ABSTRACT
Itisveryeasytoshowhowimportantcontrastistounderstanding.Thearchitectinhisdrawingandthepainterinhis picturebothcasuallyintroducesomehumanfigure,togivethe onlookerapropersenseofscaleandanopportunitytocontrast thescenewithhimself.Whentheastronomersetsouttoshow uswhatourearthislike,hefindsitimportanttotalkabout otherplanets,othersunlikestars,othersolarsystems.When hetellsusthatitsdiameteris8000miles,healsotellsusthat thediameterofJupiteris86,800miles,andthisaddstoour understanding.Infactwefeelwecanunderstandfullyonly whenwecanconfidentlysay'Itmighthavebeenotherwise', andgivethedetails-whatitwouldbelikeiftheearthwere hundredsoftimesasbig,andfiveandahalftimesasfarfrom thesun;howheavythingswouldbe,howlongtheday,how coldthenight.
