meteorology-第6章

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is　continually　forming　in　it　too。



　　Again；　even　in　the　case　of　the　water　that　is　not　being　formed　from



day　to　day　but　exists　as　such；　we　must　not　suppose　as　some　do　that



rivers　have　their　source　in　definite　subterranean　lakes。　On　the



contrary；　just　as　above　the　earth　small　drops　form　and　these　join



others；　till　finally　the　water　descends　in　a　body　as　rain；　so　too　we



must　suppose　that　in　the　earth　the　water　at　first　trickles　together



little　by　little；　and　that　the　sources　of　the　rivers　drip；　as　it　were；



out　of　the　earth　and　then　unite。　This　is　proved　by　facts。　When　men



construct　an　aqueduct　they　collect　the　water　in　pipes　and　trenches；　as



if　the　earth　in　the　higher　ground　were　sweating　the　water　out。



Hence；　too；　the　head…waters　of　rivers　are　found　to　flow　from



mountains；　and　from　the　greatest　mountains　there　flow　the　most



numerous　and　greatest　rivers。　Again；　most　springs　are　in　the



neighbourhood　of　mountains　and　of　high　ground；　whereas　if　we　except



rivers；　water　rarely　appears　in　the　plains。　For　mountains　and　high



ground；　suspended　over　the　country　like　a　saturated　sponge；　make　the



water　ooze　out　and　trickle　together　in　minute　quantities　but　in　many



places。　They　receive　a　great　deal　of　water　falling　as　rain　（for　it



makes　no　difference　whether　a　spongy　receptacle　is　concave　and



turned　up　or　convex　and　turned　down：　in　either　case　it　will　contain



the　same　volume　of　matter）　and；　they　also　cool　the　vapour　that　rises



and　condense　it　back　into　water。



　　Hence；　as　we　said；　we　find　that　the　greatest　rivers　flow　from　the



greatest　mountains。　This　can　be　seen　by　looking　at　itineraries：　what



is　recorded　in　them　consists　either　of　things　which　the　writer　has



seen　himself　or　of　such　as　he　has　compiled　after　inquiry　from　those



who　have　seen　them。



　　In　Asia　we　find　that　the　most　numerous　and　greatest　rivers　flow　from



the　mountain　called　Parnassus；　admittedly　the　greatest　of　all



mountains　towards　the　south…east。　When　you　have　crossed　it　you　see　the



outer　ocean；　the　further　limit　of　which　is　unknown　to　the　dwellers



in　our　world。　Besides　other　rivers　there　flow　from　it　the　Bactrus；　the



Choaspes；　the　Araxes：　from　the　last　a　branch　separates　off　and　flows



into　lake　Maeotis　as　the　Tanais。　From　it；　too；　flows　the　Indus；　the



volume　of　whose　stream　is　greatest　of　all　rivers。　From　the　Caucasus



flows　the　Phasis；　and　very　many　other　great　rivers　besides。　Now　the



Caucasus　is　the　greatest　of　the　mountains　that　lie　to　the　northeast；



both　as　regards　its　extent　and　its　height。　A　proof　of　its　height　is



the　fact　that　it　can　be　seen　from　the　so…called　'deeps'　and　from　the



entrance　to　the　lake。　Again；　the　sun　shines　on　its　peaks　for　a　third



part　of　the　night　before　sunrise　and　again　after　sunset。　Its　extent　is



proved　by　the　fact　that　thought　contains　many　inhabitable　regions



which　are　occupied　by　many　nations　and　in　which　there　are　said　to　be



great　lakes；　yet　they　say　that　all　these　regions　are　visible　up　to　the



last　peak。　From　Pyrene　（this　is　a　mountain　towards　the　west　in



Celtice）　there　flow　the　Istrus　and　the　Tartessus。　The　latter　flows



outside　the　pillars；　while　the　Istrus　flows　through　all　Europe　into



the　Euxine。　Most　of　the　remaining　rivers　flow　northwards　from　the



Hercynian　mountains；　which　are　the　greatest　in　height　and　extent　about



that　region。　In　the　extreme　north；　beyond　furthest　Scythia；　are　the



mountains　called　Rhipae。　The　stories　about　their　size　are　altogether



too　fabulous：　however；　they　say　that　the　most　and　（after　the　Istrus）



