4 THE MEASURE OF THINGS

百度搜索 A Short History of Nearly Everything 天涯 或 A Short History of Nearly Everything 天涯在线书库 即可找到本书最新章节.

    IF YOU HAD to select the least vivial stific field trip of all time, you could certainlydo worse than the French Royal Academy of Sces’ Peruvian expedition of 1735. Led by ahydrologist named Pierre Bouguer and a soldier-mathemati named Charles Marie de Lai arty of stists and adventurers who traveled to Peru with the purposeulating distahrough the Andes.

    At the time people had lately bee ied with a powerful desire to uand theEarth—to determine how old it was, and how massive, where it hung in space, and how it hade to be. The French party’s goal was to help settle the question of the circumferehe pla by measuring the length of one degree of meridian (or 1/360 of the distance aroundthe pla) along a line reag from Yarouqui, near Quito, to just beyond  what isnow Ecuador, a distance of about two hundred miles.

    1Almost at ohings began to g, sometimes spectacularly so. In Quito, the visitorssomehow provoked the locals and<var></var> were chased out of town by a mob armed with stones. Soohe expedition’s doctor was murdered in a misuanding over a woman. Thebotanist became deranged. Others died of fevers and falls. The third most senior member ofthe party, a man named Pierre Godin, ran off with a thirteen-year-old girl and could not beio return.

    At one point the group had to suspend work fht months while La ine rode off toLima to sort out a problem with their permits. Eventually he and Bouguer stopped speakingand refused to work together. Everywhere the dwindling party went it was met with thedeepest suspis from officials who found it difficult to believe that a group of Frenchstists would travel halfway around the world to measure the world. That made no seall. Two and a half turies later it still seems a reasonable question. Why didn’t the Frenchmake their measurements in Frand save themselves all the bother and disfort of theirAndean adventure?

    The answer lies partly with the fact that eighteenth-tury stists, the Fren particular,seldom did things simply if an absurdly demanding alternative was available, and partly ractical problem that had first arisen with the English astronomer Edmond Halley manyyears before—long before Bouguer and La ine dreamed of going to South America,much less had a reason for doing so.

    * Triangulation, their chosehod, ular teique based on the geometric fact that if you know thelength of one side of a triangle and the angles of two ers, you  work out all its other dimensions withoutleaving your chair. Suppose, by way of example, that you and I decided we wished to know how far it is to theMoon. Using triangulation, the first thing we must do is put some distaween us, so lets say fumentthat you stay in Paris and I go to Moscow ah look at the Moon at the same time. Now if you imagine aline eg the three principals of this exercise-that is, you and I and the Moon-it forms a triangle. Measurethe length of the baseliween you and me and the angles of our two ers and the rest  be simplycalculated. (Because the interiles of a triangle always add up to 180 degrees, if you know the sum of twoof the angles you  instantly calculate the third; and knowing the precise shape of a triangle and the length ofone side tells you the lengths of the other sides.) This was in fact the method use by a Greek astronomer,Hipparchus of Nicaea, in 150 B.C. to work out the Moons distance from Earth. At ground level, the principles ulatiohe same, except that the triangles dont reato space but rather are laid side to side on amap. In measuring a degree of meridian, the surveyors would create a sort of  les marg acrossthe landscape.

    Halley was an exceptional figure. In the course of a long and productive career, he was asea captain, a cartographer, a professor of geometry at the Uy of Oxford, deputytroller of the Royal Mint, astronomer royal, and ior of the deep-sea diving bell. Hewrote authoritatively on magism, tides, and the motions of the plas, and fondly on theeffects of opium. He ied the weather map and actuarial table, proposed methods f out the age of the Earth and its distance from the Sun, even devised a practicalmethod for keeping fish fresh out of season. The ohing he didn’t do, iingly enough,was discover the et that bears his name. He merely reized that the et he saw in1682 was the same ohat had been seen by others in 1456, 1531, and 1607. It didn’tbee Halley’s et until 1758, some sixteen years after his death.

    For all his achievements, however, Halley’s greatest tribution to human knowledge maysimply have been to take part in a modest stific wager with two other worthies of his day:

    Robert Hooke, who is perhaps best remembered now as the first person to describe a cell, andthe great and stately Sir Christopher Wren, who was actually an astronomer first and architectsed, though that is not often generally remembered now. In 1683, Halley, Hooke, andWren were dining in Londohe versation turo the motions of celestial objects.

