万物简史英文版_比尔·布莱森-第12章
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ults of contingent experiments that he had not told anyone about。 in his secretiveness hedidn鈥檛 merely resemble newton； but actively exceeded him。 his experiments with electricalconductivity were a century ahead of their time； but unfortunately remained undiscovereduntil that century had passed。 indeed the greater part of what he did wasn鈥檛 known until thelate nineteenth century when the cambridge physicist james clerk maxwell took on the taskof editing cavendish鈥檚 papers； by which time credit had nearly always been given to others。
among much else； and without telling anyone； cavendish discovered or anticipated the lawof the conservation of energy； ohm鈥檚 law； dalton鈥檚 law of partial pressures； richter鈥檚 lawof reciprocal proportions； charles鈥檚 law of gases； and the principles of electricalconductivity。 that鈥檚 just some of it。 according to the science historian j。 g。 crowther； he alsoforeshadowed 鈥渢he work of kelvin and g。 h。 darwin on the effect of tidal friction on slowingthe rotation of the earth； and larmor鈥檚 discovery； published in 1915； on the effect of localatmospheric cooling 。 。 。 the work of pickering on freezing mixtures； and some of the work ofrooseboom on heterogeneous equilibria。鈥潯inally； 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鈥檛 found until 1962。 but our interest here is in cavendish鈥檚 lastknown experiment when in the late summer of 1797； at the age of sixty…seven； he turned hisattention to the crates of equipment that had been left to him鈥攅vidently out of simplescientific respect鈥攂y john michell。
when assembled； michell鈥檚 apparatus looked like nothing so much as an eighteenth…century version of a nautilus weight…training machine。 it incorporated weights；counterweights； pendulums； shafts； and torsion wires。 at the heart of the machine were two350…pound lead balls； which were suspended beside two smaller spheres。 the idea was tomeasure the gravitational deflection of the smaller spheres by the larger ones； which would allow the first measurement of the elusive force known as the gravitational constant； and fromwhich the weight （strictly speaking； the mass）5of the earth could be deduced。
because gravity holds planets 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 an elemental 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 gravitationalexertion of an entire planet。 what cavendish 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 roomcontaining the apparatus； so cavendish took up a position in an adjoining room and made hisobservations with a telescope aimed through a peephole。 the work was incredibly exactingand involved seventeen delicate； interconnected measurements； which together took nearly ayear to plete。 when at last he had finished his calculations； cavendish announced that theearth weighed a little over 13；000；000；000；000；000；000；000 pounds； or six billion trillionmetric tons； to use the modern measure。 （a metric ton is 1；000 kilograms or 2；205 pounds。）today； scientists have at their disposal machines so precise they can detect the weight of asingle bacterium and so sensitive that readings can be disturbed by someone yawning seventy…five feet away； but they have not significantly improved on cavendish鈥檚 measurements of1797。 the current best estimate for earth鈥檚 weight is 5。9725 billion trillion metric tons； adifference of only about 1 percent from cavendish鈥檚 finding。 interestingly； all of this merelyconfirmed estimates made by newton 110 years before cavendish without any experimentalevidence at all。
so； by the late eighteenth century scientists knew very precisely the shape and dimensionsof the earth and its distance from the sun and planets； and now cavendish； without evenleaving home； had given them its 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 invent television； nylon； and instantcoffee before they could figure out the age of their own planet。
to understand why； we must travel north to scotland and begin with a brilliant and genialman； of whom few have ever heard； who had just invented a new science called geology。
5to a physicist； mass and weight are two quite different things。 your mass stays the same wherever you go； butyour weight varies depending on how far you are from the center of some other massive object like a planet。
travel to the moon and you will be much lighter but no less massive。 on earth； for all practical purposes； massand weight are the same and so the terms can be treated as synonymous。 at least outside the classroom。
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5 THE STONE…BREAKERS
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at just the time that henry cavendish was pleting his experiments in london； fourhundred miles away in edinburgh another kind of concluding moment was about to take placewith the death of james hutton。 this was bad news for hutton； of course； but good news forscience as it cleared the way for a man named john playfair to rewrite hutton鈥檚 work withoutfear of embarrassment。
