293

Of Light and Colours.

F G, in the Point C, the Angle HCK,^ade by the incident Ray HC and the

P6rpen-

I s transparent, but the Froth, by reason of its Pores,Peonies opake; thus dry Paper is more opake than'hat which is wetted with Water or Oil, because morePorous. Thus the Oculus Mundi Stone is more opake^hen dry than when steeped in Water; and Glass re-cced to Powder is no longer transparent,k 7- Hence it follows, that the Parts of Bodies and their"res must not be less than a certain definite Bigness tosender them opake. For the opakest Bodies, if theirs^rts be subtilly divided, become perfectly transparent.

. hus Copper dissolved in Aqua-fortis has all its Par-oles pellucid, and the whole Solution is transparent,Pfius a Bubble blown of Soap-Water may become so*hin on the Top as to reflect no Light, but will trans-mit the whole. Thus Water, Salts, Glass, Stones, Vr.though they are as porous as other Bodies, yet theirParts and Interstices are too small to cause Reflections111 their common Surfaces.

y, 8. Therefore in all transparent Bodies, as BE FC, aof Light, as K L, falling on its Surface in the"mt L, will there be in Part reflected (as before) intot!le Ray L M j the other Part will go regularly on in a^ctilineal Direction from the upper to the lower Sur-at N, where meeting with the Air (a Medium of aAfferent Density) it will be in Part reflected again intoP 16 Ray NO; the other Part goes out to the Eye at p,°y which Means all the internal Parts from whence that? a y comes will be rendered visible to the Eye; and.'Hce this may be conceived of every Point in the Body,^ is easy to understand how the whole becomes trans-ient.

-8

Y. I have often found Gentlemen reflect with greatUr prize on the exceeding great Porosity of Bodies ne-Ce ssarily required for the Transmission of Light, andi at the same Time on the Hardness and Firmness ofParts of such Bodies, as Glass, for Instance, and°mers. But Sir Isaac Newton has put us into a MethodU 7 by

PlateXXXVI.Fig. 2.