    It was known that plas were ined to orbit in a particular kind of oval known as anellipse—“a very specifid precise curve,” to quote Richard Feynman—but it wasn’tuood why. Wren generously offered a prize worth forty shillings (equivalent to a coupleof weeks’ pay) to whichever of the men could provide a solution.

    Hooke, ell known for taking credit for ideas that weren’t necessarily his own,claimed that he had solved the problem already but deed now to share it oerestingand iive grounds that it would rob others of the satisfa of disc the answer forthemselves. He would instead “ceal it for some time, that others might know how to valueit.” If he thought any more oter, he left no evidence of it. Halley, however, becameed with finding the ao the point that the following year he traveled toCambridge and boldly called upon the uy’s Lucasian Professor of Mathematics, Isaaewton, in the hope that he could help.

    on was a decidedly odd figure—brilliant beyond measure, but solitary, joyless, pricklyto the point of paranoia, famously distracted (upon swinging his feet out of bed in the mhe would reportedly sometimes sit for hours, immobilized by the sudden rush of thoughts tohis head), and capable of the most riveting strangeness. He built his own laboratory, the firstat Cambridge, but then engaged in the most bizarre experiments. Once he ied a bodkin—a long needle of the sort used for sewiher—into his eye socket and rubbed it arouwixt my eye and the bone as o [the] backside of my eye as I could” just to see whatwould happen. What happened, miraculously, was nothing—at least nothing lasting. Onanother occasioared at the Sun for as long as he could bear, to determine what effect itwould have upon his vision. Again he escaped lasting damage, though he had to spend somedays in a darkened room before his eyes fave him.

    Set atop these odd beliefs and quirky traits, however, was the mind of a supreme genius—though even when w in ventional els he often showed a tendency topeculiarity. As a student, frustrated by the limitations of ventional mathematics, heied airely new form, the calculus, but then told no one about it for twenty-sevenyears. In like manner, he did work in optics that transformed our uanding of light andlaid the foundation for the sce of spectroscopy, and again chose not to share the results forthree decades.

    For all his brilliance, real sce ated for only a part of his is. At least half hisw life was giveo alchemy and wayward religious pursuits. These were not meredabblings but wholehearted devotions. He was a secret adherent of a dangerously hereticalsect called Arianism, whose principal te was the belief that there had been no Holy Trinity(slightly ironiewton’s college at Cambridge was Trinity). He spent endless hoursstudying the floor plan of the lost Temple of King Solomon in Jerusalem (teag himselfHebrew in the process, the better to s inal texts) in the belief that it held mathematicalclues to the dates of the sed ing of Christ and the end of the world. His attat toalchemy was no less ardent. In 1936, the eist John Maynard Keynes bought a trunk ofon’s papers at au and discovered with astonishment that they were overwhelminglypreoccupied not with optics or plaary motions, but with a single-minded quest to turn basemetals into precious ones. An analysis of a strand of on’s hair in the 1970s found ittained mercury—a of io alchemists, hatters, and thermometer-makersbut almost no one else—at a tration some forty times the natural level. It is perhapslittle wohat he had trouble remembering to rise in the m.

    Quite what Halley expected to get from him when he made his unannounced visit in August1684 we  only guess. But thanks to the later at of a on fidant, AbrahamDeMoivre, we do have a record of one of sce’s most historiters:

    In 1684 DrHalley came to visit at Cambridge [and] after they had some timetogether the Drasked him what he thought the curve would be that would bedescribed by the Plas supposing the force of attra toward the Sun to bereciprocal to the square of their distance from it.

    This was a refereo a pieathematiown as the inverse square law, which Halleywas vinced lay at the heart of the explanation, though he wasn’t sure exactly how.

    SrIsaac replied immediately that it would be an [ellipse]. The Doctor, struck withjoy &amp; amazement, asked him how he k. ‘Why,’ saith he, ‘I have calculatedit,’ whereupon DrHalley asked him for his calculation without farther delay,SrIsaac looked among his papers but could not find it.

    This was astounding—like someone saying he had found a cure for cer but couldn’tremember where he had put the formula. Pressed by Halley, on agreed to redo thecalculations and produce a paper. He did as promised, but then did much more. He retired fortwo years of intensive refle and scribbling, and at length produced his masterwork: thePhilosophiae Naturalis Principia Mathematiathematical Principles of NaturalPhilosophy, better known as the Principia .

