meteorology-第24章

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！




mock　sun　is　a　surer　sign　of　rain　than　the　rods；　it　indicates；　more



than　they　do；　that　the　air　is　ripe　for　the　production　of　water。



Further　a　mock　sun　to　the　south　is　a　surer　sign　of　rain　than　one　to



the　north；　for　the　air　in　the　south　is　readier　to　turn　into　water　than



that　in　the　north。



　　Mock　suns　and　rods　are　found；　as　we　stated；　about　sunset　and



sunrise；　not　above　the　sun　nor　below　it；　but　beside　it。　They　are　not



found　very　close　to　the　sun；　nor　very　far　from　it；　for　the　sun



dissolves　the　cloud　if　it　is　near；　but　if　it　is　far　off　the　reflection



cannot　take　place；　since　sight　weakens　when　it　is　reflected　from　a



small　mirror　to　a　very　distant　object。　（This　is　why　a　halo　is　never



found　opposite　to　the　sun。）　If　the　cloud　is　above　the　sun　and　close　to



it　the　sun　will　dissolve　it；　if　it　is　above　the　sun　but　at　a



distance　the　sight　is　too　weak　for　the　reflection　to　take　place；　and



so　it　will　not　reach　the　sun。　But　at　the　side　of　the　sun；　it　is



possible　for　the　mirror　to　be　at　such　an　interval　that　the　sun　does



not　dissolve　the　cloud；　and　yet　sight　reaches　it　undiminished



because　it　moves　close　to　the　earth　and　is　not　dissipated　in　the



immensity　of　space。　It　cannot　subsist　below　the　sun　because　close　to



the　earth　the　sun's　rays　would　dissolve　it；　but　if　it　were　high　up　and



the　sun　in　the　middle　of　the　heavens；　sight　would　be　dissipated。



Indeed；　even　by　the　side　of　the　sun；　it　is　not　found　when　the　sun　is



in　the　middle　of　the　sky；　for　then　the　line　of　vision　is　not　close



to　the　earth；　and　so　but　little　sight　reaches　the　mirror　and　the



reflection　from　it　is　altogether　feeble。



　　Some　account　has　now　been　given　of　the　effects　of　the　secretion



above　the　surface　of　the　earth；　we　must　go　on　to　describe　its



operations　below；　when　it　is　shut　up　in　the　parts　of　the　earth。



　　Just　as　its　twofold　nature　gives　rise　to　various　effects　in　the



upper　region；　so　here　it　causes　two　varieties　of　bodies。　We　maintain



that　there　are　two　exhalations；　one　vaporous　the　other　smoky；　and



there　correspond　two　kinds　of　bodies　that　originate　in　the　earth；



'fossiles'　and　metals。　The　heat　of　the　dry　exhalation　is　the　cause



of　all　'fossiles'。　Such　are　the　kinds　of　stones　that　cannot　be　melted；



and　realgar；　and　ochre；　and　ruddle；　and　sulphur；　and　the　other



things　of　that　kind；　most　'fossiles'　being　either　coloured　lye　or；



like　cinnabar；　a　stone　compounded　of　it。　The　vaporous　exhalation　is



the　cause　of　all　metals；　those　bodies　which　are　either　fusible　or



malleable　such　as　iron；　copper；　gold。　All　these　originate　from　the



imprisonment　of　the　vaporous　exhalation　in　the　earth；　and　especially



in　stones。　Their　dryness　compresses　it；　and　it　congeals　just　as　dew　or



hoar…frost　does　when　it　has　been　separated　off；　though　in　the



present　case　the　metals　are　generated　before　that　segregation



occurs。　Hence；　they　are　water　in　a　sense；　and　in　a　sense　not。　Their



matter　was　that　which　might　have　become　water；　but　it　can　no　longer　do



so：　nor　are　they；　like　savours；　due　to　a　qualitative　change　in



actual　water。　Copper　and　gold　are　not　formed　like　that；　but　in　every



case　the　evaporation　congealed　before　water　was　formed。　Hence；　they



all　（except　gold）　are　affected　by　fire；　and　they　possess　an



admixture　of　earth；　for　they　still　contain　the　dry　exhalation。



　　This　is　the　general　theory　of　all　these　bodies；　but　we　must　take



up　each　kind　of　them　and　discuss　it　separately。







　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　Book　IV



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1







　　WE　have　explained　that　the　qualities　that　constitute　the　elements



are　four；　and　that　their　combinations　determine　the　number　of　the



elements　to　be　four。



　　Two　of　the　qualities；　the　hot　and　the　cold；　are　active；　two；　the　dry



and　the　moist；　passive。　We　can　satisfy　ourselves　of　this　by　looking　at



instances。　In　every　case　heat　and　cold　determine；　conjoin；　and



