1. There are you know, _Pyrophilus_, besides those Obsolete Opinions about
Colours which have been long since Rejected, very Various Theories that
have each of them, even at this day, Eminent Men for its Abetters; for the
Peripatetick Schools, though they dispute amongst themselves divers
particulars concerning Colours, yet in this they seem Unanimously enough to
Agree, that Colours are Inherent and Real Qualities, which the Light doth
but Disclose, and not concurr to Produce. Besides there are _Moderns_, who
with a slight Variation adopt the Opinion of _Plato_, and as he would have
Colour to be nothing but a Kind of Flame consisting of Minute Corpuscles as
it were Darted by the Object against the Eye, to whose Pores their
Littleness and Figure made them congruous, so these would have Colour to be
an Internal Light of the more Lucid parts of the Object, Darkned and
consequently Alter'd by the Various Mixtures of the less Luminous parts.
There are also others, who in imitation of some of the Ancient _Atomists_,
make Colour not to be Lucid steam, but yet a Corporeal _Effluvium_ issuing
out of the Colour'd Body, but the Knowingst of these have of late Reform'd
their Hypothesis, by acknowledging and adding that some External Light is
necessary to Excite, and as _they_ speak, Sollicit these Corpuscles of
Colour as _they_ call them, and Bring them to the Eye. Another and more
principal Opinion of the _Modern_ Philosophers, to which this last nam'd
may by a Favourable explication be reconcil'd, is that which derives
Colours from the Mixture of Light and Darkness, or rather Light and
Shadows. And as for the _Chymists_ 'tis known, that the generality of them
ascribes the Origine of Colours to the Sulphureous Principle in Bodies,
though I find, as I elsewhere largely shew, that some of the Chiefest of
them derive Colours rather from Salt than Sulphur, and others, from the
third Hypostatical Principle, _Mercury_. And as for the _Cartesians_ I need
not tell you, that they, supposing the Sensation of Light to bee produc'd
by the Impulse made upon the Organs of Sight, by certain extremely Minute
and Solid Globules, to which the Pores of the Air and other Diaphanous
bodies are pervious, endeavour to derive the Varieties of Colours from the
Various Proportion of the Direct Progress or Motion of these Globules to
their Circumvolution or Motion about their own Centre, by which Varying
Proportion they are by this Hypothesis suppos'd qualify'd to strike the
Optick Nerve after several Distinct manners, so to produce the perception
of Differing Colours.
2. Besides these six principal Hypotheses, _Pyrophilus_, there may be some
others, which though Less known, may perhaps as well as thesc deserve to be
taken into consideration by you; but that I should copiously debate any of
them at present, I presume you will not expect, if you consider the Scope
of these Papers, and the Brevity I have design'd in them, and therefore I
shall at this time only take notice to you in the general of two or three
things that do more peculiarly concern the Treatise you have now in your
hands.
3. And first, though the Embracers of the Several Hypotheses I have been
naming to you, by undertaking each Sect of them to explicate Colours
indefinitely, by the particular Hypotheses they maintain, seem to hold it
forth as the only Needful Theory about that Subject, yet for my part I
doubt whether any one of all these Hypotheses have a right to be admitted
Exclusively to all others, for I think it Probable, that Whiteness and
Blackness may be explicated by Reflection alone without Refraction, as
you'l find endeavour'd in the Discourse you'l meet with e're long Of the
Origine of Whiteness and Blackness, and on the other side, since I have not
found that by any Mixture of White and True Black, (for there is a Blewish
Black which many mistake for a Genuine) there can be a Blew, a Yellow, or a
Red, to name no other Colours, produced, and since we do find that these
Colours may be produc'd in the Glass-prism and other Transparent bodies, by
the help of Refractions, it seems that Refraction is to be taken in into
the Explication of some Colours, to whose Generation they seem to concurr,
either by making a further or other Commixture of Shades with the Refracted
Light, or by some other way not now to be discours'd. And as it seems not
improbable, that in case the Pores of the Air, and other Diaphanous bodies
be every where almost fill'd with such _Globuli_ as the _Cartesians_
suppose, the Various kind of Motion of these _Globuli_, may in many cases
have no small stroak in Varying our Perception of Colour, so without the
Supposition of these _Globuli_, which 'tis not so easie to evince, I think
we may probably enough conceive in general, that the Eye may be Variously
affected, not only by the Entire Beams of Light that fall upon it as they
are such, but by the Order, and by the Degree of Swiftness, and in a word
by the Manner according to which the Particles that compose each Particular
Beam arrive at the Sensory, so that whatever be the Figure of the Little
Corpuscles, of which the Beams of Light consist, not only the Celerity or
Slowness of their Revolution or Rotation in reference to their Progressive
Motion, but their more Absolute Celerity, their Direct or Undulating
Motion, and other Accidents, which may attend their Appulse to the Eye, may
fit them to make Differing Impressions on it.
