Microc RAP HA 7 83 
And that this was the furface.of the Air that gave fo vivid a re-percnf- 
fort try'd by this means. I funk half of a feria in Water, fo that: only | 
Water was contiguous to. the under furtace, and_then the internal re-» 
flection was{o exceedingly faint, that it was fcarce difcernable.... Again, 
I try'd to alter this vivid reflection by keeping off the Air, with a body. 
not fluid, and. that was by rubbing and holding my, finger very hard 
againft the under furface, {o as in many places the pulp of my finger did 
‘touch the Glafs, without.any izterjacent air between; thenobferving the 
reflection, I found,that wherefoever my finger or fkin toucht the furface, 
from that part there was no reflection, but in the little furrows or creafes 
of my fkin, where there remain‘d little {mall lines of air,from them was 
return'd a very vivid reflection as before. 1 try’d further,by making the 
furface of very pure Quickfilver to be contiguous to the under furface 
of this pe/ucid body> and then the reflection from that was fo exceeding- 
. ly more vivid than from the air, as the reflection from air was than 
the reflection from the Water; from all which trials I plainly faw, that 
the {trong reflecting air was the caufe of this Phenomenon. <i 
_ And this agrees very well with the Hypetbefis of light and PeLucid bo- 
dies which I have mention’d in the defcription of Affcovy-glaff;, for we 
there fuppofe Glafs to be a wzediunzwhich does lefS refift the pulfe of light, 
and confequently,that moft of the Raysincident on it enter intoi ey are 
refracted towards the perpendicular ; whereas the air I fuppofe to be a 
body that does more refiftit, and confequently more are re-percafs d then 
do enter it; the fame kind of trials have I made, with Cryftaline Glafy, 
with drops of fluid bodies, and feveral other ways,which do all feem to 
agree very exactly with this Theory. So that from this Principle well efta- 
blith’d, we may deduce feverall Corollaries not unworthy obfervation. 
_. And the firftis, that it plainly appears by this, that the production of 
__ the Rainbow is asmuch to be afcribed to the reflection of the concave 
~ furface of the air, as to the refraction of the Globular drops: this willbe . 
evidently manifeft by thefe Experiments, if you foliate that part of a 
Glafs-ball that isto reflect an drs, as inthe Cartefian Experiment, above © 
mention’d, the reflections will,be abundantly more ftrong, and the co- 
ours: more vivid ; and if that part of the furface be rouch d with Watet, 
{carce affords any fenfible colour at all, : 
Next we learn, that the great reafon why pellucid bodies beaten {mall 
are white, isfrom the multitude of refleCtions, not from the. particles of 
the body, but from the contiguous furface of the air. And this is evident+ 
ly manitefted, by filling the Interftitia of thofe: powder'd bodies with . 
Water, whereby their whitene& prefently difappears. From the fame 
reafon proceeds the whitenefs of many kinds of Sands, which inthe dMi- 
crofcope appear to be made up of a multitude of little pellucid. oale 
whole brighteft reflections may by the A“icrofcope be plainly perceiv 
to come from their internal furfaces; and much of the whinenae se ¥ Sy 
i oesigt by the affufion of fair Water to be contiguous to thole 
ces. 
The whitene& alfo of froth, is for the moft part to be afcribed to the 
: N 2 reflection 
