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！
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 onl