the　greatest　rivers　flow　from　them。　So；　too；　in　Libya　there　flow



from　the　Aethiopian　mountains　the　Aegon　and　the　Nyses；　and　from　the



so…called　Silver　Mountain　the　two　greatest　of　named　rivers；　the



river　called　Chremetes　that　flows　into　the　outer　ocean；　and　the　main



source　of　the　Nile。　Of　the　rivers　in　the　Greek　world；　the　Achelous



flows　from　Pindus；　the　Inachus　from　the　same　mountain；　the　Strymon；



the　Nestus；　and　the　Hebrus　all　three　from　Scombrus；　many　rivers；



too；　flow　from　Rhodope。



　　All　other　rivers　would　be　found　to　flow　in　the　same　way；　but　we　have



mentioned　these　as　examples。　Even　where　rivers　flow　from　marshes；



the　marshes　in　almost　every　case　are　found　to　lie　below　mountains　or



gradually　rising　ground。



　　It　is　clear　then　that　we　must　not　suppose　rivers　to　originate　from



definite　reservoirs：　for　the　whole　earth；　we　might　almost　say；　would



not　be　sufficient　（any　more　than　the　region　of　the　clouds　would　be）　if



we　were　to　suppose　that　they　were　fed　by　actually　existing　water



only　and　it　were　not　the　case　that　as　some　water　passed　out　of



existence　some　more　came　into　existence；　but　rivers　always　drew



their　stream　from　an　existing　store。　Secondly；　the　fact　that　rivers



rise　at　the　foot　of　mountains　proves　that　a　place　transmits　the



water　it　contains　by　gradual　percolation　of　many　drops；　little　by



little；　and　that　this　is　how　the　sources　of　rivers　originate。　However；



there　is　nothing　impossible　about　the　existence　of　such　places



containing　a　quantity　of　water　like　lakes：　only　they　cannot　be　big



enough　to　produce　the　supposed　effect。　To　think　that　they　are　is



just　as　absurd　as　if　one　were　to　suppose　that　rivers　drew　all　their



water　from　the　sources　we　see　（for　most　rivers　do　flow　from



springs）。　So　it　is　no　more　reasonable　to　suppose　those　lakes　to



contain　the　whole　volume　of　water　than　these　springs。



　　That　there　exist　such　chasms　and　cavities　in　the　earth　we　are　taught



by　the　rivers　that　are　swallowed　up。　They　are　found　in　many　parts　of



the　earth：　in　the　Peloponnesus；　for　instance；　there　are　many　such



rivers　in　Arcadia。　The　reason　is　that　Arcadia　is　mountainous　and　there



are　no　channels　from　its　valleys　to　the　sea。　So　these　places　get



full　of　water；　and　this；　having　no　outlet；　under　the　pressure　of　the



water　that　is　added　above；　finds　a　way　out　for　itself　underground。



In　Greece　this　kind　of　thing　happens　on　quite　a　small　scale；　but　the



lake　at　the　foot　of　the　Caucasus；　which　the　inhabitants　of　these　parts



call　a　sea；　is　considerable。　Many　great　rivers　fall　into　it　and　it　has



no　visible　outlet　but　issues　below　the　earth　off　the　land　of　the



Coraxi　about　the　so…called　'deeps　of　Pontus'。　This　is　a　place　of



unfathomable　depth　in　the　sea：　at　any　rate　no　one　has　yet　been　able　to



find　bottom　there　by　sounding。　At　this　spot；　about　three　hundred



stadia　from　land；　there　comes　up　sweet　water　over　a　large　area；　not



all　of　it　together　but　in　three　places。　And　in　Liguria　a　river　equal



in　size　to　the　Rhodanus　is　swallowed　up　and　appears　again　elsewhere：



the　Rhodanus　being　a　navigable　river。







　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　14







　　The　same　parts　of　the　earth　are　not　always　moist　or　dry；　but　they



change　according　as　rivers　come　into　existence　and　dry　up。　And　so



the　relation　of　land　to　sea　changes　too　and　a　place　does　not　always



remain　land　or　sea　throughout　all　time；　but　where　there　was　dry　land



there　comes　to　be　sea；　and　where　there　is　now　sea；　there　one　day　comes



to　be　dry　land。　But　we　must　suppose　these　changes　to　follow　some　order



and　cycle。　The　principle　and　cause　of　these　changes　is　that　the