    On a great while, a few times in history, a human mind produces an observation soacute and ued that people ’t quite decide which is the more amazing—the fact orthe thinking of it. Principia was one of those moments. It made on instantly famous. Forthe rest of his life he would be draped with plaudits and honors, being, among much else,the first person in Britain knighted for stific achievement. Even the great Germanmathemati Gottfried von Leibniz, with whom on had a long, bitter fight over priorityfor the iion of the calculus, thought his tributions to mathematics equal to all theaccumulated work that had preceded him. “he gods no mortal may approach,” wroteHalley in a sehat was endlessly echoed by his poraries and by many otherssince.

    Although the Principia has been called “one of the most inaccessible books ever written”

    (on iionally made it difficult so that he wouldn’t be pestered by mathematical“smatterers,” as he called them), it was a bea to those who could follow it. It not onlyexplained mathematically the orbits of heavenly bodies, but also identified the attractive forcethat got them moving in the first place—gravity. Suddenly every motion in the universe madesense.

    At Principia ’s heart were on’s three laws of motion (which state, very baldly, that athing moves in the dire in which it is pushed; that it will keep moving in a straight liil some other force acts to slow or deflect it; and that every a has an opposite andequal rea) and his universal law of gravitation. This states that every obje theuniverse exerts a tug on every other. It may not seem like it, but as you sit here now you arepulling everything around you—walls, ceiling, lamp, pet cat—toward you with your own little(indeed, very little) gravitational field. And these things are also pulling on you. It wason who realized that the pull of any two objects is, to quote Feynman again,“proportional to the mass of ead varies inversely as the square of the distaweenthem.” Put another way, if you double the distaween two objects, the attrabetween them bees four times weaker. This  be expressed with the formulaF = GmmR2which is of course way beyond anything that most of us could make practical use of, but atleast preciate that it is elegantly pact. A couple of brief multiplications, a simpledivision, and, bingo, you know yravitational position wherever you go. It was the firstreally universal law of nature ever propounded by a human mind, which is why on isregarded with suiversal esteem.

    Principia’s produ was not without drama. To Halley’s horror, just as work wasnearing pletioon and Hooke fell into dispute over the priority for the inversesquare law aon refused to release the crucial third volume, without which the firsttwo made little sense. Only with some frantic shuttle diplomad the most liberalapplications of flattery did Halley manage finally to extract the cluding volume from theerratic professor.

    Halley’s traumas were not yet quite over. The Royal Society had promised to publish thework, but now pulled out, g financial embarrassment. The year before the society hadbacked a costly flop called The History of Fishes , and they now suspected that the market fora book on mathematical principles would be less than clamorous. Halley, whose means werenot great, paid for the book’s publication out of his own pocket. on, as was his ,tributed nothing. To make matters worse, Halley at this time had just accepted a positionas the society’s clerk, and he was informed that the society could no longer afford to providehim with a promised salary of ￡50 per annum. He was to be paid instead in copies of TheHistory of Fishes .

    on’s laws explained so many things—the slosh and roll of o tides, the motions ofplas, why onballs trace a particular trajectory before thudding back to Earth, why wearen’t flung into space as the pla spih us at hundreds of miles an hour2—that ittook a while for all their implications to seep in. But one revelation became almostimmediately troversial.

    This was the suggestion that the Earth is not quite round. Acc to on’s theory,the trifugal force of the Earth’s spin should result in a slight flattening at the poles and a<var></var>bulging at the equator, which would make the pla slightly oblate. That meant that thelength of a degree wouldn’t be the same in Italy as it was in Scotland. Specifically, the lengthwould shorten as you moved away from the poles. This was not good news for those peoplewhose measurements of the Earth were based on the assumption that the Earth erfectsphere, which was everyone.

    For half a tury people had been trying to work out the size of the Earth, mostly bymaking very exag measurements. One of the first such attempts was by an Englishmathemati named Richard Norwood. As a young man Norwood had traveled to Bermudawith a diving bell modeled on Halley’s device, intending to make a fortune scooping pearlsfrom the seabed. The scheme failed because there were no pearls and anyway Norwood’s belldidn’t work, but Norwood was not oo waste an experience. In the early sevehtury Bermuda was well known among ships’ captains for being hard to locate. Theproblem was that the o was big, Bermuda small, and the navigational tools for dealingwith this disparity hopelessly ie. There wasn’t eve an agreed length for anautical mile. Over the breadth of ahe smallest miscalculations would beagnified so that ships often missed Bermuda-sized targets by dismaying margins. Norwood,whose first love was trigory and thus angles, decided t a little mathematical rigorto navigation and to that eermio calculate the length of a degree.