4. Secondly, For these and the like Considerations, _Pyrophilus_, I must
desire that you would look upon this little Treatise, not as a Discourse
written Principally to maintain any of the fore-mention'd Theories,
Exclusively to all others, or substitute a New one of my Own, but as the
beginning of a History of Colours, upon which, when you and your Ingenious
friends shall have Enrich'd it, a Solid Theory may be safely built. But yet
because this History is not meant barely for a Register of the things
recorded in it, but for an _Apparatus_ to a sound and comprehensitive
Hypothesis, I thought fit, so to temper the whole Discourse, as to make it
as conducible, as conveniently I can to that End, and therefore I have not
scrupled to let you see that I was willing, as to save you the labour of
Cultivating some Theories that I thought would never enable you to reach
the Ends you aim at, so to contract your Enquiries into a Narrow compass,
for both which purposes I thought it requisite to do these two things, the
_One_, to set down some Experiments which by the help of the Reflections
and Insinuations that attend them, may assist you to discover the
Infirmness and Insufficiency both of the common Peripatetick Doctrine, and
of the now more applauded Theory of the _Chymists_ about Colour, because
those two Doctrines having Possess'd themselves, the one of the most part
of the Schools, and the other of the Esteem of the Generality ef Physicians
and other Learned Men, whose Professions and Ways of Study do not exact
that they should Scrupulously examine the very First and Simplest
Principles of Nature, I fear'd it would be to little purpose, without doing
something to discover the Insufficiency of these Hypotheses, that I should,
(which was the _Other_ thing I thought requisite for me to do) set down
among my other Experiments those in the greatest Number, that may let you
see, that, till I shall be Better Inform'd, I encline to take Colour to be
a Modification of Light, and would invite you chiefly to Cultivate that
Hypothesis, and Improve it to the making out of the Generation of
Particular Colours, as I have Endeavour'd to apply it to the Explication of
Whiteness and Blackness.
5. Thirdly. But, _Pyrophilus_, though this be at present the Hypothesis I
preferr, yet I propose it but in a General Sense, teaching only that the
Beams of Light, Modify'd by the Bodies whence they are sent (Reflected or
Refracted) to the Eye, produce there that Kind of Sensation, Men commonly
call Colour; But whether I think this Modification of the Light to be
perform'd by Mixing it with Shades, or by Varying the Proportion of the
Progress and Rotation of the _Cartesian Globuli Cælestes_, or by some other
way which I am not now to mention, I pretend not here to Declare. Much less
do I pretend to Determine, or scarce so much as to Hope to know all that
were requisite to be Known, to give You, or even my Self, a perfect account
of the Theory of Vision and Colours, for in Order to such an undertaking I
would first Know what Light is, and if it be a Body (as a Body or the
Motion of a Body it seems to be) what Kind of Corpuscles for Size and Shape
it consists of, with what Swiftness they move Forwards, and Whirl about
their own Centres. Then I would Know the Nature of Refraction, which I take
to be one of the Abstrusest things (not to explicate Plausibly, but to
explicate Satisfactorily) that I have met with in Physicks; I would further
Know what Kind and what Degree of Commixture of Darkness or Shades is made
by Refractions or Reflections, or both, in the Superficial particles of
those Bodies, that being Shin'd upon, constantly exhibit the one, for
Instance, a Blew, the other a Yellow, the third a Red Colour; I would
further Know why this Contemperation of Light and Shade, that is made, for
Example, by the Skin of a Ripe Cherry, should exhibit a Red, and not a
Green, and the Leaf of the same Tree should exhibit a Green rather than a
Red; and indeed, Lastly, why since the Light that is Modify'd into these
Colours consists but of Corpuscles moved against the _Retina_ or Pith of
the Optick Nerve, it should there not barely give a Stroak, but produce a
Colour, whereas a Needle wounding likewise the Eye, would not produce
Colour but Pain. These, and perhaps other things I should think requisite
to be Known, before I should judge my Self to have fully Comprehended the
True and Whole Nature of Colours; and therefore, though by making the
Experiments and Reflections deliver'd in this Paper, I have endeavour'd
somewhat to Lessen my Ignorance in this Matter, and think it far more
Desireable to discover a Little, than to discover Nothing, yet I pretend
but to make it Probable by the Experiments I mention, that some Colours may
be Plausibly enough Explicated in the General by the Doctrine here
propos'd; For whensoever I would Descend to the Minute and Accurate
Explication of Particulars, I find my Self very Sensible of the great
Obscurity of things, without excepting those which we never see but when
they are Enlightned, and confess with _Scaliger_[5], _Latet natura hæc_,
(says he, Speaking of that of Colour) _& sicut aliarum rerum species in
profundissima caligine inscitiæ humanæ._
[5] Exercitat. 325 Parag. 4
* * * * *
_THE_
_EXPERIMENTAL HISTORY_
_OF COLOURS._
* * * * *