69。Farther，theairbeingvariouslyimpregnated，sometimesmoreandsometimesless，withvapoursandexhalationsfittedtoretundandintercepttheraysoflight，itfollowsthattheappearanceofthehorizontalmoonhathnotalwaysanequalfaintness，andbyconsequencethatluminary，thoughintheverysamesituation，isatonetimejudgedgreaterthanatanother。
70。Thatwehaveheregiventhetrueaccountofthephenomenaofthehorizontalmoonwill，Isuppose，befartherevidenttoanyonefromthefollowingconsiderations。First，itisplainthatwhichinthiscasesuggeststheideaofgreatermagnitudemustbesomethingwhichisitselfperceived；forthatwhichisunperceivedcannotsuggesttoourperceptionanyotherthing。Secondly，itmustbesomethingthatdoesnotconstantlyremainthesame，butissubjecttosomechangeorvariation，sincetheappearanceofthehorizontalmoonvaries，beingatonetimegreaterthanatanother。Andyet，thirdly，itcannotbethevisiblefigureormagnitude，sincethatremainsthesame，orisratherlesser，byhowmuchthemoonisnearertothehorizon。Itremainsthereforethatthetruecauseisthataffectionoralterationofthevisibleappearancewhichproceedsfromthegreaterpaucityofraysarrivingattheeye，andwhichItermfaintness：sincethisanswersalltheforementionedconditions，andIamnotconsciousofanyotherperceptionthatdoth。
71。Addtothisthatinmistyweatheritisacommonobservationthattheappearanceofthehorizontalmoonisfarlargerthanusual，whichgreatlyconspireswithandstrengthensouropinion。Neitherwoulditproveintheleastirreconcilablewithwhatwehavesaid，ifthehorizontalmoonshouldchancesometimestoseemenlargedbeyonditsusualextent，eveninmoresereneweather。Forwemustnotonlyhaveregardtothemistwhichhappenstobeintheplacewherewestand；weoughtalsototakeintoourthoughtsthewholesumofvapoursandexhalationswhichliebetwixttheeyeandthemoon：allwhichcooperatingtorendertheappearanceofthemoonmorefaint，andtherebyincreaseitsmagnitude，itmaychancetoappeargreaterthanitusuallydoes，eveninthehorizontalposition，atatimewhen，thoughtherebenoextraordinaryfogorhaziness，justintheplacewherewestand，yettheairbetweentheeyeandthemoon，takenalltogether，maybeloadedwithagreaterquantityofinterspersedvapoursandexhalationsthanatothertimes。
72。Itmaybeobjectedthatinconsequenceofourprinciplestheinterpositionofabodyinsomedegreeopaque，whichmayinterceptagreatpartoftheraysoflight，shouldrendertheappearanceofthemooninthemeridianaslargeaswhenitisviewedinthehorizon。TowhichIanswer，itisnotfaintnessanyhowappliedthatsuggestsgreatermagnitude，therebeingnonecessarybutonlyanexperimentalconnexionbetweenthosetwothings。
Itfollowsthatthefaintnesswhichenlargestheappearancemustbeappliedinsuchsort，andwithsuchcircumstances，ashavebeenobservedtoattendthevisionofgreatmagnitudes。Whenfromadistancewebeholdgreatobjects，theparticlesoftheintermediateairandvapours，whicharethemselvesunperceivable，dointerrupttheraysoflight，andtherebyrendertheappearancelessstrongandvivid：now，faintnessofappearancecausedinthissorthathbeenexperiencedtocoexistwithgreatmagnitude。Butwhenitiscausedbytheinterpositionofanopaquesensiblebody，thiscircumstancealtersthecase，sothatafaintappearancethiswaycauseddothnotsuggestgreatermagnitude，becauseithathnotbeenexperiencedtocoexistwithit。