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This also helps us to understand why the olfactory organ has its
proper seat in the environment of the brain； for cold matter is
potentially hot。 In the same way must the genesis of the eye be
explained。 Its structure is an offshoot from the brain； because the
latter is the moistest and coldest of all the bodily parts。
The organ of touch proper consists of earth； and the faculty of
taste is a particular form of touch。 This explains why the sensory
organ of both touch and taste is closely related to the heart。 For the
heart as being the hottest of all the bodily parts； is the
counterpoise of the brain。
This then is the way in which the characteristics of the bodily
organs of sense must be determined。
3
Of the sensibles corresponding to each sensory organ； viz。 colour；
sound； odour； savour； touch； we have treated in On the Soul in general
terms； having there determined what their function is； and what is
implied in their becoming actualized in relation to their respective
organs。 We must next consider what account we are to give of any one
of them； what； for example； we should say colour is； or sound； or
odour； or savour； and so also respecting ＇the object of＇ touch。 We
begin with colour。
Now； each of them may be spoken of from two points of view； i。e。
either as actual or as potential。 We have in On the Soul explained
in what sense the colour； or sound； regarded as actualized ＇for
sensation＇ is the same as； and in what sense it is different from； the
correlative sensation； the actual seeing or hearing。 The point of
our present discussion is； therefore； to determine what each
sensible object must be in itself； in order to be perceived as it is
in actual consciousness。
We have already in On the Soul stated of Light that it is the colour
of the Translucent； ＇being so related to it＇ incidentally； for
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。