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1、·3 BeesandColour Onourtableinthegardenweputabluecard,andallaroundthisbluecardweputanumberofdifferentgreycards.Thesegreycardsareofallpossibleshadesofgreyandincludewhiteandblack.Oneachcardawatch—glassisplaced.Thewatch—glassonthebluecardhassomesyrup(果汁)init,alltheothersareempty.Afterashorttim
2、ebeesfindthesyrup,andtheycomeforitagainandagain.Then,aftersomehours,wetakeawaythewatch—glassofsyrupwhichwasonthebluecardandputanemptyoneinitsplace. Nowwhatdothebeesdo?Theystillgostraighttothebluecard,althoughthereisnosyrupthere.Theydonotgotoanyofthegreycards,inspiteofthefactthatoneofthegrey
3、cardsisofexactlythesamebrightnessasthebluecard.Thusthebeesdonotmistakeanyshadeofgreyforblue.Inthiswaywehaveprovedthattheydoreallyseeblueasacolour. Wecanfindoutinjustthesamewaywhatothercoloursbeescansee.Itturnsoutthatbeescanseevariouscolours,buttheseinsectsdifferfromusasregardstheircolour—s
4、enseintwoveryinterestingways.Supposewetrainbeestocometoaredcard,and,havingdoneso,weputtheredcardonthetableinthegardenamongthesetofdifferentgreycards.Thistimewefindthatthebeesmistakeredfordarkgreyorblack.Theycannotdistinguishbetweenthem.Thismeansthatredisnotacolouratallforbees;forthemitisjustdark
5、greyorback. Thatisonestrangefact;hereisanother.Arainbowisredononeedge,violetontheother.Outsidethevioletoftherainbowthereisanothercolourwhichwecannotseeatall.Thiscolourbeyondtheviolet,invisibletous,iscalledtheultraviolet.Althoughitisinvisible,weknowthattheultra—violetistherebecauseitaffects
6、aphotographicplate.Now,althoughweareunabletoseeultra—violetlight,beescandoso;forthemultra—violetisacolour.Thusbeesseeacolourwhichwecannotevenimagine.Thishasbeenfoundoutbytrainingbeestocomeforsyruptovariouspartsofaspectrum,orartificialrainbow,thrownbyaprismonatableinadarkroom.Insuchanexperimentth
7、einsectscanbetaughttoflytotheultra—violet,whichforusisjustdarkness.16. Theexperimentwithbeesdescribedinthefirstandsecondparagraphstellusthatbeesregardblueasacolour.17. Thethirdparagraphtellsusthatbeesalsoregardredasacolour.1