interior　of　the　earth　grows　and　decays；　like　the　bodies　of　plants



and　animals。　Only　in　the　case　of　these　latter　the　process　does　not



go　on　by　parts；　but　each　of　them　necessarily　grows　or　decays　as　a



whole；　whereas　it　does　go　on　by　parts　in　the　case　of　the　earth。　Here



the　causes　are　cold　and　heat；　which　increase　and　diminish　on　account



of　the　sun　and　its　course。　It　is　owing　to　them　that　the　parts　of　the



earth　come　to　have　a　different　character；　that　some　parts　remain　moist



for　a　certain　time；　and　then　dry　up　and　grow　old；　while　other　parts　in



their　turn　are　filled　with　life　and　moisture。　Now　when　places　become



drier　the　springs　necessarily　give　out；　and　when　this　happens　the



rivers　first　decrease　in　size　and　then　finally　become　dry；　and　when



rivers　change　and　disappear　in　one　part　and　come　into　existence



correspondingly　in　another；　the　sea　must　needs　be　affected。



　　If　the　sea　was　once　pushed　out　by　rivers　and　encroached　upon　the



land　anywhere；　it　necessarily　leaves　that　place　dry　when　it　recedes；



again；　if　the　dry　land　has　encroached　on　the　sea　at　all　by　a　process



of　silting　set　up　by　the　rivers　when　at　their　full；　the　time　must　come



when　this　place　will　be　flooded　again。



　　But　the　whole　vital　process　of　the　earth　takes　place　so　gradually



and　in　periods　of　time　which　are　so　immense　compared　with　the　length



of　our　life；　that　these　changes　are　not　observed；　and　before　their



course　can　be　recorded　from　beginning　to　end　whole　nations　perish



and　are　destroyed。　Of　such　destructions　the　most　utter　and　sudden



are　due　to　wars；　but　pestilence　or　famine　cause　them　too。　Famines；



again；　are　either　sudden　and　severe　or　else　gradual。　In　the　latter



case　the　disappearance　of　a　nation　is　not　noticed　because　some　leave



the　country　while　others　remain；　and　this　goes　on　until　the　land　is



unable　to　maintain　any　inhabitants　at　all。　So　a　long　period　of　time　is



likely　to　elapse　from　the　first　departure　to　the　last；　and　no　one



remembers　and　the　lapse　of　time　destroys　all　record　even　before　the



last　inhabitants　have　disappeared。　In　the　same　way　a　nation　must　be



supposed　to　lose　account　of　the　time　when　it　first　settled　in　a　land



that　was　changing　from　a　marshy　and　watery　state　and　becoming　dry。



Here；　too；　the　change　is　gradual　and　lasts　a　long　time　and　men　do



not　remember　who　came　first；　or　when；　or　what　the　land　was　like　when



they　came。　This　has　been　the　case　with　Egypt。　Here　it　is　obvious



that　the　land　is　continually　getting　drier　and　that　the　whole



country　is　a　deposit　of　the　river　Nile。　But　because　the　neighbouring



peoples　settled　in　the　land　gradually　as　the　marshes　dried；　the



lapse　of　time　has　hidden　the　beginning　of　the　process。　However；　all



the　mouths　of　the　Nile；　with　the　single　exception　of　that　at



Canopus；　are　obviously　artificial　and　not　natural。　And　Egypt　was



nothing　more　than　what　is　called　Thebes；　as　Homer；　too；　shows；



modern　though　he　is　in　relation　to　such　changes。　For　Thebes　is　the



place　that　he　mentions；　which　implies　that　Memphis　did　not　yet



exist；　or　at　any　rate　was　not　as　important　as　it　is　now。　That　this



should　be　so　is　natural；　since　the　lower　land　came　to　be　inhabited



later　than　that　which　lay　higher。　For　the　parts　that　lie　nearer　to　the



place　where　the　river　is　depositing　the　silt　are　necessarily　marshy



for　a　longer　time　since　the　water　always　lies　most　in　the　newly　formed



land。　But　in　time　this　land　changes　its　character；　and　in　its　turn



enjoys　a　period　of　prosperity。　For　these　places　dry　up　and　come　to



be　in　good　condition　while　the　places　that　were　formerly　well…tempered