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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 '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