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