meteorology-第10节

按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！




the　earth　was　warmed　by　the　sun；　and　so　air　was　generated　and　the



whole　firmament　grew；　and　the　air　caused　winds　and　solstices。　The



objection　is　that　we　always　plainly　see　the　water　that　has　been



carried　up　coming　down　again。　Even　if　the　same　amount　does　not　come



back　in　a　year　or　in　a　given　country；　yet　in　a　certain　period　all　that



has　been　carried　up　is　returned。　This　implies　that　the　celestial



bodies　do　not　feed　on　it；　and　that　we　cannot　distinguish　between



some　air　which　preserves　its　character　once　it　is　generated　and　some



other　which　is　generated　but　becomes　water　again　and　so　perishes；　on



the　contrary；　all　the　moisture　alike　is　dissolved　and　all　of　it



condensed　back　into　water。



　　The　drinkable；　sweet　water；　then；　is　light　and　is　all　of　it　drawn



up：　the　salt　water　is　heavy　and　remains　behind；　but　not　in　its　natural



place。　For　this　is　a　question　which　has　been　sufficiently　discussed　（I



mean　about　the　natural　place　that　water；　like　the　other　elements；　must



in　reason　have）；　and　the　answer　is　this。　The　place　which　we　see　the



sea　filling　is　not　its　natural　place　but　that　of　water。　It　seems　to



belong　to　the　sea　because　the　weight　of　the　salt　water　makes　it　remain



there；　while　the　sweet；　drinkable　water　which　is　light　is　carried



up。　The　same　thing　happens　in　animal　bodies。　Here；　too；　the　food



when　it　enters　the　body　is　sweet；　yet　the　residuum　and　dregs　of　liquid



food　are　found　to　be　bitter　and　salt。　This　is　because　the　sweet　and



drinkable　part　of　it　has　been　drawn　away　by　the　natural　animal　heat



and　has　passed　into　the　flesh　and　the　other　parts　of　the　body



according　to　their　several　natures。　Now　just　as　here　it　would　be　wrong



for　any　one　to　refuse　to　call　the　belly　the　place　of　liquid　food



because　that　disappears　from　it　soon；　and　to　call　it　the　place　of



the　residuum　because　this　is　seen　to　remain；　so　in　the　case　of　our



present　subject。　This　place；　we　say；　is　the　place　of　water。　Hence



all　rivers　and　all　the　water　that　is　generated　flow　into　it：　for　water



flows　into　the　deepest　place；　and　the　deepest　part　of　the　earth　is



filled　by　the　sea。　Only　all　the　light　and　sweet　part　of　it　is



quickly　carried　off　by　the　sun；　while　herest　remains　for　the　reason　we



have　explained。　It　is　quite　natural　that　some　people　should　have



been　puzzled　by　the　old　question　why　such　a　mass　of　water　leaves　no



trace　anywhere　（for　the　sea　does　not　increase　though　innumerable　and



vast　rivers　are　flowing　into　it　every　day。）　But　if　one　considers　the



matter　the　solution　is　easy。　The　same　amount　of　water　does　not　take　as



long　to　dry　up　when　it　is　spread　out　as　when　it　is　gathered　in　a　body；



and　indeed　the　difference　is　so　great　that　in　the　one　case　it　might



persist　the　whole　day　long　while　in　the　other　it　might　all　disappear



in　a　moment…as　for　instance　if　one　were　to　spread　out　a　cup　of　water



over　a　large　table。　This　is　the　case　with　the　rivers：　all　the　time



they　are　flowing　their　water　forms　a　compact　mass；　but　when　it　arrives



at　a　vast　wide　place　it　quickly　and　imperceptibly　evaporates。



　　But　the　theory　of　the　Phaedo　about　rivers　and　the　sea　is　impossible。



There　it　is　said　that　the　earth　is　pierced　by　intercommunicating



channels　and　that　the　original　head　and　source　of　all　waters　is　what



is　called　Tartarus…a　mass　of　water　about　the　centre；　from　which　all



waters；　flowing　and　standing；　are　derived。　This　primary　and　original



water　is　always　surging　to　and　fro；　and　so　it　causes　the　rivers　to



flow　on　this　side　of　the　earth's　centre　and　on　that；　for　it　has　no



fixed　seat　but　is　always　oscillating　about　the　centre。　Its　motion　up



and　down　is　what　fills　rivers。　Many　of　these　form　lakes　in　various



places　（our　sea　is　an　instance　of　one　of　these）；　but　all　of　them



come　round　again　in　a　circle　to　the　original　source　of　their　flow；



many　at　the　same　point；　but　some　at　a　point　opposite　to　that　from



which　they　issued；　for　instance；　if　they　started　from　the　other　side



of　the　earth's　centre；　they　might　return　from　this　side　of　it。　They



descend　only　as　far　as　the　centre；　for　after　that　all　motion　is



upwards。　Water　gets　its　tastes　and　colours　from　the　kind　of　earth



the　rivers　happened　to　flow　through。



　　But　on　this　theory　rivers　do　not　always　flow　in　the　same　sense。



For　since　they　flow　to　the　centre　from　which　they　issue　forth　they



will　not　be　flowing　down　any　more　than　up；　but　in　whatever　direction