change　things　of　the　same　kind　and　things　of　different　kinds；



moistening；　drying；　hardening；　and　softening　them。　Things　dry　and



moist；　on　the　other　hand；　both　in　isolation　and　when　present



together　in　the　same　body　are　the　subjects　of　that　determination　and



of　the　other　affections　enumerated。　The　account　we　give　of　the



qualities　when　we　define　their　character　shows　this　too。　Hot　and



cold　we　describe　as　active；　for　'congregating'　is　essentially　a



species　of　'being　active'：　moist　and　dry　are　passive；　for　it　is　in



virtue　of　its　being　acted　upon　in　a　certain　way　that　a　thing　is　said



to　be　'easy　to　determine'　or　'difficult　to　determine'。　So　it　is



clear　that　some　of　the　qualities　are　active　and　some　passive。



　　Next　we　must　describe　the　operations　of　the　active　qualities　and　the



forms　taken　by　the　passive。　First　of　all；　true　becoming；　that　is；



natural　change；　is　always　the　work　of　these　powers　and　so　is　the



corresponding　natural　destruction；　and　this　becoming　and　this



destruction　are　found　in　plants　and　animals　and　their　parts。　True



natural　becoming　is　a　change　introduced　by　these　powers　into　the



matter　underlying　a　given　thing　when　they　are　in　a　certain　ratio　to



that　matter；　which　is　the　passive　qualities　we　have　mentioned。　When



the　hot　and　the　cold　are　masters　of　the　matter　they　generate　a



thing：　if　they　are　not；　and　the　failure　is　partial；　the　object　is



imperfectly　boiled　or　otherwise　unconcocted。　But　the　strictest　general



opposite　of　true　becoming　is　putrefaction。　All　natural　destruction



is　on　the　way　to　it；　as　are；　for　instance；　growing　old　or　growing　dry。



Putrescence　is　the　end　of　all　these　things；　that　is　of　all　natural



objects；　except　such　as　are　destroyed　by　violence：　you　can　burn；　for



instance；　flesh；　bone；　or　anything　else；　but　the　natural　course　of



their　destruction　ends　in　putrefaction。　Hence　things　that　putrefy



begin　by　being　moist　and　end　by　being　dry。　For　the　moist　and　the　dry



were　their　matter；　and　the　operation　of　the　active　qualities　caused



the　dry　to　be　determined　by　the　moist。



　　Destruction　supervenes　when　the　determined　gets　the　better　of　the



determining　by　the　help　of　the　environment　（though　in　a　special



sense　the　word　putrefaction　is　applied　to　partial　destruction；　when



a　thing's　nature　is　perverted）。　Hence　everything；　except　fire；　is



liable　to　putrefy；　for　earth；　water；　and　air　putrefy；　being　all　of



them　matter　relatively　to　fire。　The　definition　of　putrefaction　is：　the



destruction　of　the　peculiar　and　natural　heat　in　any　moist　subject　by



external　heat；　that　is；　by　the　heat　of　the　environment。　So　since



lack　of　heat　is　the　ground　of　this　affection　and　everything　in　as



far　as　it　lacks　heat　is　cold；　both　heat　and　cold　will　be　the　causes　of



putrefaction；　which　will　be　due　indifferently　to　cold　in　the



putrefying　subject　or　to　heat　in　the　environment。



　　This　explains　why　everything　that　putrefies　grows　drier　and　ends



by　becoming　earth　or　dung。　The　subject's　own　heat　departs　and　causes



the　natural　moisture　to　evaporate　with　it；　and　then　there　is　nothing



left　to　draw　in　moisture；　for　it　is　a　thing's　peculiar　heat　that



attracts　moisture　and　draws　it　in。　Again；　putrefaction　takes　place



less　in　cold　that　in　hot　seasons；　for　in　winter　the　surrounding　air



and　water　contain　but　little　heat　and　it　has　no　power；　but　in　summer



there　is　more。　Again；　what　is　frozen　does　not　putrefy；　for　its　cold　is



greater　that　the　heat　of　the　air　and　so　is　not　mastered；　whereas



what　affects　a　thing　does　master　it。　Nor　does　that　which　is　boiling　or



hot　putrefy；　for　the　heat　in　the　air　being　less　than　that　in　the



object　does　not　prevail　over　it　or　set　up　any　change。　So　too



anything　that　is　flowing　or　in　motion　is　less　apt　to　putrefy　than　a



thing　at　rest；　for　the　motion　set　up　by　the　heat　in　the　air　is



weaker　than　that　pre…existing　in　the　object；　and　so　it　causes　no



change。　For　the　same　reason　a　great　quantity　of　a　thing　putrefies　less