Людина-невидимка
Certain First Principles
Andifyouputasheetofcommonwhiteglassinwater,stillmoreifyouputitinsomedenserliquidthanwater,itwouldvanishalmostaltogether,becauselightpassingfromwatertoglassisonlyslightlyrefractedorreflectedorindeedaffectedinanyway. Itisalmostasinvisibleasajetofcoalgasorhydrogenisinair. Andforpreciselythesamereason!"
"Yes,"saidKemp,"thatisprettyplainsailing."
"Andhereisanotherfactyouwillknowtobetrue. Ifasheetofglassissmashed,Kemp,andbeatenintoapowder,itbecomesmuchmorevisiblewhileitisintheair;itbecomesatlastanopaquewhitepowder. Thisisbecausethepowderingmultipliesthesurfacesoftheglassatwhichrefractionandreflectionoccur. Inthesheetofglassthereareonlytwosurfaces;inthepowderthelightisreflectedorrefractedbyeachgrainitpassesthrough,andverylittlegetsrightthroughthepowder. Butifthewhitepowderedglassisputintowater,itforthwithvanishes. Thepowderedglassandwaterhavemuchthesamerefractiveindex;thatis,thelightundergoesverylittlerefractionorreflectioninpassingfromonetotheother.
"Youmaketheglassinvisiblebyputtingitintoaliquidofnearlythesamerefractiveindex;atransparentthingbecomesinvisibleifitisputinanymediumofalmostthesamerefractiveindex.
