on sense and the sensible-第3部分

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to　4；　or　in　ratios　expressible　by　other　numbers；　while　some　may　be



juxtaposed　according　to　no　numerically　expressible　ratio；　but



according　to　some　relation　of　excess　or　defect　in　which　the　blacks　and



whites　involved　would　be　incommensurable　quantities；　and；　accordingly；



we　may　regard　all　these　colours　＇viz。　all　those　based　on　numerical



ratios＇　as　analogous　to　the　sounds　that　enter　into　music；　and



suppose　that　those　involving　simple　numerical　ratios；　like　the



concords　in　music；　may　be　those　generally　regarded　as　most



agreeable；　as；　for　example；　purple；　crimson；　and　some　few　such



colours；　their　fewness　being　due　to　the　same　causes　which　render　the



concords　few。　The　other　compound　colours　may　be　those　which　are　not



based　on　numbers。　Or　it　may　be　that；　while　all　colours　whatever



＇except　black　and　white＇　are　based　on　numbers；　some　are　regular　in



this　respect；　others　irregular；　and　that　the　latter　＇though　now



supposed　to　be　all　based　on　numbers＇；　whenever　they　are　not　pure；



owe　this　character　to　a　corresponding　impurity　in　＇the　arrangement　of＇



their　numerical　ratios。　This　then　is　one　conceivable　hypothesis　to



explain　the　genesis　of　intermediate　colours。



　　（2）　Another　is　that　the　Black　and　White　appear　the　one　through　the



medium　of　the　other；　giving　an　effect　like　that　sometimes　produced



by　painters　overlaying　a　less　vivid　upon　a　more　vivid　colour；　as



when　they　desire　to　represent　an　object　appearing　under　water　or



enveloped　in　a　haze；　and　like　that　produced　by　the　sun；　which　in



itself　appears　white；　but　takes　a　crimson　hue　when　beheld　through　a



fog　or　a　cloud　of　smoke。　On　this　hypothesis；　too；　a　variety　of　colours



may　be　conceived　to　arise　in　the　same　way　as　that　already　described；



for　between　those　at　the　surface　and　those　underneath　a　definite　ratio



might　sometimes　exist；　in　other　cases　they　might　stand　in　no



determinate　ratio。　To　＇introduce　a　theory　of　colour　which　would　set



all　these　hypotheses　aside；　and＇　say　with　the　ancients　that　colours



are　emanations；　and　that　the　visibility　of　objects　is　due　to　such　a



cause；　is　absurd。　For　they　must；　in　any　case；　explain　sense…perception



through　Touch；　so　that　it　were　better　to　say　at　once　that　visual



perception　is　due　to　a　process　set　up　by　the　perceived　object　in　the



medium　between　this　object　and　the　sensory　organ；　due；　that　is；　to



contact　＇with　the　medium　affected；＇　not　to　emanations。



　　If　we　accept　the　hypothesis　of　juxtaposition；　we　must　assume　not



only　invisible　magnitude；　but　also　imperceptible　time；　in　order　that



the　succession　in　the　arrival　of　the　stimulatory　movements　may　be



unperceived；　and　that　the　compound　colour　seen　may　appear　to　be　one；



owing　to　its　successive　parts　seeming　to　present　themselves　at　once。



On　the　hypothesis　of　superposition；　however；　no　such　assumption　is



needful：　the　stimulatory　process　produced　in　the　medium　by　the　upper



colour；　when　this　is　itself　unaffected；　will　be　different　in　kind　from



that　produced　by　it　when　affected　by　the　underlying　colour。　Hence　it



presents　itself　as　a　different　colour；　i。e。　as　one　which　is　neither



