124

BURNING MIRRORS.

feet and a half in diameter, which burnt at a distance offifteen or sixteen paces; of Villette and Tschirnhausen ;the now complete one of Euflbn; that of Trudaine, andalso that of Mr. Parker. M. Villette, a French artist, atLyons, constructed a large mirror, bought by Tavernier,and presented to the King of Persia ; another was boughtby the King of Denmark ; a third by the French king, andpresented to the Academy Royal; and a fourth was pub-licly exhibited in England. Dr. Desagliers and Dr. Harrisfound that this last produced the following effects on thesubstances subsequently mentioned:

A silver sixpence in 7" melted.

A halfpenny of George I. in 16" melted, and running witha hole in 34".

Tin in 3" melted.

Cast iron in 16" melted.

Slate in 3" fused.

A fossil shell in 7" calcined.

A piece of the Mack part of Pompey’s pillar, from Alex-andria, granite, in 50" vitrified.

The white part of ditto in 54" vitrified.

Copper ore in 8" melted.

Bone in 4" calcined.

The same substance in 35" vitrified.

An emerald melts into a substance like Turquoise stoneby its power.

A diamond, whose weight was eight grains, lost seven-eighths of its weight.

Asbestos vitrified, as all other bodies did, if kept longenough in its focus; but when once vitrified, heat has nofarther pow r er.

This mirror was 47 inches wide, and ground to a sphereof 76 inches radius; in substance a composition of tin,copper, and tin glass.— Phil. Trans, v. iv. p. 198.

Tschirnhausen ’s mirror comes next. These things are no-ticed of it in Acta Eruditorum for 1687, p. 52.

Green wood takes fire instantaneously, which ignition isnot destroyed by strong wind; water boils immediately;eggs boiled in it are perfectly edible; a mixture of tin andlead, three inches thick, dropped presently; iron or steelplates presently became red hot, and soon burnt into holes ;things incapable of melting soon became red hot like iron;slate first became white, then black glass; tiles convertedinto yellow glass; shells into a black yellow glass. Apumice-stone emitted from a volcano melted into whiteglass; a piece of a crucible vitrified in eight minutes;