“Thenextpointtoberegardedwasamatteroffargreaterimportance。Fromindicationsaffordedbythebarometer，wefindthat，inascensionsfromthesurfaceoftheearthwehave，attheheightof1，000feet，leftbelowusaboutone-thirtiethoftheentiremassofatmosphericair，thatat10，600wehaveascendedthroughnearlyone-third；andthatat18，000，whichisnotfarfromtheelevationofCotopaxi，wehavesurmountedone-halfthematerial，or，atallevents，one-halftheponderable，bodyofairincumbentuponourglobe。Itisalsocalculatedthatatanaltitudenotexceedingthehundredthpartoftheearth’sdiameterthatis，notexceedingeightymilestherarefactionwouldbesoexcessivethatanimallifecouldinnomannerbesustained，and，moreover，thatthemostdelicatemeanswepossessofascertainingthepresenceoftheatmospherewouldbeinadequatetoassureusofitsexistence。ButI
didnotfailtoperceivethattheselattercalculationsarefoundedaltogetheronourexperimentalknowledgeofthepropertiesofair，andthemechanicallawsregulatingitsdilationandcompression，inwhatmaybecalled，comparativelyspeaking，theimmediatevicinityoftheearthitself；and，atthesametime，itistakenforgrantedthatanimallifeisandmustbeessentiallyincapableofmodificationatanygivenunattainabledistancefromthesurface。Now，allsuchreasoningandfromsuchdatamust，ofcourse，besimplyanalogical。
Thegreatestheighteverreachedbymanwasthatof25，000feet，attainedintheaeronauticexpeditionofMessieursGay-LussacandBiot。Thisisamoderatealtitude，evenwhencomparedwiththeeightymilesinquestion；andIcouldnothelpthinkingthatthesubjectadmittedroomfordoubtandgreatlatitudeforspeculation。
“But，inpointoffact，anascensionbeingmadetoanygivenaltitude，theponderablequantityofairsurmountedinanyfartherascensionisbynomeansinproportiontotheadditionalheightascendedasmaybeplainlyseenfromwhathasbeenstatedbefore，butinaratioconstantlydecreasing。Itisthereforeevidentthat，ascendashighaswemay，wecannot，literallyspeaking，arriveatalimitbeyondwhichnoatmosphereistobefound。Itmustexist，I
argued；althoughitmayexistinastateofinfiniterarefaction。