_Note_, There are but three Affections of Light in which I have observ'd its Rays to differ; _viz._ Refrangibility, Reflexibility, and Colour; and those Rays which agree in Refrangibility, agree also in the other two, and therefore may well be defined Homogeneal; especially since Men usually call those things Homogeneal, which are so in all Qualities that come under their Knowledge, tho' in other Qualities, that their Knowledge extends not to, there may possibly be some Heterogeneity. 3. Those Colours I call Simple or Homogeneal, which are exhibited by Homogeneal Light. 4. And those Compound or Heterogeneal, which are exhibited by Heterogeneal Light. 5. Different Colours, I call, not only the more eminent Species, Red, Yellow, Green, Blue, Purple, but all other the minutest Gradations; much after the same manner, that not only the more eminent Degrees in Musick, but all the lead Gradations, are esteem'd different Sounds. _PROPOSITIONS._ 1. The Sun's Light consists of Rays differing by indefinite Degrees of Refrangibility. 2. Rays which differ in Refrangibility, when parted from one another, do proportionally differ in the Colours which they exhibit. These Two Propositions are Matter of Fact. 3. There are as many Simple or Homogeneal Colours, as Degrees of Refrangibility. For to every Degree of Refrangibility belongs a different Colour, by _Prop._ 2. and that Colour is Simple, by _Def._ 1, and 3. 4. Whiteness, in all respects like that of the Sun's immediate Light, and of all the usual Objects of our Senses, cannot be compounded of two Simple Colours alone. For such a Composition must be made by Rays that have only two Degrees of Refrangibility, by _Def._ 1 and 3. and therefore it cannot be like that of the Sun's Light. by _Prop._ 1. nor, for the same Reason, like that of ordinary white Objects. 5. Whiteness, in all respects, like that of the Sun's immediate Light, cannot be compounded of Simple Colours without an indefinite Variety of them. For to such a Composition, there are requisite Rays endu'd with all the indefinite Degrees of Refrangibility, by _Prop._ 1. And those infer as many Simple Colours, by _Def._ 1 and 3. and _Prop._ 2 and 3. To make these a little plainer, I have added also the Propositions that follow. 6. The Rays of Light do not act on one another, in passing through the same Medium. 7. The Rays of Light suffer not any change of their Qualities from Refraction.