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