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大学英语六级阅读理解.docx

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大学英语六级阅读理解 大学英语六级阅读理解Morerecently,somerainmakersclaimedtomakerainbyshootingguns,causingexplosions,orburningchemicals,thesmokeofwhichwassupposedtocauseraintofall.Theserainmakersaskedforasmuchas1,000dollarstomakeaninchofrain.Onewassoeffectivethathewasalmosthanged.Hewasbelievedtohavecausedatwenty-inchraininsouthernCaliforniathatfloodedtheland,killedseveralpeople,anddidmillionsofdollarsworthofdamage.Before1946,rainmakerswereeitherliarsorhonestpeoplewhohappenedtohavegoodluck.ScientificrainmakingwasstartedinthatyearbyVincentJ.Schaefer,ascientistatthelaboratoriesoftheGeneralElectricCompanyinNewYorkState.Hissuccesswastheresultofaluckyaccidentthatchangedyearsoffailureintovictory.Foralongtime,menhaveunderstoodwhereraincomesfrom.Waterfromthesurfaceofoceansandlakesbecomespartoftheair,whereitformscloudsfromwhichrainfalls.Butexactlywhatstartstheformationofraindropswasnotknownuntilquiterecently.AmannamedJohnAitkenprovedthatdropsofwatergatheraroundtinybitsofdustorothermatter.Thecentersofthedropsaresosmallthatthehumaneyecannotseethem.Withoutsuchcenters,itseems,raindropsdonotform.DuringWorldWarII,Dr.IrvingLangmuir,ascientist,washiredbytheGeneralElectricCompanytostudyhowandwhyiceformsonthewingsofairplanes.HeandayoungassistantnamedSchaeferwenttoamountaininthestateofNewHampshire,wheresnowstormsarecommonandcoldwindsblow.WhileinNewHampshire,LangmuirandSchaeferweresurprisedtolearnthatoftenthetemperatureofthecloudssurroundingthemwasfarbelowthefreezingpoint,andyeticedidnotformintheclouds.AftertheWar,Schaeferexperimentedwithamachinethatcreatedcold,moistairsimilartotheairfoundinclouds.Toimitatethemoistairofacloud,Schaeferwouldbreatheintothemachine.Thenhewoulddropintothefreezerabitofpowder,sugar,orsomeothersubstance.Forweeksandmonthshetriedeverythinghecouldimagine.Nothinghappened.Nocrystalsoficewereformed.Noneofthesubstanceswouldserveasthecenterofasnowcrystalorraindrop.OneJulymorning,Schaeferwasdroppinginbitsofvarioussubstancesandwatchingtheunsuccessfulresults.Finally,afriendsuggestedthattheyg