meteorology-第21章

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them；　and　in　some　cold　in　so　far　as　heat　is　absent。　These　qualities；



then；　are　present　as　active；　and　the　moist　and　the　dry　as　passive；　and



consequently　all　four　are　found　in　mixed　bodies。　So　water　and　earth



are　the　constituents　of　homogeneous　bodies　both　in　plants　and　in



animals　and　of　metals　such　as　gold；　silver；　and　the　rest…water　and



earth　and　their　respective　exhalations　shut　up　in　the　compound　bodies；



as　we　have　explained　elsewhere。



　　All　these　mixed　bodies　are　distinguished　from　one　another；　firstly



by　the　qualities　special　to　the　various　senses；　that　is；　by　their



capacities　of　action。　（For　a　thing　is　white；　fragrant；　sonant；



sweet；　hot；　cold　in　virtue　of　a　power　of　acting　on　sense）。　Secondly　by



other　more　characteristic　affections　which　express　their　aptitude　to



be　affected：　I　mean；　for　instance；　the　aptitude　to　melt　or　solidify　or



bend　and　so　forth；　all　these　qualities；　like　moist　and　dry；　being



passive。　These　are　the　qualities　that　differentiate　bone；　flesh；



sinew；　wood；　bark；　stone　and　all　other　homogeneous　natural　bodies。　Let



us　begin　by　enumerating　these　qualities　expressing　the　aptitude　or



inaptitude　of　a　thing　to　be　affected　in　a　certain　way。　They　are　as



follows：　to　be　apt　or　inapt　to　solidify；　melt；　be　softened　by　heat；　be



softened　by　water；　bend；　break；　be　comminuted；　impressed；　moulded；



squeezed；　to　be　tractile　or　non…tractile；　malleable　or



non…malleable；　to　be　fissile　or　non…fissile；　apt　or　inapt　to　be　cut；



to　be　viscous　or　friable；　compressible　or　incompressible；



combustible　or　incombustible；　to　be　apt　or　inapt　to　give　off　fumes。



These　affections　differentiate　most　bodies　from　one　another。　Let　us　go



on　to　explain　the　nature　of　each　of　them。　We　have　already　given　a



general　account　of　that　which　is　apt　or　inapt　to　solidify　or　to



melt；　but　let　us　return　to　them　again　now。　Of　all　the　bodies　that



admit　of　solidification　and　hardening；　some　are　brought　into　this



state　by　heat；　others　by　cold。　Heat　does　this　by　drying　up　their



moisture；　cold　by　driving　out　their　heat。　Consequently　some　bodies　are



affected　in　this　way　by　defect　of　moisture；　some　by　defect　of　heat：



watery　bodies　by　defect　of　heat；　earthy　bodies　of　moisture。　Now



those　bodies　that　are　so　affected　by　defect　of　moisture　are



dissolved　by　water；　unless　like　pottery　they　have　so　contracted　that



their　pores　are　too　small　for　the　particles　of　water　to　enter。　All



those　bodies　in　which　this　is　not　the　case　are　dissolved　by　water；



e。g。　natron；　salt；　dry　mud。　Those　bodies　that　solidified　through



defect　of　heat　are　melted　by　heat；　e。g。　ice；　lead；　copper。　So　much　for



the　bodies　that　admit　of　solidification　and　of　melting；　and　those　that



do　not　admit　of　melting。



　　The　bodies　which　do　not　admit　of　solidification　are　those　which



contain　no　aqueous　moisture　and　are　not　watery；　but　in　which　heat



and　earth　preponderate；　like　honey　and　must　（for　these　are　in　a　sort



of　state　of　effervescence）；　and　those　which　do　possess　some　water



but　have　a　preponderance　of　air；　like　oil　and　quicksilver；　and　all



viscous　substances　such　as　pitch　and　birdlime。







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　　Those　bodies　admit　of　softening　which　are　not　（like　ice）　made　up



