m…just　as　the　movement　of　coming　to　health　does　not　take　any　direction　which　chance　or　the　wishes　of　the　mover　may　select。　Thus；　too；　fire　and　earth　move　not　to　infinity　but　to　opposite　points；　and　since　the　opposition　in　place　is　between　above　and　below；　these　will　be　the　limits　of　their　movement。　（Even　in　circular　movement　there　is　a　sort　of　opposition　between　the　ends　of　the　diameter；　though　the　movement　as　a　whole　has　no　contrary：　so　that　here　too　the　movement　has　in　a　sense　an　opposed　and　finite　goal。）　There　must　therefore　be　some　end　to　locomotion：　it　cannot　continue　to　infinity。　　　This　conclusion　that　local　movement　is　not　continued　to　infinity　is　corroborated　by　the　fact　that　earth　moves　more　quickly　the　nearer　it　is　to　the　centre；　and　fire　the　nearer　it　is　to　the　upper　place。　But　if　movement　were　infinite　speed　would　be　infinite　also；　and　if　speed　then　weight　and　lightness。　For　as　superior　speed　in　downward　movement　implies　superior　weight；　so　infinite　increase　of　weight　necessitates　infinite　increase　of　speed。　　　Further；　it　is　not　the　action　of　another　body　that　makes　one　of　these　bodies　move　up　and　the　other　down；　nor　is　it　constraint；　like　the　'extrusion'　of　some　writers。　For　in　that　case　the　larger　the　mass　of　fire　or　earth　the　slower　would　be　the　upward　or　downward　movement；　but　the　fact　is　the　reverse：　the　greater　the　mass　of　fire　or　earth　the　quicker　always　is　its　movement　towards　its　own　place。　Again；　the　speed　of　the　movement　would　not　increase　towards　the　end　if　it　were　due　to　constraint　or　extrusion；　for　a　constrained　movement　always　diminishes　in　speed　as　the　source　of　constraint　becomes　more　distant；　and　a　body　moves　without　constraint　to　the　place　whence　it　was　moved　by　constraint。　　　A　consideration　of　these　points；　then；　gives　adequate　assurance　of　the　truth　of　our　contentions。　The　same　could　also　be　shown　with　the　aid　of　the　discussions　which　fall　under　First　Philosophy；　as　well　as　from　the　nature　of　the　circular　movement；　which　must　be　eternal　both　here　and　in　the　other　worlds。　It　is　plain；　too；　from　the　following　considerations　that　the　universe　must　be　one。　　　The　bodily　elements　are　three；　and　therefore　the　places　of　the　elements　will　be　three　also；　the　place；　first；　of　the　body　which　sinks　to　the　bottom；　namely　the　region　about　the　centre；　the　place；　secondly；　of　the　revolving　body；　namely　the　outermost　place；　and　thirdly；　the　intermediate　place；　belonging　to　the　intermediate　body。　Here　in　this　third　place　will　be　the　body　which　rises　to　the　surface；　since；　if　not　here；　it　will　be　elsewhere；　and　it　cannot　be　elsewhere：　for　we　have　two　bodies；　one　weightless；　one　endowed　with　weight；　and　below　is　place　of　the　body　endowed　with　weight；　since　the　region　about　the　centre　has　been　given　to　the　heavy　body。　And　its　position　cannot　be　unnatural　to　it；　for　it　would　have　to　be　natural　to　something　else；　and　there　is　nothing　else。　It　must　then　occupy　the　intermediate　place。　What　distinctions　there　are　within　the　intermediate　itself　we　will　explain　later　on。　　　We　have　now　said　enough　to　make　plain　the　character　and　number　of　the　bodily　elements；　the　place　of　each；　and　further；　in　general；　how　many　in　number　the　various　places　are。
  9
  We　must　show　not　only　that　the　heaven　is　one；　but　also　that　more　than　one　heaven　is　and；　further；　that；　as　exempt　from　decay　and　generation；　the　heaven　is　eternal。　We　may　begin　by　raising　a　difficulty。　From　one　point　of　view　it　might　seem　impossible　that　the　heaven　should　be　one　and　unique；　since　in　all　formations　and　products　whether　of　nature　or　of　art　we　can　distinguish　the　shape　in　itself　and　the　shape　in　combination　with　matter。　For　instance　the　form　of　the　sphere　is　one　thing　and　the　gold　or　bronze　sphere　another；　the　shape　of　the　circle　again　is　one　thing；　the　bronze　or　wooden　circle　another。　For　when　we　state　the　essential　nature　of　the　sphere　or　circle　we　do　not　include　in　the　formula　gold　or　bronze；　because　they　do　not　belong　to　the　essence；　but　if　we　are　speaking　of　the　copper　or　gold　sphere　we　do　include　them。　We　still　make　the　distinction　even　if　we　cannot　conceive　or　apprehend　any　other　example　beside　the　particular　thing。　This　may；　of　course；　sometimes　be　the　case：　it　might　be；　for　instance；　that　only　one　circle　could　be　found；　yet　none　the　less　the　difference　will　remain　between　the　being　of　circle　and　of　this　particular　circle；　the　one　being　form；　the　other　form　in　matter；　i。e。　a　particular　thing。　Now　since　the　universe　is　perceptible　it　must　be　regarded　as　a　particular；　for　everything　that　is　perceptible　subsists；　as　we　know；　in　matter。　