Of Light and Colours.

*" e flected through the Pores of the Body,it becomes totally suffocated and lost

therein;

b (

Effects. Those made of reflecting Mirrours are moreP°Werful than those made with Lenses, (cater is par thus)e caufe the Rays from a Mirrour are reflected all toPoint nearly, whereas by a Lens they are refracted to'j'fferent Points, and are therefore not so dense or ar-® e stt. Also the whiter the Metal or Substance is, of^jhch the Mirrour is made, the stronger will be theand it is observable, that the great Mr. Boyle

j^ffect*ia

°Mng made a very large Mirrour of black Marble, itw °uld not so much aS set Wood on Fire, though ex-b°sed a long Time in the Focus, so small a Quantity

Rays are reflected from black Surfaces, the Reason.^ Which we shall hereafter explain.

8. Among a great Number of Mirrours made forbilr ning , melting , calcining , and vitrifying Bodies, that

Mr. IVilktte is worth our Notice ; it was 3 Feet 11ln °hes in Diameter, and its focal Distance was 3 Feet? Inches. The following Experiments were made with

by Dr. Harris and Dr. Defaguliers.

1. A red Piece of Roman Patera began to melt in 3",and was ready to drop in 100".

2. Another black Piece melted at' 4'and was readyto drop at 64/k

3 - Chalk taken out of an Echinus Spartagus, fledaway in 33".

4 - A Foffile Shell calcin’d in j".

5 - A Piece of Pompey’s Pillar at Alexandria vitrifiedin the black Part in 50", and in the white Part

,^ 54 '- ...

y Copper-Ore vitrified in 8".

?• Slag, or Cinder of ancient Irqn-Work, ready tofun in 29 k".

*• Iron-Ore fled at first, but melted in if'i

9 - Talc began to calcine at‘ 40", and held in theFocus 64".

10 - Calculus huntanus was calcined in 2'', and onlydropped off in 60".

D. A great Fish’s Tooth melted in 321"".

12. The