按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
popularlyknown as eighteen hundred and froze to death。 morning frosts continued until june andalmost no planted seed would grow。 short of fodder； livestock died or had to be prematurelyslaughtered。 in every way it was a dreadful year鈥攁lmost certainly the worst for farmers inmodern times。 yet globally the temperature fell by only about 1。5 degrees fahrenheit。 earth鈥檚natural thermostat； as scientists would learn； is an exceedingly delicate instrument。
the nineteenth century was already a chilly time。 for two hundred years europe and northamerica in particular had experienced a little ice age； as it has bee known； whichpermitted all kinds of wintry events鈥攆rost fairs on the thames； ice…skating races along dutchcanals鈥攖hat are mostly impossible now。 it was a period； in other words； when frigidity wasmuch on people鈥檚 minds。 so we may perhaps excuse nineteenth…century geologists for beingslow to realize that the world they lived in was in fact balmy pared with former epochs；and that much of the land around them had been shaped by crushing glaciers and cold thatwould wreck even a frost fair。
they knew there was something odd about the past。 the european landscape was litteredwith inexplicable anomalies鈥攖he bones of arctic reindeer in the warm south of france； hugerocks stranded in improbable places鈥攁nd they often came up with inventive but not terribly plausible explanations。 one french naturalist named de luc； trying to explain how graniteboulders had e to rest high up on the limestone flanks of the jura mountains； suggestedthat perhaps they had been shot there by pressed air in caverns； like corks out of apopgun。 the term for a displaced boulder is an erratic； but in the nineteenth century theexpression seemed to apply more often to the theories than to the rocks。
the great british geologist arthur hallam has suggested that if james hutton； the father ofgeology； had visited switzerland； he would have seen at once the significance of the carvedvalleys； the polished striations； the telltale strand lines where rocks had been dumped； and theother abundant clues that point to passing ice sheets。 unfortunately； hutton was not a traveler。
but even with nothing better at his disposal than secondhand accounts； hutton rejected out ofhand the idea that huge boulders had been carried three thousand feet up mountainsides byfloods鈥攁ll the water in the world won鈥檛 make a boulder float； he pointed out鈥攁nd becameone of the first to argue for widespread glaciation。 unfortunately his ideas escaped notice； andfor another half century most naturalists continued to insist that the gouges on rocks could beattributed to passing carts or even the scrape of hobnailed boots。
local peasants； uncontaminated by scientific orthodoxy； knew better； however。 thenaturalist jean de charpentier told the story of how in 1834 he was walking along a countrylane with a swiss woodcutter when they got to talking about the rocks along the roadside。 thewoodcutter matter…of…factly told him that the boulders had e from the grimsel； a zone ofgranite some distance away。 鈥渨hen i asked him how he thought that these stones had reachedtheir location； he answered without hesitation： 鈥榯he grimsel glacier transported them on bothsides of the valley； because that glacier extended in the past as far as the town of bern。鈥櫋♀��
charpentier was delighted。 he had e to such a view himself； but when he raised thenotion at scientific gatherings； it was dismissed。 one of charpentier鈥檚 closest friends wasanother swiss naturalist； louis agassiz； who after some initial skepticism came to embrace；and eventually all but appropriate； the theory。
agassiz had studied under cuvier in paris and now held the post of professor of naturalhistory at the college of neuchatel in switzerland。 another friend of agassiz鈥檚； a botanistnamed karl schimper； was actually the first to coin the term ice age （in german eiszeit ）； in1837； and to propose that there was good evidence to show that ice had once lain heavilyacross not just the swiss alps； but over much of europe； asia； and north america。 it was aradical notion。 he lent agassiz his notes鈥攖hen came very much to regret it as agassizincreasingly got the credit for what schimper felt； with some legitimacy； was his theory。
charpentier likewise ended up a bitter enemy of his old friend。 alexander von humboldt； yetanother friend； may have had agassiz at least partly in mind when he observed that there arethree stages in scientific discovery： first； people deny that it is true； then they deny that it isimportant； finally they credit the wrong person。