    Starting with his back against the Tower of London, Norwood spent two devoted yearsmarg 208 miles north to York, repeatedly stretg and measuring a length of  ashe went, all the while making the most meticulous adjustments for the rise and fall of the landand the meanderings of the road. The final step was to measure the angle of the Sun at York atthe same time of day and on the same day of the year as he had made his first measurement inLondon. From this, he reasoned he could determihe length of one degree of the Earth’smeridian and thus calculate the distance around the whole. It was an almost ludicrouslyambitious uaking—a mistake of the slightest fra of a degree would throw the wholething out by miles—but in fact, as Norwood proudly declaimed, he was accurate to “within astling”—or, more precisely, to within about six hundred yards. Iric terms, his figureworked out at 110.72 kilometers per degree of arc.

    In 1637, Norwood’s masterwork of navigation, The Seaman’s Practice , ublished andfound an immediate following. It went through seventeeions and was still in priy-five years after his death. Norwood returo Bermuda with his family, being a2How fast you are spinning depends on where you are. The speed of the Earth’s spin varies from a little over1,000 miles an hour at the equator to 0 at the poles.

    successful planter aing his leisure hours to his first love, trigory. He survivedthere for thirty-eight <mark></mark>years and it would be pleasing to report that he passed this span inhappiness and adulation. In fact, he didn’t. On the crossing from England, his two young sonswere placed in a  with the Reverend Nathaniel White, and somehow so successfullytraumatized the young vicar that he devoted much of the rest of his career to persegNorwood in any small way he could think of.

    Norwood’s two daughters brought their father additional pain by making poor marriages.

    One of the husbands, possibly incited by the vicar, tinually laid small charges againstNorwood in court, causing him much exasperation and atied trips acrossBermuda to defend himself. Finally in the 1650s witch trials came to Bermuda and Norwoodspent his final years in severe uhat his papers ory, with their aresymbols, would be taken as unications with the devil and that he would be treated to adreadful execution. So little is known of Norwood that it may in fact be that he deserved hisunhappy deing years. What is certainly true is that he got them.

    Meanwhile, the momentum for determining the Earth’s circumference passed to France.

    There, the astronomer Jean Picard devised an impressively plicated method ulation involving quadrants, pendulum clocks, zenith sectors, and telescopes (for the motions of the moons of Jupiter). After two years of trundling and triangulatinghis way across France, in 1669 he announced a more accurate measure of 110.46 kilometersfor one degree of arc. This was a great source of pride for the French, but it redicated onthe assumption that the Earth erfect sphere—whiewton now said it was not.

    To plicate matters, after Picard’s death the father-and-son team of Giovanni andJacques Cassied Picard’s experiments over a larger area and came up with results thatsuggested that the Earth was fatter not at the equator but at the poles—that on, in otherwords, was exactly wrong. It was this that prompted the Academy of Sces to dispatchBouguer and La io South America to take new measurements.

    They chose the Andes because they o measure he equator, to determihere really was a differen sphericity there, and because they reasohat mountainswould give them good sightlines. In fact, the mountains of Peru were so stantly lost incloud that the team often had to wait weeks for an hour’s clear surveying. On top of that, theyhad selected one of the most nearly impossible terrains oh. Peruvians refer to theirlandscape as muy actado —“much acted”—and this it most certainly is. TheFrench had not only to scale some of the world’s most challenging mountains—mountainsthat defeated even their mules—but to reach the mountains they had to ford wild rivers, hacktheir way through jungles, and iles of high, sto, nearly all of it uncharted andfar from any source of supplies. But Bouguer and La ine were nothing if nottenacious, and they stuck to the task for nine and a half long, grim, sun-blistered years.

    Shortly before cluding the project, they received word that a sed French team, takingmeasurements in northern Sdinavia (and fag notable disforts of their own, fromsquelg bogs to dangerous ice floes), had found that a degree was in fact longer hepoles, as on had promised. The Earth was forty-three kilometers stouter when measuredequatorially than when measured from top to bottom around the poles.

