Theideaofrainmakingisalmostasoldasman,butitwasnotuntil1946thatmansucceededinmakingrain.Inancienttimes,rainmakershadclaimedtobringrainbymanymethods:dancing,singing,killingvariouskindsoflivingcreatures(includinghumans),andblowingastreamofwaterintotheairfromakindofpipe.
Morerecently,somerainmakersclaimedtomakerainbyshootingguns,causingexplosions,orburningchemicals,thesmokeofwhichwassupposedtocauseraintofall.Theserainmakersaskedforasmuchas1,000dollarstomakeaninchofrain.Onewassoeffectivethathewasalmosthanged.Hewasbelievedtohavecausedatwenty-inchraininsouthernCaliforniathatfloodedtheland,killedseveralpeople,anddidmillionsofdollars'worthofdamage.
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,afriendsuggestedthattheygotoeatlunch,andSchaefergladlywentwithhim.Asusual,heleftthecoverofthefreezerup,sincecoldairsinksandwouldnotescapefromthebox.
Returningfromlunch,Schaeferwasbeginningtoperformhisexperimentsagainwhenhehappenedtolookatthetemperatureofthefreezer.Ithadrisentoapointhigherthanthatrequiredforicecrystalstoremainsolid.Thewarmsummerweatherhadarrivedwithouthisnoticingit.Hewouldhavetobemorecarefulinthefuture.
Thereweretwochoicesnow.Hecouldclosethecoverandwaitforthefreezeritselftolowertheairtemperature,orhecouldmaketheprocessoccurfasterbyaddingdryice,agasinsolidformthatisvery,verycold.Hechosethelatterplan.Hedecidedtotryacontainerofdryice.
Ashedroppedthesteamingwhitedryiceintothefreezer,hehappenedtobreatheoutalargeamountofair.Andthere,beforehiseyes,ithappened!Hehadmadeicecrystals,notbyaddingcenterstothemoisturebutbycoolingthebreathsomuchthattheliquidhadtoformcrystals!Schaefercalledtohishelperstocomeandwatch.Thenhebegantoblowhisbreathintothefreezeranddroplargepiecesofdryicethroughittocreatecrystalswhichbecameatinysnowstormfallingslowlytothefloorofhislaboratory.
Ifhecouldmakesnowinafreezer,Schaeferthought,whycouldn'thedosoinarealcloud?Hedecidedtotryitinanairplanewithamachinetoblowdryiceoutintotheclouds.
OnacolddayinNovember,SchaeferandLangmuirsawcloudsinthesky,andSchaeferclimbedintotheairplane.Herealizedhewouldhavetoflysomedistancebeforefindingtherightkindofcloud—abiggrayonethatmustbefilledwithmoisture.Seeingone,Schaefertoldthepilotoftheplanetoflyabovethecloud.Atthepropertime,hestartedthemachine,anddryicebegantofallfromtheairplaneintothecloudbelow.Whenhalftheloadofdryicewasgone,themotorstoppedbecauseithadbecometoocold.Schaeferhadtothinkquickly.Hemerelythrewtheremainingdryiceoutofthewindowoftheplaneandintothecloudbelow.
Ontheground,Dr.Langmuirwatchedexcitedlyandsawsnowfallingfromthebottomofthecloud.WhenSchaeferreturnedtotheground,bluewithcold,Langmuirrantohim,shouting,"Youhavemadehistory!"Andindeedhehad.AlmostassoonasthenewsofhisaccomplishmentwassentacrosstheUnitedStatesandaroundtheworld,ahundredotherrainmakerswerethrowingdryiceintoclouds—or"seedingtheclouds"asitwascalled.
WhenSchaeferdiscoveredthaticecrystalscouldbeformedwithoutfindingtherightmaterialtomakecentersforthecrystals,hestoppedsearchingforsuchmaterials.ButanotheryoungworkeratGeneralElectric,BernardVonnegutbeganlookingthroughachemistrybookforsomechemicalcompoundthatmighthavetherightsizeandshapetoformcrystalsaroundit.Hefoundwhathewasbookingfor.Itwasacompoundcalledsilveriodide(碘化银).Hegotsomesilveriodideanddevelopedawayofburningittoproducetinyparticlesthatwouldseparateintheairandformsnow—hehoped.
Finallyheshotthematerialupintotheairandwaitedforthestorm.Nothinghappened.Hecouldn'tunderstandwhy.Thecompoundoughttoformentersforcrystals.Heaskedascientisttoexaminethechemicalshehadused.Therewasthetrouble.Thesilveriodidehehadusedwasnotpure.
Hegotmoreofthematerial,performedhisexperimentagain,andtherewerethesnowcrystals!Today,scientificrainmakersgenerallyusesilveriodide,Whichcanbesentintotheairfromthegroundbymeansofasimple,inexpensivemachine.Thisprocessismoresatisfactorythantheuseofdryicewhichcanbedestructive.
1.Humanbeingswereabletomakeraininancienttimes.
2.Dr.IrvingLangmuirandSchaeferwenttoNewHampshiretostudyhowandwhyiceformsonthewingsofairplanes.
3.Schaeferfoundouttheraindropscouldbemadewithouthavingtosearchtherightmaterialtomaketheircenters.
4.Usingsilveriodidetomakerainismoresatisfactorythanusingdryice.
5.Raincanbemadebyshootingsaltontotheclouds.
6.Schaeferfoundthewarmsummerweatherwasfavorableforrainmaking.
7.BernardVonnegutlookedthroughachemistrybooktofindwhethersilveriodidewastherightmaterialformakingrain.8.Schaefersucceededinmakingicecrystalsbycoolingthebreathsomuchthattheliquid
9.InNewHampshireSchaeferexperimentedwithamachinecreatingcold,moistair
similartotheairorothermatter.
10.AccordingtoJohnAitken,waterdropsgatheraround__
答案：1.N2.Y3.Y4.Y5.NG6.N7.N8.hadtoform9.foundintheclouds10.tinybitsofdust
