8. Nor afterwards from the adjacent quiet _Medium_: These two Propositions are manifest _de Facto_ in Homogeneal Light, whose Colour and Refrangibility is not at all changeable, either by Refraction, or by the Contermination of a quiet _Medium_. And as for Heterogeneal Light, it is but an Aggregate of several sorts of Homogeneal Light, no one sort of which suffers any more alteration than if it were alone; because the Rays act not on one another, by _Prop._ 6. and therefore the Aggregate can suffer none. These two Propositions also might be further proved apart, by Experiments too long to be here described. 9. There can no Homogeneal Colours be reduced out of Light by Refraction, which were not commixt in it before. Because by _Prop._ 7. and 8. Refraction changeth not the Qualities of the Rays, but only separates those which have divers Qualities, by means of their different Refrangibility. 10. The Sun's Light is an Aggregate of an indefinite variety of Homogeneal Colours, by _Prop._ 1, 3, and 9. And hence it is, that I call Homogeneal Colours also Primitive or Original. And thus much concerning Colours. _For a further Illustration of this Doctrine, Mr. _Newton_, in his Book of Opticks lately published, has by undeniable Experiments explained most of the Principal Phænomena of Light and Colours: To which we refer the Reader._ _A Demonstration concerning the Motion of Light, communicated from _Paris_._ Philosophers have been labouring for many Years to decide by some Experiment, whether the Action of Light be conveyed in an instant to distant Places, or whether it requireth time. M. _Romer_, of the _Royal Academy_ of Sciences, hath devised a way taken from the Observations of the first Satellit of _Jupiter_, by which he demonstrates, that for the distance of about 3000 Leagues, such as is very near the bigness of the Diameter of the Earth, Light needs not one Second of Time. Let (in _Fig. 3. Plate 3._) _A_ be the _Sun_, _B_ _Jupiter_, _C_ the first Satellit of _Jupiter_, which enters into the shadow of _Jupiter_, to come out at _D_, and let _EFGHKL_ be the _Earth_, placed at divers distances from _Jupiter_.