white　nor　black。　So　that；　if　it　is　impossible　to　suppose　any　magnitude



to　be　invisible；　and　we　must　assume　that　there　is　some　distance　from



which　every　magnitude　is　visible；　this　superposition　theory；　too　＇i。e。



as　well　as　No。　3　infra＇；　might　pass　as　a　real　theory　of



colour…mixture。　Indeed；　in　the　previous　case　also　there　is　no　reason



why；　to　persons　at　a　distance　from　the　juxtaposed　blacks　and　whites；



some　one　colour　should　not　appear　to　present　itself　as　a　blend　of



both。　＇But　it　would　not　be　so　on　a　nearer　view＇；　for　it　will　be　shown；



in　a　discussion　to　be　undertaken　later　on；　that　there　is　no



magnitude　absolutely　invisible。



　　（3）　There　is　a　mixture　of　bodies；　however；　not　merely　such　as　some



suppose；　i。e。　by　juxtaposition　of　their　minimal　parts；　which；　owing　to



＇the　weakness　of　our＇　sense；　are　imperceptible　by　us；　but　a　mixture　by



which　they　＇i。e。　the　'matter'　of　which　they　consist＇　are　wholly



blent　together　by　interpenetration；　as　we　have　described　it　in　the



treatise　on　Mixture；　where　we　dealt　with　this　subject　generally　in　its



most　comprehensive　aspect。　For；　on　the　supposition　we　are　criticizing；



the　only　totals　capable　of　being　mixed　are　those　which　are　divisible



into　minimal　parts；　＇e。g。　genera　into　individuals＇　as　men；　horses；



or　the　＇various　kinds　of＇　seeds。　For　of　mankind　as　a　whole　the



individual　man　is　such　a　least　part；　of　horses　＇as　an　aggregate＇　the



individual　horse。　Hence　by　the　juxtaposition　of　these　we　obtain　a



mixed　total；　consisting　＇like　a　troop　of　cavalry＇　of　both　together；



but　we　do　not　say　that　by　such　a　process　any　individual　man　has　been



mixed　with　any　individual　horse。　Not　in　this　way；　but　by　complete



interpenetration　＇of　their　matter＇；　must　we　conceive　those　things　to



be　mixed　which　are　not　divisible　into　minima；　and　it　is　in　the　case　of



these　that　natural　mixture　exhibits　itself　in　its　most　perfect　form。



We　have　explained　already　in　our　discourse　'On　Mixture'　how　such



mixture　is　possible。　This　being　the　true　nature　of　mixture；　it　is



plain　that　when　bodies　are　mixed　their　colours　also　are　necessarily



mixed　at　the　same　time；　and　＇it　is　no　less　plain＇　that　this　is　the



real　cause　determining　the　existence　of　a　plurality　of　colours…　not



superposition　or　juxtaposition。　For　when　bodies　are　thus　mixed；



their　resultant　colour　presents　itself　as　one　and　the　same　at　all



distances　alike；　not　varying　as　it　is　seen　nearer　or　farther　away。



　　Colours　will　thus；　too　＇as　well　as　on　the　former　hypotheses＇；　be



many　in　number　on　account　of　the　fact　that　the　ingredients　may　be



combined　with　one　another　in　a　multitude　of　ratios；　some　will　be　based



on　determinate　numerical　ratios；　while　others　again　will　have　as　their



basis　a　relation　of　quantitative　excess　or　defect　not　expressible　in



integers。　And　all　else　that　was　said　in　reference　to　the　colours；



considered　as　juxtaposed　or　superposed；　may　be　said　of　them　likewise



when　regarded　as　mixed　in　the　way　just　described。



　　Why　colours；　as　well　as　savours　and　sounds；　consist　of　species



determinate　＇in　themselves＇　and　not　infinite　＇in　number＇　is　a　question



which　we　shall　discuss　hereafter。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　4







