Of Light and Colours.

can see nothing of the internal Sub-stance of such a Body, which therefore isstrict to be opake.

But

lo. Since "Rays but 35 times denser than in their na-tural State with us, have a Power of Burning equal to^ood-Fire, if we divide 17257 by 35, the Quotienthull be 493 ; therefore such a Mirrour will burn withM Intensity of Heat 493 times greater than common'•re. No wonder then that Bodies which remain un-^ter’d by the Force of our greatest common Fires (asjhat of a Glass-House, where Gold has been found tod e several Days in Fusion, without any sensible Loss ofWeight) should immediately become fused, fume away'h part, part be dissipated and driven away in large Par-oles, and part remain in the Form of a Caput Mor-i’tuiti ; all which Phænomena have been observed of 1p°ld in the Focus of a large Burning-Glass. Andhow rudely such a Glass would treat the Principles ofChymijis, and what Confusion it would induce inyieir Arithmetic of Elements, they will be better cer-sisied of, when they shall attempt to analyse Nature,reduce Substances to their original Principles, by^Qre active and effectual Means than Laboratories atHesent afford.

v. 1 1. Notwithstanding the prodigious Density of the. a ys in the Focus of those large Burning Glasies, yet!* has been always observed, that the Rays reflected toJ,? by the Moon when at Full, and concentered in the. °c us 0 f those Glasses, produce no Heat that is sensiblethe least Degree, as is demonstrated by holding. af 1r -rmometer in the Focus of lunar Rays, which al-remains without the least Appearance of Motion,he Reason of this will appear by the following Cal-Ration.

o Let ABD be the Earth, C its Centre, MOj, e Moon, N the Centre, N e the Semidiameter of theo °°n, which is equal to 1087,5 Englisn Miles; thee !)ddiameter of the Earth. D C — 4000 Miles; theFtzj,. l[_ U Distances

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