    Bouguer and La ihus had spent nearly a decade w toward a result theydidn’t wish to find only to learn now that they weren’t even the first to find it. Listlessly, theypleted their survey, which firmed that the first French team was correct. Then, still notspeaking, they returo the coast and took separate ships home.

    Something else jectured by on in the Principia was that a plumb bob hung near amountain would ine very slightly toward the mountain, affected by the mountain’sgravitational mass as well as by the Earth’s. This was more than a curious fact. If youmeasured the defle accurately and worked out the mass of the mountain, you couldcalculate the universal gravitational stant—that is, the basic value of gravity, known asG—and along with it the mass of the Earth.

    Bouguer and La ine had tried this on Peru’s Mount Chimborazo, but had beeed by both the teical difficulties and their own squabbling, and so the notion laydormant for ahirty years until resurrected in England by Nevil Maskelyheastronomer royal. In Dava Sobel’s popular book Longitude, Maskelyne is presented as a ninnyand villain for failing to appreciate the brilliance of the aker John Harrison, and thismay be so, but we are ied to him in other ways not mentioned in her book, not least forhis successful scheme to weigh the Earth. Maskelyne realized that the nub of the problem laywith finding a mountain of suffitly regular shape to judge its mass.

    At his urging, the Royal Society agreed to engage a reliable figure to tour the British Islesto see if such a mountain could be found. Maskelyne knew just such a persoronomer and surveyor Charles Mason. Maskelyne and Mason had bee friends elevenyears earlier while engaged in a projeeasure an astronomical event of great importance:

    the passage of the pla Venus across the face of the Sun. The tireless Edmond Halley hadsuggested years before that if you measured one of these passages from selected points oh, you could use the principles ulation to work out the distao the Sun, andfrom that calibrate the distao all the other bodies in the solar system.

    Unfortunately, transits of Venus, as they are known, are an irregular occurreheye in pairs eight years apart, but then are absent for a tury or more, and there were nonein Halley’s lifetime.

    3But the idea simmered and when the ransit came due in 1761,nearly two decades after Halley’s death, the stific world was ready—indeed, more readythan it had been for an astronomical event before.

    With the instinct for ordeal that characterized the age, stists set off for more than ahundred locations around the globe—to Siberia, a, South Africa, Indonesia, and thewoods of Wissin, among many others. France dispatched thirty-two observers, Britaieen more, and still others set out from Sweden, Russia, Italy, Germany, Ireland, andelsewhere.

    It was history’s first cooperative iional stifiture, and almost everywhere itran into problems. Many observers were waylaid by war, siess, or shipwreck. Others madetheir destinations but opeheir crates to find equipment broken or ed by tropical heat.

    Once again the French seemed fated to provide the most memorably unlucky partits.

    Jean Chappe spent months traveling to Siberia by coach, boat, and sleigh, nursing his delicateinstruments over every perilous bump, only to find the last vital stretch blocked by swollen3The ransit will be on June 8, 2004, with a sed in 2012. There were none iweh tury.

    rivers, the result of unusually heavy spring rains, which the locals were swift to blame on himafter they saw him pointing strange instruments at the sky. Chappe mao escape withhis life, but with no useful measurements.

    Unluckier still was Guillaume Le Gentil, whose experiences are wonderfully summarizedby Timothy Ferris in ing of Age in the Milky Way . Le Gentil set off from France a yearahead of time to observe the transit from India, but various setbacks left him still at sea on theday of the transit—just about the worst place to be sieady measurements wereimpossible on a pitg ship.

    Undaunted, Le Gentil tinued on to India to await the ransit in 1769. With eightyears to prepare, he erected a first-rate viewing statioed aed his instruments,and had everything in a state of perfect readiness. On the m of the sed transit, June4, 1769, he awoke to a fine day, but, just as Venus began its pass, a cloud slid in front of theSun and remaihere for almost exactly the duration of the transit: three hours, fourteenminutes, and seven seds.

    Stoically, Le Gentil packed up his instruments a off for the  port, but en routehe tracted dysentery and wabbr></abbr>s laid up for nearly a year. Still weakened, he finally made itonto a ship. It was nearly wrecked in a hurrie off the Afri coast. When at last hereached home, eleven and a half years after setting off, and having achieved nothing, hediscovered that his relatives had had him declared dead in his absend hadenthusiastically plundered his estate.

