the Surface of the same Extent, and how much these Qualities may serve to
produce Colour may be somewhat guess'd at, by that which happens in the
Agitation of Water; for if the Bubbles that are thereby made be Great, and
but Few, the Water will scarce acquire a sensible Colour, but if it be
reduc'd to a Froth, consisting of Bubbles, which being very Minute and
Contiguous to each other, are a multitude of them crowded into a narrow
Room, the Water (turned to Froth) does then exhibit a very manifest White
Colour,[3] (to which these last nam'd Conditions of the Bubbles do as well
as their Convex figure contribute) and that for Reasons to be mention'd
anon. Besides, it is not necessary that the Superficial particles that
exhibit one Colour, should be all of them Round, or all Conical, or all of
any one Shape, but Corpuscles of differing Figures may be mingled on the
Surface of the Opacous Body, as when the Corpuscles that make a Blew
colour, and those that make a Yellow, come to be Accurately and Skilfully
mix'd, they make up a Green, which though it seem one simple Colour, yet in
this case appears to be made by Corpuscles of very differing Kinds, duely
commix'd. Moreover the Figure and Bigness of the little Depressions,
Cavities, Furrows or Pores intercepted betwixt these protuberant
Corpuscles, are as well to be consider'd as the Sizes and Shapes of the
Corpuscles themselves: For we may conceive the Physical superficies of a
Body, where (as we said) its Colour does as it were reside, to be cut
Transversly by a Mathematical plain, which you know is conceiv'd to be
without any Depth or Thickness at all, and then as some parts of the
Physical Superficies will be Protuberant; or swell above this last plain,
so others may be depress'd beneath it; as (to explane my self by a gross
Comparison) in divers places of the Surface of the Earth, there are not
only Neighbouring Hills, Trees, &c. that are rais'd above the Horizontal
Level of the Valley, but Rivers, Wells, Pits and other Cavities that are
depress'd beneath it, and that such Protuberant and Concave parts of a
Surface may remit the Light so differingly, as much to vary a Colour, some