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 maybe 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 baking it in Oyl, Turpentine, Oyl of Turpentine, &c., I found that I was able to see much deeper into the body of Marble then 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.