, and his conceived of the existence of black holes 200 years before anyone else is quite remarkable -- not even Newton could have gotten that far. stride.When German-born musician Wilhelm Herschel decided that his real interest in life was astronomy, he turned to Michel for advice on how to build astronomical telescopes.The planetary science community has been indebted to him ever since. 1 Yet none of Michel's achievements was more ingenious or influential than an instrument of his own design and construction for measuring the mass of the earth.Unfortunately, he was not able to complete this experiment during his lifetime.The experiment, and the necessary equipment, were passed on to a distinguished and reclusive London scientist by the name of Henry Cavendish. Cavendish is a book in itself.Born into a wealthy and powerful family - grandfathers were the Dukes of Devonshire and Kent respectively - he was one of the most brilliant and extremely eccentric British scientists of his day.Several writers have written biographies of him.He was, in the words of one, "almost morbidly shy."He felt uncomfortable in contact with anyone, and even his housekeeper had to communicate with him by letter. Once he opened the door to find an Austrian admirer who had just arrived from Vienna standing on the front steps.The Austrian was very excited and was full of praise for him.一时之间，卡文迪许听着那个赞扬，仿佛挨了一记闷棍；接着，他再也无法忍受，顺着小路飞奔而去，出了大门，连前门也顾不得关上。几个小时以后，他才被劝说回家。 有时候，他也大胆涉足社交界--尤其热心于每周一次的由伟大的博物学家约瑟夫·班克斯举办的科学界聚会--但班克斯总是对别的客人讲清楚，大家决不能靠近卡文迪许，甚至不能看他一眼。那些想要听取他的意见的人被建议晃悠到他的附近，仿佛不是有意的，然后"只当那里没有人那样说话"。如果他们的话算得上是在谈论科学，他们也许会得到一个含糊的回答，但更经常的情形是听到一声怒气冲冲的尖叫（他好像一直是尖声尖气的），转过身来发现真的没有人，只见卡文迪许飞也似的逃向一个比较安静的角落。 卡文迪许钱又多，性格又孤僻，正好有条件把他在克拉彭的房子变成个大实验室，以便不受干扰地探索物理学的每个角落--电、热、引力、气体以及任何跟物质的性质有关的问题。18世纪末叶，是爱好科学的人们对基本物质--尤其是气体和电--的性质发生浓厚兴趣的时代，又是开始知道怎么对付它们的时代，但往往是热情有余，理智不足。在美国，本杰明·富兰克林不顾生命危险在大雷雨里放风筝，这是很有名的。在法国，一位名叫皮拉特尔·罗齐耶的化学家含了一口氢喷在明火上，以测试氢的可燃性，其结果是证明了氢确实是易爆物质，眉毛也不一定是人的脸上一个永久的特征。卡文迪许也做了许多实验，他曾经逐步加大在自己身上的电击强度，仔细体会逐渐厉害的痛苦，直到只拿得住手里的羽毛管，但有时候再也留不住自己的知觉。 在卡文迪许漫长的一生中，他取得了一系列重大发现--其中，他是分离氢的第一人，把氢和氧化合成水的第一人--但是，他所做的一切都脱离不了"古怪"两个字。他经常在出版的作品中提到从没有告诉过任何人的实验结果，这使他的科学家同行们老是很气恼。但是，尽管遮遮掩掩，他不光模仿牛顿，而且想要努力超过他。他对导电性能的实验超前了时代一个世纪，但不幸的是，直到那个世纪过去才被人发现。实际上，他的大部分成就直到19世纪末才为人所知。那个时候，剑桥大学物理学家詹姆斯·克拉克·麦克斯韦承担了编辑卡文迪许文献的任务。在此之前，发现虽然是他的，但功劳几乎总是别人的。 卡文迪许发现或预见到了能量守恒定律、欧姆定律、道尔顿的分压定律、里克特的反比定律、查理的气体定律以及电传导定律，但都没有告诉别人。这只是其中的一部分。据科学史家JG克劳瑟说，他还预见了"开尔文和GH达尔文关于潮汐摩擦对减慢地球自转速度的作用的成果、拉摩尔关于局部大气变冷的作用的发现（发表于1915年）......皮克林关于冷冻混合物的成就以及罗斯布姆关于异质平衡的某些成果"。最后，他还留下线索，直接导致一组名叫惰性气体的元素的发现。其中有几种是极难获得的，最后一种直到1962年才被发现。不过，我们现在的兴趣是卡文迪许所做的最后一次著名的试验。1797年夏末，67岁高龄的他把注意力转向约翰·米歇尔显然只是出于科学上的敬意留给他的几箱子设备。 装配完毕以后，米歇尔的仪器看上去很像是一台18世纪的鹦鹉螺牌举重练习机。它由重物、砝码、摆锤、轴和扭转钢丝组成。仪器的核心是两个635千克重的铅球，悬在两个较小球体的两侧。装配这台设备的目的是要测量两个大球给小球造成的引力偏差。这将使首次测量一种难以捉摸的力--所谓的引力常数--成为可能，并由此推测地球的重量（严格来说是质量）1。 引力使行星保持在轨道上，使物体砰然坠落，因此很容易被认为是一种强大的力，其实不然。它只是在整体意义上强大：一个巨大的物体，比如太阳，牵住另一个巨大的物体，比如地球。在基础的层面上，引力极小。每次你从桌子上拿起一本书，或从地板上拾起一枚硬币，你毫不费劲就克服了整个行星施加的引力。卡文迪许想要做的，就是在极轻的层面上测量引力。 精密是个关键词。设备所在的屋子里，容不得半点儿干扰。因此，卡文迪许就待在旁边的一间屋里，用望远镜瞄准一个窥孔来进行观察。这项工作是极其费劲的，要做17次精密而又互不关联的测量，他总共花了将近一年时间才完成。卡文迪许终于计算完毕，宣布地球的重量略略超过1300 000 000 000 000 000 000 000磅，用现代的计量单位来说就是6 000 000 000 000 000 000 000吨（1吨约等于2205磅）。 今天科学家手里的仪器，其精确度之高，可以测定一个细菌的重量；其灵敏度之高，有人在25米以外打个呵欠都会干扰读数。但是，他们对卡文迪许1797年的测量结果没有重大改动。目前对地球重量的最准确估计数是59725亿亿吨，与卡文迪许的结果只相差1％左右。 有意思的是，这一切都只是证实了在卡文迪许110年之前牛顿的估计，而且没有迹象表明牛顿做过任何试验。 无论如何，到18世纪末，科学家们已经知道地球的确切形状和大小，以及地球到太阳和各个行星的距离。连足不出户的卡文迪许都已算出了它们的重量。于是，你或许会认为，确定地球的年龄会是一件相对容易的事。毕竟，他们实际上已经掌握一切必要的资料。然而，实际情形并非如此。人类要等到能够分裂原子、发明电视、尼龙和速溶咖啡以后，才算得出我们自己这颗行星的年龄。 若要知道其中的原因，我们必须北上去一趟苏格兰，先去拜访一位杰出而又可亲的人。 这个人很少有人听说过，他刚刚发明了一门新学科：地质学。