    In parison, the disappois experienced by Britaieen scattered observerswere mild. Mason found himself paired with a young surveyor named Jeremiah Dixon andapparently they got along well, for they formed a lasting partnership. Their instrus wereto travel to Sumatra and chart the transit there, but after just one night at sea their ship wasattacked by a French frigate. (Although stists were in an iionally cooperativemood, nations weren’t.) Mason and Dixo a o the Royal Society  that itseemed awfully dangerous on the high seas and w if perhaps the whole thingoughtn’t to be called off. In reply they received a swift and chilly rebuke, noting that they hadalready been paid, that the nation and stifiunity were ting on them, and thattheir failure to proceed would result in the irretrievable loss of their reputations. Chastehey sailed on, but en route word reached them that Sumatra had fallen to the Frend sothey observed the transit inclusively from the Cape of Good Hope. On the way home theystopped on the lonely Atlantic outcrop of St. Helena, where they met Maskelyne, whoseobservations had been thwarted by cloud cover. Mason and Maskelyne formed a solidfriendship and spent several happy, and possibly even mildly useful, weeks charting tidalflows.

    Soon afterward, Maskelyuro England where he became astronomer royal, andMason and Dixon—now evidently more seasoned—set off for four long and often perilousyears surveying their way through 244 miles of dangerous Ameri wildero settle aboundary dispute betweeates of William Penn and Lord Baltimore and theirrespective ies of Pennsylvania and Maryland. The result was the famous Mason andDixon line, which later took on symbolic importance as the dividing liween the slaveand free states. (Although the line was their principal task, they also tributed severalastronomical surveys, including one of the tury’s most accurate measurements of a degreeof meridian—an achievement that brought them far more acclaim in England thatlingof a boundary dispute between spoiled aristocrats.)Ba Europe, Maskelyne and his terparts in Germany and France were forced to theclusion that the transit measurements of 1761 were essentially a failure. One of theproblems, ironically, was that there were too many observations, which when broughttogether often proved tradictory and impossible to resolve. The successful charting of aVenusian transit fell io a little-known Yorkshire-born sea captain named James Cook,who watched the 1769 transit from a sunny hilltop in Tahiti, and the on to chart andclaim Australia for the British . Upon his return there was now enough information forthe French astronomer Joseph Lalao calculate that the mean distance from the Earth tothe Sun was a little over 150 million kilometers. (Two further transits in the eeury allowed astroo put the figure at 149.59 million kilometers, where it hasremained ever sihe precise distance, we now know, is 149.597870691 millionkilometers.) The Earth at last had a position in space.

    As for Mason and Dixon, they returo England as stific heroes and, for reasonsunknown, dissolved their partnership. sidering the frequency with which they turn up atsemis ieenth-tury sce, remarkably little is known about either man. Nolikenesses exist and few written references. Of Dixon the Diary of National Biographynotes intriguingly that he was “said to have been born in a ine,” but then leaves it to thereader’s imagination to supply a plausible explanatory circumstance, and adds that he died atDurham in 1777. Apart from his name and long association with Mason, nothing more isknown.

    Mason is only slightly less shadowy. We know that in 1772, at Maskelyne’s behest, heaccepted the ission to find a suitable mountain for the gravitational defleexperiment, at length rep back that the mountain they needed was in the tral ScottishHighlands, just above Loch Tay, and was called Schiehallion. Nothing, however, wouldinduce him to spend a summer surveying it. He never returo the field again. His known movement was in 1786 when, abruptly and mysteriously, he turned up in Philadelphiawith his wife a children, apparently on the verge of destitution. He had not been baerica sinpleting his survey there eighteen years earlier and had no known reasonfor being there, or any friends or patrons to greet him. A few weeks later he was dead.

    With Mason refusing to survey the mountain, the job fell to Maskelyne. So for four monthsin the summer of 1774, Maskelyne lived in a tent in a remote Scottish glen and spent his daysdireg a team of surveyors, who took hundreds of measurements from every possibleposition. To find the mass of the mountain from all these numbers required a great deal oftedious calculating, for which a mathemati named Charles Hutton was ehesurveyors had covered a map with scores of figures, each marking aion at some pointon or around the mountain. It was essentially just a fusing mass of numbers, but Huttonnoticed that if he used a pencil to ect points of equal height, it all became much moreorderly. Indeed, one could instantly get a sense of the overall shape and slope of the mountain.

