on the heavens-第23部分

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　needle；　for　instance…sink　down；　and　sometimes　a　thing　floats　because　it　is　small；　as　with　gold　dust　and　the　various　earthy　and　dusty　materials　which　throng　the　air。　With　regard　to　these　questions；　it　is　wrong　to　accept　the　explanation　offered　by　Democritus。　He　says　that　the　warm　bodies　moving　up　out　of　the　water　hold　up　heavy　bodies　which　are　broad；　while　the　narrow　ones　fall　through；　because　the　bodies　which　offer　this　resistance　are　not　numerous。　But　this　would　be　even　more　likely　to　happen　in　air…an　objection　which　he　himself　raises。　His　reply　to　the　objection　is　feeble。　In　the　air；　he　says；　the　'drive'　（meaning　by　drive　the　movement　of　the　upward　moving　bodies）　is　not　uniform　in　direction。　But　since　some　continua　are　easily　divided　and　others　less　easily；　and　things　which　produce　division　differ　similarly　in　the　case　with　which　they　produce　it；　the　explanation　must　be　found　in　this　fact。　It　is　the　easily　bounded；　in　proportion　as　it　is　easily　bounded；　which　is　easily　divided；　and　air　is　more　so　than　water；　water　than　earth。　Further；　the　smaller　the　quantity　in　each　kind；　the　more　easily　it　is　divided　and　disrupted。　Thus　the　reason　why　broad　things　keep　their　place　is　because　they　cover　so　wide　a　surface　and　the　greater　quantity　is　less　easily　disrupted。　Bodies　of　the　opposite　shape　sink　down　because　they　occupy　so　little　of　the　surface；　which　is　therefore　easily　parted。　And　these　considerations　apply　with　far　greater　force　to　air；　since　it　is　so　much　more　easily　divided　than　water。　But　since　there　are　two　factors；　the　force　responsible　for　the　downward　motion　of　the　heavy　body　and　the　disruption…resisting　force　of　the　continuous　surface；　there　must　be　some　ratio　between　the　two。　For　in　proportion　as　the　force　applied　by　the　heavy　thing　towards　disruption　and　division　exceeds　that　which　resides　in　the　continuum；　the　quicker　will　it　force　its　way　down；　only　if　the　force　of　the　heavy　thing　is　the　weaker；　will　it　ride　upon　the　surface。　　　We　have　now　finished　our　examination　of　the　heavy　and　the　light　and　of　the　phenomena　connected　with　them。


　　　　　　　　　　　　　　　　　　　　　　　　　　　　THE　END　。