on sense and the sensible-第3章

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whenever　a　fiery　element　is　in　a　translucent　medium　presence　there



is　Light；　while　the　privation　of　it　is　Darkness。　But　the



'Translucent'；　as　we　call　it；　is　not　something　peculiar　to　air；　or



water；　or　any　other　of　the　bodies　usually　called　translucent；　but　is　a



common　'nature'　and　power；　capable　of　no　separate　existence　of　its



own；　but　residing　in　these；　and　subsisting　likewise　in　all　other



bodies　in　a　greater　or　less　degree。　As　the　bodies　in　which　it　subsists



must　have　some　extreme　bounding　surface；　so　too　must　this。　Here；　then；



we　may　say　that　Light　is　a　'nature'　inhering　in　the　Translucent　when



the　latter　is　without　determinate　boundary。　But　it　is　manifest　that；



when　the　Translucent　is　in　determinate　bodies；　its　bounding　extreme



must　be　something　real；　and　that　colour　is　just　this　'something'　we



are　plainly　taught　by　facts…colour　being　actually　either　at　the



external　limit；　or　being　itself　that　limit；　in　bodies。　Hence　it　was



that　the　Pythagoreans　named　the　superficies　of　a　body　its　'hue'；　for



'hue'；　indeed；　lies　at　the　limit　of　the　body；　but　the　limit　of　the



body；　is　not　a　real　thing；　rather　we　must　suppose　that　the　same



natural　substance　which；　externally；　is　the　vehicle　of　colour　exists



＇as　such　a　possible　vehicle＇　also　in　the　interior　of　the　body。



　　Air　and　water；　too　＇i。e。　as　well　as　determinately　bounded　bodies＇



are　seen　to　possess　colour；　for　their　brightness　is　of　the　nature　of



colour。　But　the　colour　which　air　or　sea　presents；　since　the　body　in



which　it　resides　is　not　determinately　bounded；　is　not　the　same　when



one　approaches　and　views　it　close　by　as　it　is　when　one　regards　it　from



a　distance；　whereas　in　determinate　bodies　the　colour　presented　is



definitely　fixed；　unless；　indeed；　when　the　atmospheric　environment



causes　it　to　change。　Hence　it　is　clear　that　that　in　them　which　is



susceptible　of　colour　is　in　both　cases　the　same。　It　is　therefore　the



Translucent；　according　to　the　degree　to　which　it　subsists　in　bodies



（and　it　does　so　in　all　more　or　less）；　that　causes　them　to　partake　of



colour。　But　since　the　colour　is　at　the　extremity　of　the　body；　it



must　be　at　the　extremity　of　the　Translucent　in　the　body。　Whence　it



follows　that　we　may　define　colour　as　the　limit　of　the　Translucent　in



determinately　bounded　body。　For　whether　we　consider　the　special



class　of　bodies　called　translucent；　as　water　and　such　others；　or



determinate　bodies；　which　appear　to　possess　a　fixed　colour　of　their



own；　it　is　at　the　exterior　bounding　surface　that　all　alike　exhibit



their　colour。



　　Now；　that　which　when　present　in　air　produces　light　may　be　present



also　in　the　Translucent　which　pervades　determinate　bodies；　or　again；



it　may　not　be　present；　but　there　may　be　a　privation　of　it。



Accordingly；　as　in　the　case　of　air　the　one　condition　is　light；　the



other　darkness；　in　the　same　way　the　colours　White　and　Black　are



generated　in　determinate　bodies。



　　We　must　now　treat　of　the　other　colours；　reviewing　the　several



hypotheses　invented　to　explain　their　genesis。



　　（1）　It　is　conceivable　that　the　White　and　the　Black　should　be



juxtaposed　in　quantities　so　minute　that　＇a　particle　of＇　either



separately　would　be　invisible；　though　the　joint　product　＇of　two



particles；　a　black　and　a　white＇　would　be　visible；　and　that　they　should



thus　have　the　other　colours　for　resultants。　Their　product　could；　at



all　events；　appear　neither　white　nor　black；　and；　as　it　must　have



some　colour；　and　can　have　neither　of　these；　this　colour　must　be　of　a



mixed



character…　in　fact；　a　species　of　colour　different　from　either。　Such；



then；　is　a　possible　way　of　conceiving　the　existence　of　a　plurality



of　colours　besides　the　White　and　Black；　and　we　may　suppose　that　＇of



this　'plurality'＇　many　are　the　result　of　a　＇numerical＇　ratio；　for



the　blacks　and　whites　may　be　juxtaposed　in　the　ratio　of　3　to　2　or　of　3



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