But　if　it　is　a　particular；　there　will　be　a　distinction　between　the　being　of　'this　universe'　and　of　'universe'　unqualified。　There　is　a　difference；　then；　between　'this　universe'　and　simple　'universe'；　the　second　is　form　and　shape；　the　first　form　in　combination　with　matter；　and　any　shape　or　form　has；　or　may　have；　more　than　one　particular　instance。　　　On　the　supposition　of　Forms　such　as　some　assert；　this　must　be　the　case；　and　equally　on　the　view　that　no　such　entity　has　a　separate　existence。　For　in　every　case　in　which　the　essence　is　in　matter　it　is　a　fact　of　observation　that　the　particulars　of　like　form　are　several　or　infinite　in　number。　Hence　there　either　are；　or　may　be；　more　heavens　than　one。　On　these　grounds；　then；　it　might　be　inferred　either　that　there　are　or　that　there　might　be　several　heavens。　We　must；　however；　return　and　ask　how　much　of　this　argument　is　correct　and　how　much　not。　　　Now　it　is　quite　right　to　say　that　the　formula　of　the　shape　apart　from　the　matter　must　be　different　from　that　of　the　shape　in　the　matter；　and　we　may　allow　this　to　be　true。　We　are　not；　however；　therefore　compelled　to　assert　a　plurality　of　worlds。　Such　a　plurality　is　in　fact　impossible　if　this　world　contains　the　entirety　of　matter；　as　in　fact　it　does。　But　perhaps　our　contention　can　be　made　clearer　in　this　way。　Suppose　'aquilinity'　to　be　curvature　in　the　nose　or　flesh；　and　flesh　to　be　the　matter　of　aquilinity。　Suppose　further；　that　all　flesh　came　together　into　a　single　whole　of　flesh　endowed　with　this　aquiline　quality。　Then　neither　would　there　be；　nor　could　there　arise；　any　other　thing　that　was　aquiline。　Similarly；　suppose　flesh　and　bones　to　be　the　matter　of　man；　and　suppose　a　man　to　be　created　of　all　flesh　and　all　bones　in　indissoluble　union。　The　possibility　of　another　man　would　be　removed。　Whatever　case　you　took　it　would　be　the　same。　The　general　rule　is　this：　a　thing　whose　essence　resides　in　a　substratum　of　matter　can　never　come　into　being　in　the　absence　of　all　matter。　Now　the　universe　is　certainly　a　particular　and　a　material　thing：　if　however；　it　is　composed　not　of　a　part　but　of　the　whole　of　matter；　then　though　the　being　of　'universe'　and　of　'this　universe'　are　still　distinct；　yet　there　is　no　other　universe；　and　no　possibility　of　others　being　made；　because　all　the　matter　is　already　included　in　this。　It　remains；　then；　only　to　prove　that　it　is　composed　of　all　natural　perceptible　body。　　　First；　however；　we　must　explain　what　we　mean　by　'heaven'　and　in　how　many　senses　we　use　the　word；　in　order　to　make　clearer　the　object　of　our　inquiry。　（a）　In　one　sense；　then；　we　call　'heaven'　the　substance　of　the　extreme　circumference　of　the　whole；　or　that　natural　body　whose　place　is　at　the　extreme　circumference。　We　recognize　habitually　a　special　right　to　the　name　'heaven'　in　the　extremity　or　upper　region；　which　we　take　to　be　the　seat　of　all　that　is　divine。　（b）　In　another　sense；　we　use　this　name　for　the　body　continuous　with　the　extreme　circumference　which　contains　the　moon；　the　sun；　and　some　of　the　stars；　these　we　say　are　'in　the　heaven'。　（c）　In　yet　another　sense　we　give　the　name　to　all　body　included　within　extreme　circumference；　since　we　habitually　call　the　whole　or　totality　'the　heaven'。　The　word；　then；　is　used　in　three　senses。　　　Now　the　whole　included　within　the　extreme　circumference　must　be　composed　of　all　physical　and　sensible　body；　because　there　neither　is；　nor　can　come　into　being；　any　body　outside　the　heaven。　For　if　there　is　a　natural　body　outside　the　extreme　circumference　it　must　be　either　a　simple　or　a　composite　body；　and　its　position　must　be　either　natural　or　unnatural。　But　it　cannot　be　any　of　the　simple　bodies。　For；　first；　it　has　been　shown　that　that　which　moves　in　a　circle　cannot　change　its　place。　And；　secondly；　it　cannot　be　that　which　moves　from　the　centre　or　that　which　lies　lowest。　Naturally　they　could　not　be　there；　since　their　proper　places　are　elsewhere；　and　if　these　are　there　unnaturally；　the　exterior　place　will　be　natural　to　some　other　body；　since　a　place　which　is　unnatural　to　one　body　must　be　natural　to　another：　but　we　saw　that　there　is　no　other　body　besides　these。　Then　it　is　not　possible　that　any　simple　body　should　be　outside　the　heaven。　But；　if　no　simple　body；　neither　can　any　mixed　body　be　there：　for　the　presence　of　the　simple　body　is　involved　in　the　presence　of　the　mixture。　Further　neither　can　any　body　come　into　that　place：　for　it　will　do　so　either　naturally　or　unnaturally；　and　will　be　either　simple　or　composite；　so　that　the　same　argument　will　apply；　since　it　makes　no　difference　whether　the　question　is　'does　A　exist？'　or　'could　A　come　to　exist？'　From　our　arguments　then　it　is　evident　not　only　that　there　is　not；　but　also　that　th