( 6i] ) 
K Ifaac Newton ) fecundo fubjangit, quod ft lumen 
“ in tranfitu e vitro in aerem obliquius incidat , 
<c quam in angulo graduitm 40, illud in totum re - 
45 fleClitur. Ego vero relpondeo, quod ex iis, quae 
docui in Prop. 4. Cap. 1. elicitur hanc non effe 
veram luminis refledionem, fed potius novam Im- 
“ nier fi°nem ; & ideo nego quod ex iflo Phaenome- 
£ 110 fequatur lumen a partibus corporum folidis, 
“ alic l uo interjeao intervallo, refledi.” And a little 
lower, having quoted what Sir Ifaac Newton lays, 
concerning the blue Light, which, coming from one 
Prifm obliquely upon the farther Surface of another, 
is wholly reflected, at. the fame Inclination that the 
red Light is wholly tranfmitted. — He fays, “ Satis 
fit iterura refpondere, quod in hoc ctiam cafu eft 
“ nova luminis immerfio, quae dicitur ab audore 
“ refledio. 
But this is only cavilling about Words ; for if the 
Ray of Light, which moving in a denfe Medium 
fails obliquely on the Surface common to that and a 
rarer Medium, be turned back again in the denfe 
Medium, fo as to make the Angle in which it returns 
from the laid Surface equal to that in which it came 
to it ; this Return of the Ray may properly be call- 
ed a Reflection) whether the Ray be turned back at 
the Point of the Incidence in the Surface, or be car- 
ried about the Point of Incidence in a fmall Curve 
whole Confideration may be omitted in tracing the 
Way of a Ray of Light in its PafTage, for making of 
optical Machines. Whoever reads the 8th Prop? of 
the id Part, Book II. of Sir Ifaac sOpticks, may very 
eafily find that he was not ignorant of the turning 
back of the Ray under the Surface of the Glafs be" 
fore 
