Of Light and Colours* 291

surface, and part is transmitted into the^ody, which is refracted in right Lines tol he second or lower Surface, where it isfgain partly reflected and in part refractedll Ro the Air, arid coming to the Eye, sen-ders the internal Parts of those BodiesVl fible, which for that Reason are said tohe diaphanous or transparent (CXV),

When

^■"irnents, has found that it is about 17 times less, orj a t the Density of the lunar Rays is to that of the so-ar as 3000000 to 1 ; wherefore a Burning-Glass must^ndenfe the Rays of the Moon near 3000000, t. e.f'tee Millions of times, to make them warm enough0 raise the Liquor of the common Thermometer ;j'hich is an Effect almost 200 times greater than Vil-cffe ’s Mirtour can produce.

^.(CXV) 1. The Opacity and Transparency of Bo^

* - in general is thus occasioned : Let AB be theSur-

of an opake Body A BCD, a Ray of Light GHj* htig thereon in the Point H will in part be reflectedn to the Ray H I, and by this reflected Ray the Pointjs .^comes visible to the Eye at I; and thus all they.'jittts, and consequently the whole Surface, is made1 ‘Me by that Part of the Light which it reflects.

2 - But the other Part of the Ray entering into thej t ^y, being irregularly refracted and reflected through

* sternal Substance of Particles and Pores, becomesf ‘ded, dissipated, absorbed and lost therein ; and there-p e as none of the Rays can come from the internal^ to the Eye, so none of those Parts can be visible,

d { he Body is in that cafe said to be opake.

In order to this we must consider, that though the5 te °' e Body be opake, yet the Particles of such a Body^ s,n g*y opake, but freely transmit the Light with-in teflectjng any Part between the Surfaces, and. arebefore in themselves transparent; and were thoseU 2 Particles

PlateXXXVI.Fig. 1.