hutton was by all accounts a man of the keenest insights and liveliest conversation； a delightin pany； and without rival when it came to understanding the mysterious slow processesthat shaped the earth。 unfortunately； it was beyond him to set down his notions in a form thatanyone could begin to understand。 he was； as one biographer observed with an all but audiblesigh； 鈥渁lmost entirely innocent of rhetorical acplishments。鈥潯early every line he pennedwas an invitation to slumber。 here he is in his 1795 masterwork； a theory of the earth withproofs and illustrations ； discussing 。 。 。 something：
the world which we inhabit is posed of the materials； not of the earth whichwas the immediate predecessor of the present； but of the earth which； in ascendingfrom the present； we consider as the third； and which had preceded the land thatwas above the surface of the sea； while our present land was yet beneath the waterof the ocean。
yet almost singlehandedly； and quite brilliantly； he created the science of geology andtransformed our understanding of the earth。 hutton was born in 1726 into a prosperousscottish family； and enjoyed the sort of material fort that allowed him to pass much of hislife in a genially expansive round of light work and intellectual betterment。 he studiedmedicine； but found it not to his liking and turned instead to farming； which he followed in arelaxed and scientific way on the family estate in berwickshire。 tiring of field and flock； in1768 he moved to edinburgh； where he founded a successful business producing salammoniac from coal soot； and busied himself with various scientific pursuits。 edinburgh atthat time was a center of intellectual vigor； and hutton luxuriated in its enriching possibilities。
he became a leading member of a society called the oyster club； where he passed hisevenings in the pany of men such as the economist adam smith； the chemist josephblack； and the philosopher david hume； as well as such occasional visiting sparks asbenjamin franklin and james watt。
in the tradition of the day； hutton took an interest in nearly everything； from mineralogy tometaphysics。 he conducted experiments with chemicals； investigated methods of coal miningand canal building； toured salt mines； speculated on the mechanisms of heredity； collectedfossils； and propounded theories on rain； the position of air； and the laws of motion；among much else。 but his particular interest was geology。
among the questions that attracted interest in that fanatically inquisitive age was one thathad puzzled people for a very long time鈥攏amely； why ancient clamshells and other marinefossils were so often found on mountaintops。 how on earth did they get there？ those whothought they had a solution fell into two opposing camps。 one group； known as theneptunists； was convinced that everything on earth； including seashells in improbably lofty places； could be explained by rising and falling sea levels。 they believed that mountains；hills； and other features were as old as the earth itself； and were changed only when watersloshed over them during periods of global flooding。
opposing them were the plutonists； who noted that volcanoes and earthquakes； amongother enlivening agents； continually changed the face of the planet but clearly owed nothing towayward seas。 the plutonists also raised awkward questions about where all the water wentwhen it wasn鈥檛 in flood。 if there was enough of it at times to cover the alps； then where； pray；was it during times of tranquility； such as now？ their belief was that the earth was subject toprofound internal forces as well as surface ones。 however； they couldn鈥檛 convincingly explainhow all those clamshells got up there。
it was while puzzling over these matters that hutton had a series of exceptional insights。
from looking at his own farmland； he could see that soil was created by the erosion of rocksand that particles of this soil were continually washed away and carried off by streams andrivers and redeposited elsewhere。 he realized that if such a process were carried to its naturalconclusion then earth would eventually be worn quite smooth。 yet everywhere around himthere were hills。 clearly there had to be some additional process； some form of renewal anduplift； that created new hills and mountains to keep the cycle going。 the marine fossils onmountaintops； he decided； had not been deposited during floods； but had risen along with themountains themselves。 he also deduced that it was heat within the earth that created newrocks and continents and thrust up mountain chains。 it is not too much to say that geologistswouldn鈥檛 grasp the full implications of this thought for two hundred years； when finally theyadopted plate tectonics。 above all； what hutton鈥檚 theories suggested was that earth processesrequired huge amounts of time； far more than anyone had ever dreamed。 there were enoughinsights here to transform utterly our understanding of the earth。
in 1785； hutton worked his ideas up into a long paper； which was read at consecutivemeetings of the royal society of edinburgh。 it attracted almost no notice at all。 it鈥檚 not hardto see why。 here； in part； is how he presented it to his audience：
in the one case； the forming cause is in the body which is separated； for； after thebody has been actuated by heat； it is by the reaction of the proper matter of thebody； that the chasm which constitutes the vein is formed。 in the other case； again；the cause is extrinsic in relation to the body in which the chasm is formed。 therehas been the most violent fracture and divulsion； but the cause is still to seek； andit appears not in the vein； for i
