_MADAM,_
I cannot perceive the Rational Truth of your _Authors_ opinion,
concerning _Colours_, made _by the agitation of little spherical bodies
of an Æthereal matter, transmitting the action of Light_; for if
colours were made after this manner, there would, in my opinion, not
be any fixed or lasting colour, but one colour would be so various,
and change faster then every minute; the truth is, there would be
no certain or perfect colour at all: wherefore it seems altogether
improbable, that such liquid, rare and disunited bodies should either
keep or make inherent and fixed colours; for liquid and rare bodies,
whose several parts are united into one considerable bulk of body,
their colours are more apt to change then the colours of those bodies
that are dry, solid and dense; the reason is, that rare and liquid
bodies are more loose, slack, and agil, then solid and dry bodies, in
so much, as in every alteration of motion their colours are apt to
change: And if united rare and liquid bodies be so apt to alter and
change, how is it probable, that those bodies, which are small and
not united, should either keep or make inherent fixed colours? I will
not say, but that such little bodies may range into such lines and
figures, as make colours, but then they cannot last, being not united
into a lasting body, that is, into a solid, substantial body, proper
to make such figures as colours. But I desire you not to mistake me,
_Madam_, for I do not mean, that the substance of colours is a gross
thick substance, for the substance may be as thin and rare as flame or
light, or in the next degree to it; for certainly the substance of
light, and the substance of colours come in their degrees very neer
each other; But according to the contraction of the figures, colours
are paler or deeper, or more or less lasting. And as for the reason,
why colours will change and rechange, it is according as the figures
alter or recover their forms; for colours will be as animal Creatures,
which sometimes are faint, pale, and sick, and yet recover; but when
as a particular colour is, as I may say, quite dead, then there is no
recovering of it. But colours may seem altered sometimes in our eyes,
and yet not be altered in themselves; for our eyes, if perfect, see
things as they are presented; and for proof, if any animal should be
presented in an unusual posture or shape, we could not judg of it;
also if a Picture, which must be viewed side-wards, should be looked
upon forwards, we could not know what to make of it; so the figures
of colours, if they be not placed rightly to the sight, but turned
topsie-turvie as the Phrase is, or upside-down, or be moved too quick,
and this quick motion do make a confusion with the lines of Light, we
cannot possibly see the colour perfectly. Also several lights or shades
may make colours appear otherwise then in themselves they are, for
some sorts of lights and shades may fall upon the substantial figures
of colours in solid bodies, in such lines and figures, as they may
over-power the natural or artificial inherent colours in solid bodies,
and for a time make other colours, and many times the lines of light
or of shadows will meet and sympathize so with inherent colours, and
place their lines so exactly, as they will make those inherent colours
more splendorous then in their own nature they are, so that light and
shadows will add or diminish or alter colours very much. Likewise some
sorts of colours will be altered to our sight, not by all, but onely by
some sorts of light, as for example, blew will seem green, and green
blew by candle light, when as other colours will never appear changed,
but shew constantly as they are; the reason is, because the lines of
candle light fall in such figures upon the inherent colours, and so
make them appear according to their own figures; Wherefore it is onely
the alteration of the exterior figures of light and shadows, that make
colours appear otherwise, and not a change of their own natures; And
hence we may rationally conclude, that several lights and shadows by
their spreading and dilating lines may alter the face or out-side of
colours, but not suddenly change them, unless the power of heat, and
continuance of time, or any other cause, do help and assist them in
that work of metamorphosing or transforming of colours; but if the
lines of light be onely, as the phrase is, Skin-deep; that is, but
lightly spreading and not deeply penetrating, they may soon wear out or
be rubbed off; for though they hurt, yet they do not kill the natural
colour, but the colour may recover and reassume its former vigour and
lustre: but time and other accidental causes will not onely alter, but
destroy particular colours as well as other creatures, although not all
after the same manner, for some will last longer then others. And thus,
_Madam_, there are three sorts of Colours, Natural, Artificial, and
Accidental; but I have discoursed of this subject more at large in my
Philosophical Opinions, to which I refer you, and rest,
Madam,
_Your faithful Friend_
_and Servant._