of　water；　but　in　which　earth　predominates。　All　their　moisture　must　not



have　left　them　（as　in　the　case　of　natron　and　salt）；　nor　must　the



relation　of　dry　to　moist　in　them　be　incongruous　（as　in　the　case　of



pottery）。　They　must　be　tractile　（without　admitting　water）　or　malleable



（without　consisting　of　water）；　and　the　agent　in　softening　them　is



fire。　Such　are　iron　and　horn。



　　Both　of　bodies　that　can　melt　and　of　bodies　that　cannot；　some　do



and　some　do　not　admit　of　softening　in　water。　Copper；　for　instance；



which　can　be　melted；　cannot　be　softened　in　water；　whereas　wool　and



earth　can　be　softened　in　water；　for　they　can　be　soaked。　（It　is　true



that　though　copper　can　be　melted　the　agent　in　its　case　is　not　water；



but　some　of　the　bodies　that　can　be　melted　by　water　too　such　as



natron　and　salt　cannot　be　softened　in　water：　for　nothing　is　said　to　be



so　affected　unless　the　water　soaks　into　it　and　makes　it　softer。）



Some　things；　on　the　other　hand；　such　as　wool　and　grain；　can　be



softened　by　water　though　they　cannot　be　melted。　Any　body　that　is　to　be



softened　by　water　must　be　of　earth　and　must　have　its　pores　larger　than



the　particles　of　water；　and　the　pores　themselves　must　be　able　to



resist　the　action　of　water；　whereas　bodies　that　can　be　'melted'　by



water　must　have　pores　throughout。



　　（Why　is　it　that　earth　is　both　'melted'　and　softened　by　moisture；



while　natron　is　'melted'　but　not　softened？　Because　natron　is



pervaded　throughout　by　pores　so　that　the　parts　are　immediately　divided



by　the　water；　but　earth　has　also　pores　which　do　not　connect　and　is



therefore　differently　affected　according　as　the　water　enters　by　one　or



the　other　set　of　pores。）



　　Some　bodies　can　be　bent　or　straightened；　like　the　reed　or　the　withy；



some　cannot；　like　pottery　and　stone。　Those　bodies　are　apt　to　be　bent



and　straightened　which　can　change　from　being　curved　to　being



straight　and　from　being　straight　to　being　curved；　and　bending　and



straightening　consist　in　the　change　or　motion　to　the　straight　or　to



a　curve；　for　a　thing　is　said　to　be　in　process　of　being　bent　whether　it



is　being　made　to　assume　a　convex　or　a　concave　shape。　So　bending　is



defined　as　motion　to　the　convex　or　the　concave　without　a　change　of



length。　For　if　we　added　'or　to　the　straight'；　we　should　have　a　thing



bent　and　straight　at　once；　and　it　is　impossible　for　that　which　is



straight　to　be　bent。　And　if　all　bending　is　a　bending　back　or　a　bending



down；　the　former　being　a　change　to　the　convex；　the　latter　to　the



concave；　a　motion　that　leads　to　the　straight　cannot　be　called　bending；



but　bending　and　straightening　are　two　different　things。　These；　then；



are　the　things　that　can；　and　those　that　cannot　be　bent；　and　be



straightened。



　　Some　things　can　be　both　broken　and　comminuted；　others　admit　only　one



or　the　other。　Wood；　for　instance；　can　be　broken　but　not　comminuted；



ice　and　stone　can　be　comminuted　but　not　broken；　while　pottery　may



either　be　comminuted　or　broken。　The　distinction　is　this：　breaking　is　a



division　and　separation　into　large　parts；　comminution　into　parts　of



any　size；　but　there　must　be　more　of　them　than　two。　Now　those　solids



that　have　many　pores　not　communicating　with　one　another　are



comminuible　（for　the　limit　to　their　subdivision　is　set　by　the



pores）；　but　those　whose　pores　stretch　continuously　for　a　long　way



are　breakable；　while　those　which　have　pores　of　both　kinds　are　both



comminuible　and　breakable。



　　Some　things；　e。g。　copper　and　wax；　are　impressible；　others；　e。g。



pottery　and　water；　are　not。　The　process　of　being　impressed　is　the



sinking　of　a　part　of　the　surface　of　a　thing　in　response　to　pressure　or



a　blow；　in　general　to　contact。　Such　bodies　are　either　soft；　like



wax；　where　part　of　the　surface　is　depressed　while　the　rest　remains；　or



hard；　like　copper。　Non…impressible　bodies　are　either　hard；　like



pottery　（its　surface　does　not　give　way　and　sink　in）；　or　liquid；　like



water　（for　though　water　does　give　way　it　is　not　in　a　part　of　it；　for



there　is　a　reciprocal　change　of　place　of　all　its　parts）。　Those



impressibles　that　retain　the　shape　impressed　on　them　and　are　easily



moulded　by　the　hand　are　called　'plastic'；　those　that　are　not　easily



moulded；　such　as　stone　or　wood；　or　are　easily　moulded　but　do　not



retain　the　shape　impressed；　like　wool　or　a　sponge；　are　not　plastic。



The　last　group　are　said　to　be　'squeezable'。　Things　are　'squeezable'