　　We　have　now　explained　what　colour　is；　and　the　reason　why　there　are



many　colours；　while　before；　in　our　work　On　the　Soul；　we　explained



the　nature　of　sound　and　voice。　We　have　next　to　speak　of　Odour　and



Savour；　both　of　which　are　almost　the　same　physical　affection；　although



they　each　have　their　being　in　different　things。　Savours；　as　a　class；



display　their　nature　more　clearly　to　us　than　Odours；　the　cause　of



which　is　that　the　olfactory　sense　of　man　is　inferior　in　acuteness　to



that　of　the　lower　animals；　and　is；　when　compared　with　our　other



senses；　the　least　perfect　of　Man's　sense　of　Touch；　on　the　contrary；



excels　that　of　all　other　animals　in　fineness；　and　Taste　is　a



modification　of　Touch。



　　Now　the　natural　substance　water　per　se　tends　to　be　tasteless。　But



＇since　without　water　tasting　is　impossible＇　either　（a）　we　must　suppose



that　water　contains　in　itself　＇uniformly　diffused　through　it＇　the



various　kinds　of　savour；　already　formed；　though　in　amounts　so　small　as



to　be　imperceptible；　which　is　the　doctrine　of　Empedocles；　or　（b）　the



water　must　be　a　sort　of　matter；　qualified；　as　it　were；　to　produce



germs　of　savours　of　all　kinds；　so　that　all　kinds　of　savour　are



generated　from　the　water；　though　different　kinds　from　its　different



parts；　or　else　（c）　the　water　is　in　itself　quite　undifferentiated　in



respect　of　savour　＇whether　developed　or　undeveloped＇；　but　some



agent；　such　for　example　as　one　might　conceive　Heat　or　the　Sun　to　be；



is　the　efficient　cause　of　savour。



　　（a）　Of　these　three　hypotheses；　the　falsity　of　that　held　by



Empedocles　is　only　too　evident。　For　we　see　that　when　pericarpal　fruits



are　plucked　＇from　the　tree＇　and　exposed　in　the　sun；　or　subjected　to



the　action　of　fire；　their　sapid　juices　are　changed　by　the　heat；



which　shows　that　their　qualities　are　not　due　to　their　drawing　anything



from　the　water　in　the　ground；　but　to　a　change　which　they　undergo



within　the　pericarp　itself；　and　we　see；　moreover；　that　these　juices；



when　extracted　and　allowed　to　lie；　instead　of　sweet　become　by　lapse　of



time　harsh　or　bitter；　or　acquire　savours　of　any　and　every　sort；　and



that；　again；　by　the　process　of　boiling　or　fermentation　they　are　made



to　assume　almost　all　kinds　of　new　savours。



　　（b）　It　is　likewise　impossible　that　water　should　be　a　material



qualified　to　generate　all　kinds　of　Savour　germs　＇so　that　different



savours　should　arise　out　of　different　parts　of　the　water＇；　for　we



see　different　kinds　of　taste　generated　from　the　same　water；　having



it　as　their　nutriment。



　　（C）　It　remains；　therefore；　to　suppose　that　the　water　is　changed　by



passively　receiving　some　affection　from　an　external　agent。　Now；　it



is　manifest　that　water　does　not　contract　the　quality　of　sapidity



from　the　agency　of　Heat　alone。　For　water　is　of　all　liquids　the



thinnest；　thinner　even　than　oil　itself；　though　oil；　owing　to　its



viscosity；　is　more　ductile　than　water；　the　latter　being　uncohesive



in　its　particles；　whence　water　is　more　difficult　than　oil　to　hold　in



the　hand　without　spilling。　But　since　perfectly　pure　water　does　not；



when　subjected　to　the　action　of　Heat；　show　any　tendency　to　acquire



consistency；　we　must　infer　that　some　other　agency　than　heat　is　the



cause　of　sapidity。　For　all　savours　＇i。e。　sapid　liquors＇　exhibit　a



comparative　consistency。　Heat　is；　however；　a　coagent　in　the　matter。



　　Now　the　sapid　juices　found　in　pericarpal　fruits　evidently　exist　also



in　the　earth。　Hence　many　of　the　old　natural　philosophers　assert　that