    He had ied tour lines.

    Extrapolating from his Schiehallion measurements, Hutton calculated the mass of the Earthat 5,000 million million tons, from which could reasonably be deduced the masses of all theother major bodies in the solar system, including the Sun. So from this one experiment welearhe masses of the Earth, the Sun, the Moon, the other plas and their moons, and gottour lines into the bargain—not bad for a summer’s work.

    Not everyone was satisfied with the results, however. The shorting of the Schiehallionexperiment was that it was not possible to get a truly accurate figure without knowing theactual density of the mountain. For venience, Hutton had assumed that the mountain hadthe same density as ordinary stone, about 2.5 times that of water, but this was little more thanan educated guess.

    One improbable-seeming person who turned his mind to the matter was a try parsonnamed John Michell, who resided in th<tt></tt>e lonely Yorkshire village of Thornhill. Despite hisremote and paratively humble situation, Michell was one of the great stific thinkers ofthe eighteenth tury and much esteemed for it.

    Among a great deal else, he perceived the wavelike nature of earthquakes, ducted muchinal researto magism and gravity, and, quite extraordinarily, envisiohepossibility of black holes two hundred years before anyone else—a leap of intuitive deduthat not eveon could make. When the German-born musi William Herscheldecided his real i in life was astronomy, it was Michell to whom he turned forinstru in making telescopes, a kindness for which plaary sce has been in his debtever since.

    4But of all that Michell aplished, nothing was more ingenious or had greater impactthan a mae he designed and built for measuring the mass of the Earth. Unfortunately, hedied before he could duct the experiments and both the idea and the necessary equipmentwere passed on to a brilliant but magnifitly retiring London stist named Henrydish.

    dish is a book in himself. Born into a life of sumptuous privilege—his grandfatherswere dukes, respectively, of Devonshire a—he was the most gifted English stistof his age, but also the stra. He suffered, in the words of one of his few biographers,from shyo a “degree b on disease.” Any human tact was for him a source ofthe deepest disfort.

    Once he opened his door to find an Austrian admirer, freshly arrived from Vienna, on thefront step. Excitedly the Austrian began to babble out praise. For a few moments dishreceived the pliments as if they were blows from a blunt objed then, uo takeany more, fled dowh and out the gate, leaving the front door wide open. It was somehours before he could be coaxed back to the property. Even his housekeeper unicatedwith him by letter.

    Although he did sometimes veo society—he articularly devoted to the weeklystific soirées of the great naturalist Sir Joseph Banks—it was always made clear to theuests that dish was on no at to be approached or even looked at. Thosewho sought his views were advised to wander into his viity as if by act and to “talk as4In 1781 Herschel became the first person in the modero discover a pla. He wao call it Gee,after the British monarch, but was overruled. Instead it became Uranus.

    it were into vacy.” If their remarks were stifically worthy they might receive amumbled reply, but more often than not they would hear a peeved squeak (his voice appearsto have been high pitched) and turn to find an actual vad the sight of dishfleeing for a more peaceful er.

    His wealth and solitary inations allowed him to turn his house in Clapham into a largelaboratory where he could range undisturbed through every er of the physical sces—electricity, heat, gravity, gases, anything to do with the position of matter. The sedhalf of the eighteenth tury was a time when people of a stifit grew intenselyied in the physical properties of fual things—gases aricity inparticular—and began seeing what they could do with them, often with more enthusiasm thansense. In America, Benjamin Franklin famously risked his life by flying a kite in aricalstorm. In France, a chemist named Pilatre de Rozier tested the flammability of hydrogen bygulping a mouthful and blowing across an open flame, proving at a stroke that hydrogen isindeed explosively bustible and that eyebrows are not necessarily a perma feature ofone’s face. dish, for his part, ducted experiments in which he subjected himself tograduated jolts of electrical current, diligently noting the increasing levels of agony until hecould keep hold of his quill, and sometimes his sciousness, no longer.