the　surging　of　Tartarus　inclines　to。　But　at　this　rate　we　shall　get　the



proverbial　rivers　flowing　upwards；　which　is　impossible。　Again；　where



is　the　water　that　is　generated　and　what　goes　up　again　as　vapour　to



come　from？　For　this　must　all　of　it　simply　be　ignored；　since　the



quantity　of　water　is　always　the　same　and　all　the　water　that　flows



out　from　the　original　source　flows　back　to　it　again。　This　itself　is



not　true；　since　all　rivers　are　seen　to　end　in　the　sea　except　where　one



flows　into　another。　Not　one　of　them　ends　in　the　earth；　but　even　when



one　is　swallowed　up　it　comes　to　the　surface　again。　And　those　rivers



are　large　which　flow　for　a　long　distance　through　a　lowying　country；



for　by　their　situation　and　length　they　cut　off　the　course　of　many



others　and　swallow　them　up。　This　is　why　the　Istrus　and　the　Nile　are



the　greatest　of　the　rivers　which　flow　into　our　sea。　Indeed；　so　many



rivers　fall　into　them　that　there　is　disagreement　as　to　the　sources



of　them　both。　All　of　which　is　plainly　impossible　on　the　theory；　and



the　more　so　as　it　derives　the　sea　from　Tartarus。



　　Enough　has　been　said　to　prove　that　this　is　the　natural　place　of



water　and　not　of　the　sea；　and　to　explain　why　sweet　water　is　only　found



in　rivers；　while　salt　water　is　stationary；　and　to　show　that　the　sea　is



the　end　rather　than　the　source　of　water；　analogous　to　the　residual



matter　of　all　food；　and　especially　liquid　food；　in　animal　bodies。







　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　3







　　We　must　now　explain　why　the　sea　is　salt；　and　ask　whether　it



eternally　exists　as　identically　the　same　body；　or　whether　it　did　not



exist　at　all　once　and　some　day　will　exist　no　longer；　but　will　dry　up



as　some　people　think。



　　Every　one　admits　this；　that　if　the　whole　world　originated　the　sea



did　too；　for　they　make　them　come　into　being　at　the　same　time。　It



follows　that　if　the　universe　is　eternal　the　same　must　be　true　of　the



sea。　Any　one　who　thinks　like　Democritus　that　the　sea　is　diminishing



and　will　disappear　in　the　end　reminds　us　of　Aesop's　tales。　His　story



was　that　Charybdis　had　twice　sucked　in　the　sea：　the　first　time　she



made　the　mountains　visible；　the　second　time　the　islands；　and　when



she　sucks　it　in　for　the　last　time　she　will　dry　it　up　entirely。　Such



a　tale　is　appropriate　enough　to　Aesop　in　a　rage　with　the　ferryman；　but



not　to　serious　inquirers。　Whatever　made　the　sea　remain　at　first；



whether　it　was　its　weight；　as　some　even　of　those　who　hold　these



views　say　（for　it　is　easy　to　see　the　cause　here）；　or　some　other



reason…clearly　the　same　thing　must　make　it　persist　for　ever。　They　must



either　deny　that　the　water　raised　by　the　sun　will　return　at　all；　or；



if　it　does；　they　must　admit　that　the　sea　persists　for　ever　or　as



long　as　this　process　goes　on；　and　again；　that　for　the　same　period　of



time　that　sweet　water　must　have　been　carried　up　beforehand。　So　the　sea



will　never　dry　up：　for　before　that　can　happen　the　water　that　has



gone　up　beforehand　will　return　to　it：　for　if　you　say　that　this　happens



once　you　must　admit　its　recurrence。　If　you　stop　the　sun's　course　there



is　no　drying　agency。　If　you　let　it　go　on　it　will　draw　up　the　sweet



water　as　we　have　said　whenever　it　approaches；　and　let　it　descend　again



when　it　recedes。　This　notion　about　the　sea　is　derived　from　the　fact



that　many　places　are　found　to　be　drier　now　than　they　once　were。　Why



this　is　so　we　have　explained。　The　phenomenon　is　due　to　temporary



excess　of　rain　and　not　to　any　process　of　becoming　in　which　the



universe　or　its　parts　are　involved。　Some　day　the　opposite　will　take



place　and　after　that　the　earth　will　grow　dry　once　again。　We　must



recognize　that　this　process　always　goes　on　thus　in　a　cycle；　for　that



is　more　satisfactory　than　to　suppose　a　change　in　the　whole　world　in



order　to　explain　these　facts。　But　we　have　dwelt　longer　on　this　point



than　it　deserves。



　　To　return　to　the　saltness　of　the　sea：　those　who　create　the　sea



once　for　all；　or　indeed　generate　it　at　all；　cannot　account　for　its



saltness。　It　makes　no　difference　whether　the　sea　is　the　residue　of　all



the　moisture　that　is　about　the　earth　and　has　been　drawn　up　by　the　sun；



or　whether　all　the　flavour　existing　in　the　whole　mass　of　sweet　water



is　due　to　the　admixture　of　a　certain　kind　of　earth。　Since　the　total



volume　of　the　sea　is　the　same　once　the　water　that　evaporated　has



returned；　it　follows　that　it　must　either　have　been　salt　at　first



to