_The least parts of almost all natural Bodies are in some measure
transparent: And the Opacity of those Bodies ariseth from the multitude
of Reflexions caused in their internal Parts._
That this is so has been observed by others, and will easily be granted
by them that have been conversant with Microscopes. And it may be also
tried by applying any substance to a hole through which some Light is
immitted into a dark Room. For how opake soever that Substance may seem
in the open Air, it will by that means appear very manifestly
transparent, if it be of a sufficient thinness. Only white metalline
Bodies must be excepted, which by reason of their excessive density seem
to reflect almost all the Light incident on their first Superficies;
unless by solution in Menstruums they be reduced into very small
Particles, and then they become transparent.