Таємничий острів

           Herbertcarriedaplumb-linewhichHardinghadgivenhim,thatistosay,asimplestonefastenedtotheendofaflexiblefiber.Havingreachedaspotabouttwentyfeetfromtheedgeofthebeach,andnearlyfivehundredfeetfromthecliff,whichroseperpendicularly,Hardingthrustthepoletwofeetintothesand,andwedgingitupcarefully,hemanaged,bymeansoftheplumb-line,toerectitperpendicularlywiththeplaneofthehorizon.

           Thatdone,heretiredthenecessarydistance,when,lyingonthesand,hiseyeglancedatthesametimeatthetopofthepoleandthecrestofthecliff.Hecarefullymarkedtheplacewithalittlestick.

           ThenaddressingHerbert—"Doyouknowthefirstprinciplesofgeometry?"heasked.

           "Slightly,captain,"repliedHerbert,whodidnotwishtoputhimselfforward.

           "Yourememberwhatarethepropertiesoftwosimilartriangles?"

           "Yes,"repliedHerbert;"theirhomologoussidesareproportional."

           "Well,myboy,Ihavejustconstructedtwosimilarright-angledtriangles;thefirst,thesmallest,hasforitssidestheperpendicularpole,thedistancewhichseparatesthelittlestickfromthefootofthepoleandmyvisualrayforhypothenuse;thesecondhasforitssidestheperpendicularcliff,theheightofwhichwewishtomeasure,thedistancewhichseparatesthelittlestickfromthebottomofthecliff,andmyvisualrayalsoformsitshypothenuse,whichprovestobeprolongationofthatofthefirsttriangle."

           "Ah,captain,Iunderstand!"criedHerbert.