    In the course of a long life dish made a string of signal discoveries—among muchelse he was the first person to isolate hydrogen and the first to bine hydrogen and oxygento form water—but almost nothing he did was entirely divorced from strangeness. To thetinuing exasperation of his fellow stists, he often alluded in published work to theresults of ti experiments that he had not told anyone about. In his secretiveness hedidn’t merely resemble on, but actively exceeded him. His experiments with electricalductivity were a tury ahead of their time, but unfortunately remained undiscovereduntil that tury had passed. Ihe greater part of what he did wasn’t known until thelate eenth tury when the Cambridge physicist James Clerk Maxwell took oaskof editing dish’s papers, by which time credit had nearly always been given to others.

    Among much else, and without telling anyone, dish discovered or anticipated the lawof the servation of energy, Ohm’s law, Dalton’s Law of Partial Pressures, Richter’s Lawof Reciprocal Proportions, Charles’s Law of Gases, and the principles of electricalductivity. That’s just some of it. Acc to the sce historian J. G. Crowther, he alsoforeshadowed “the work of Kelvin and G. H. Darwin on the effect of tidal fri on slowiation of the earth, and Larmor’s discovery, published in 1915, on the effect of localatmospheric cooling . . . the work of Pickering on freezing mixtures, and some of the work ofRooseboom oerogeneous equilibria.” Finally, he left clues that led directly to thediscovery of the group of elements known as the noble gases, some of which are so elusivethat the last of them wasn’t found until 1962. But our i here is in dish’s lastknown experiment when ie summer of 1797, at the age of sixty-seveurned hisattention to the crates of equipment that had beeo him—evidently out of simplestific respect—by John Michell.

    When assembled, Michell’s apparatus looked like nothing so much as aeenth-tury version of a Nautilus weight-training mae. It incorporated weights,terweights, pendulums, shafts, and torsion wires. At the heart of the mae were two350-pound lead balls, which were suspended beside two smaller spheres. The idea was tomeasure the gravitational defle of the smaller spheres by the larger ones, which wouldallow the first measurement of the elusive forown as the gravitational stant, and fromwhich the weight (strictly speaking, the mass)5of the Earth could be deduced.

    Because gravity holds plas in orbit and makes falling objects land with a bang, we tendto think of it as a powerful force, but it is not really. It is only powerful in a kind of collectivesense, when one massive object, like the Sun, holds on to another massive object, like theEarth. At aal level gravity is extraordinarily unrobust. Each time you pick up a bookfrom a table or a dime from the floor you effortlessly overe the bined gravitatioion of aire pla. What dish was trying to do was measure gravity at thisextremely featherweight level.

    Delicacy was the key word. Not a whisper of disturbance could be allowed into the roomtaining the apparatus, so dish took up a position in an adjoining room and made hisobservations with a telescope aimed through a peephole. The work was incredibly exagand involved seventeen delicate, interected measurements, which together took nearly ayear to plete. When at last he had finished his calculations, dish annouhat theEarth weighed a little over 13,000,000,000,000,000,000,000 pounds, or six billion trillioris, to use the modern measure. (A metri is 1,000 kilograms or 2,205 pounds.)Today, stists have at their disposal maes so precise they  detect the weight of asingle bacterium and so sensitive that readings  be disturbed by someone yawniy-five feet away, but they have not signifitly improved on dish’s measurements of1797. The curre estimate for Earth’s weight is 5.9725 billion trillioris, adifference of only about 1 pert from dish’s finding. Iingly, all of this merelyfirmed estimates made by on 110 years before dish without any experimentalevide all.

    So, by the late eighteenth tury stists knew very precisely the shape and dimensionsof the Earth and its distance from the Sun and plas; and now dish, without evenleaving home, had gives weight. So you might think that determining the age of theEarth would be relatively straightforward. After all, the necessary materials were literally attheir feet. But no. Human beings would split the atom and ielevision, nylon, and instantcoffee before they could figure out the age of their own pla.

    To uand why, we must travel north to Scotland and begin with a brilliant and genialman, of whom few have ever heard, who had just ied a new sce called geology.

    5To a physicist, mass a are two quite different things. Your mass stays the same wherever you go, butyour weight varies depending on how far you are from the ter of some other massive object like a pla.

    Travel to the Moon and you will be much lighter but no less massive. Oh, for all practical purposes, massa are the same and so the terms  be treated as synonymous. at least outside the classroom.

百度搜索 A Short History of Nearly Everything 天涯 或 A Short History of Nearly Everything 天涯在线书库 即可找到本书最新章节.