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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