Next we learn, that the great reason why _pellucid_ bodies beaten small are white, is from the multitude of reflections, not from the particles of the body, but from the _contiguous_ surface of the air. And this is evidently manifested, by filling the _Interstitia_ of those powder’d bodies with Water, whereby their whiteness presently disappears. From the same reason proceeds the whiteness of many kinds of Sands, which in the _Microscope_ appear to be made up of a multitude of little _pellucid_ bodies, whose brightest reflections may by the _Microscope_ be plainly perceiv’d to come from their internal surfaces; and much of the whiteness of it may be destroy’d by the affusion of fair Water to be contiguous to those surfaces. The whiteness also of froth, is for the most part to be ascribed to the reflection of the light from the surface of the air within the Bubbles, and very little to the reflection from the surface of the Water it self: for this last reflection does not return a quarter so many Rays, as that which is made from the surface of the air, as I have certainly found by a multitude of Observations and Experiments. The whiteness of _Linnen_, _Paper_, _Silk_, &c. proceeds much from the same reason, as the _Microscope_ will easily discover; for the Paper is made up of an abundance of _pellucid_ bodies, which afford a very plentifull reflection from within, that is, from the concave surface of the air contiguous to its component particles; wherefore by the affusion of Water, Oyl, Tallow, Turpentine, &c. all those reflections are made more faint, and the beams of light are suffer’d to traject & run through the Paper more freely. Hence further we may learn the reason of the whiteness of many bodies, and by what means they may be in part made _pellucid_: As white Marble for instance, for this body is composed of a _pellucid_ body exceedingly flaw’d, that is, there are abundance of thin, and very fine cracks or chinks amongst the multitude of particles of the body, that contain in them small parcels of air, which do so _re-percuss_ and drive back the penetrating beams, that they cannot enter very deep within that body; which the _Microscope_ does plainly inform us to be made up of a _Congeries_ of _pellucid_ particles. And I further found it somewhat more evidently by some attempts I made towards the making transparent Marble, for by heating the Stone a little, and soaking it in Oyl, Turpentine, Oyl of Turpentine, &c., I found that I was able to see much deeper into the body of Marble than before; and one trial, which was not with an unctuous substance, succeeded better than the rest, of which, when I have a better opportunity, I shall make further trial.