at all events； agassiz made the field his own。 in his quest to understand the dynamics ofglaciation； he went everywhere鈥攄eep into dangerous crevasses and up to the summits of thecraggiest alpine peaks； often apparently unaware that he and his team were the first to climbthem。 nearly everywhere agassiz encountered an unyielding reluctance to accept his theories。
humboldt urged him to return to his area of real expertise； fossil fish； and give up this madobsession with ice； but agassiz was a man possessed by an idea。
agassiz鈥檚 theory found even less support in britain； where most naturalists had never seena glacier and often couldn鈥檛 grasp the crushing forces that ice in bulk exerts。 鈥渃ould scratches and polish just be due to ice ？鈥潯sked roderick murchison in a mocking tone at one meeting；evidently imagining the rocks as covered in a kind of light and glassy rime。 to his dying day；he expressed the frankest incredulity at those 鈥渋ce…mad鈥潯eologists who believed that glacierscould account for so much。 william hopkins； a cambridge professor and leading member ofthe geological society； endorsed this view； arguing that the notion that ice could transportboulders presented 鈥渟uch obvious mechanical absurdities鈥潯s to make it unworthy of thesociety鈥檚 attention。
undaunted； agassiz traveled tirelessly to promote his theory。 in 1840 he read a paper to ameeting of the british association for the advancement of science in glasgow at which hewas openly criticized by the great charles lyell。 the following year the geological society ofedinburgh passed a resolution conceding that there might be some general merit in the theorybut that certainly none of it applied to scotland。
lyell did eventually e round。 his moment of epiphany came when he realized that amoraine； or line of rocks； near his family estate in scotland； which he had passed hundreds oftimes； could only be understood if one accepted that a glacier had dropped them there。 buthaving bee converted； lyell then lost his nerve and backed off from public support of theice age idea。 it was a frustrating time for agassiz。 his marriage was breaking up； schimperwas hotly accusing him of the theft of his ideas； charpentier wouldn鈥檛 speak to him； and thegreatest living geologist offered support of only the most tepid and vacillating kind。
in 1846； agassiz traveled to america to give a series of lectures and there at last found theesteem he craved。 harvard gave him a professorship and built him a first…rate museum； themuseum of parative zoology。 doubtless it helped that he had settled in new england；where the long winters encouraged a certain sympathy for the idea of interminable periods ofcold。 it also helped that six years after his arrival the first scientific expedition to greenlandreported that nearly the whole of that semicontinent was covered in an ice sheet just like theancient one imagined in agassiz鈥檚 theory。 at long last； his ideas began to find a realfollowing。 the one central defect of agassiz鈥檚 theory was that his ice ages had no cause。 butassistance was about to e from an unlikely quarter。
in the 1860s； journals and other learned publications in britain began to receive papers onhydrostatics； electricity； and other scientific subjects from a james croll of anderson鈥檚university in glasgow。 one of the papers； on how variations in earth鈥檚 orbit might haveprecipitated ice ages； was published in the philosophical magazine in 1864 and wasrecognized at once as a work of the highest standard。 so there was some surprise； and perhapsjust a touch of embarrassment； when it turned out that croll was not an academic at theuniversity； but a janitor。
born in 1821； croll grew up poor； and his formal education lasted only to the age ofthirteen。 he worked at a variety of jobs鈥攁s a carpenter； insurance salesman； keeper of atemperance hotel鈥攂efore taking a position as a janitor at anderson鈥檚 （now the university ofstrathclyde） in glasgow。 by somehow inducing his brother to do much of his work； he wasable to pass many quiet evenings in the university library teaching himself physics；mechanics； astronomy； hydrostatics； and the other fashionable sciences of the day； andgradually began to produce a string of papers； with a particular emphasis on the motions ofearth and their effect on climate。
croll was the first to suggest that cyclical changes in the shape of earth鈥檚 orbit； fromelliptical （which is to say slightly oval） to nearly circular to elliptical again； might explain the onset and retreat of ice ages。 no one had ever thought before to consider an astronomicalexplanation for variations i