when　they　can　contract　into　themselves　under　pressure；　their　surface



sinking　in　without　being　broken　and　without　the　parts　interchanging



position　as　happens　in　the　case　of　water。　（We　speak　of　pressure　when



there　is　movement　and　the　motor　remains　in　contact　with　the　thing



moved；　of　impact　when　the　movement　is　due　to　the　local　movement　of　the



motor。）　Those　bodies　are　subject　to　squeezing　which　have　empty



pores…empty；　that　is；　of　the　stuff　of　which　the　body　itself



consists…and　that　can　sink　upon　the　void　spaces　within　them；　or　rather



upon　their　pores。　For　sometimes　the　pores　upon　which　a　body　sinks　in



are　not　empty　（a　wet　sponge；　for　instance；　has　its　pores　full）。　But



the　pores；　if　full；　must　be　full　of　something　softer　than　the　body



itself　which　is　to　contract。　Examples　of　things　squeezable　are　the



sponge；　wax；　flesh。　Those　things　are　not　squeezable　which　cannot　be



made　to　contract　upon　their　own　pores　by　pressure；　either　because　they



have　no　pores　or　because　their　pores　are　full　of　something　too　hard。



Thus　iron；　stone；　water　and　all　liquids　are　incapable　of　being



squeezed。



　　Things　are　tractile　when　their　surface　can　be　made　to　elongate；



for　being　drawn　out　is　a　movement　of　the　surface；　remaining



unbroken；　in　the　direction　of　the　mover。　Some　things　are　tractile；



e。g。　hair；　thongs；　sinew；　dough；　birdlime；　and　some　are　not；　e。g。



water；　stone。　Some　things　are　both　tractile　and　squeezable；　e。g。　wool；



in　other　cases　the　two　qualities　do　not　coincide；　phlegm；　for



instance；　is　tractile　but　not　squeezable；　and　a　sponge　squeezable



but　not　tractile。



　　Some　things　are　malleable；　like　copper。　Some　are　not；　like　stone　and



wood。　Things　are　malleable　when　their　surface　can　be　made　to　move　（but



only　in　part）　both　downwards　and　sideways　with　one　and　the　same



blow：　when　this　is　not　possible　a　body　is　not　malleable。　All　malleable



bodies　are　impressible；　but　not　all　impressible　bodies　are



malleable；　e。g。　wood；　though　on　the　whole　the　two　go　together。　Of



squeezable　things　some　are　malleable　and　some　not：　wax　and　mud　are



malleable；　wool　is　not。　Some　things　are　fissile；　e。g。　wood；　some　are



not；　e。g。　potter's　clay。　A　thing　is　fissile　when　it　is　apt　to　divide



in　advance　of　the　instrument　dividing　it；　for　a　body　is　said　to



split　when　it　divides　to　a　further　point　than　that　to　which　the



dividing　instrument　divides　it　and　the　act　of　division　advances：　which



is　not　the　case　with　cutting。　Those　bodies　which　cannot　behave　like



this　are　non…fissile。　Nothing　soft　is　fissile　（by　soft　I　mean



absolutely　soft　and　not　relatively：　for　iron　itself　may　be



relatively　soft）；　nor　are　all　hard　things　fissile；　but　only　such　as



are　neither　liquid　nor　impressible　nor　comminuible。　Such　are　the



bodies　that　have　the　pores　along　which　they　cohere　lengthwise　and



not　crosswise。



　　Those　hard　or　soft　solids　are　apt　to　be　cut　which　do　not　necessarily



either　split　in　advance　of　the　instrument　or　break　into　minute



fragments　when　they　are　being　divided。　Those　that　necessarily　do　so



and　liquids　cannot　be　cut。　Some　things　can　be　both　split　and　cut；　like



wood；　though　generally　it