288

Of Light and Colours <

therein; and since none of those Raf®

come from the interior Parts to the E J e \

\}S

i

, 12. The Asbestos seem’d a little condensed in 28", 3sl!

Mr. Villette says, the Glass usually calcines it-

13. Marcasite of Gold broke to Pieces and began* melt in about 30".

14. A Silver Six-pence melted in 7T'. 1

15. A Copper Half-penny (of King William's ,) mehin 20", and ran with a Hole in 30".

16. A King George’s , ditto, melted in 16", and 1in 34".

17. Tin melted in 3".

18. Cast Iron melted in 16".

19. Slate melted in 3", and had a Hole in 6 ".

20. Thin Tile melted in 4"* had a Hole and ^vitrified in 80T

21. Bone calcined in 4", and was vitrified in 3 3 ' .

22. A Diamond weighing 4 Grains lost {- ot *-

W eight. ^

9. The Power of Burning* in Villette's Mirrour, n1 7be computed, and compared with the Heat of Wst® gFire, as follows : Since the focal Distance R X ' s 3 {Inches, and the Angle under which the Sun’s Ima£ e ^the Focus appears at R, is equal always to 3^ 0Degree ; therefore if we fay,

As Radius ■ —> — 90° 00^ —

IS the AnIlT 86111 ° f ] HRX = Q0 ° =

So is the focal Distance RX 3 38’ =:

To'the Semidiameter 1 ,

of the solar Spot 3 • 0,I 79

Whence 2 HX == 0,358 of an Inch, the Diame f/1 ^the solar Focus 5 but the Diameter of the Mirroui" ,v g47 Inches ; now 47 X 47 = 2209, and 0,358 *’ 3 ^= 0,128, &c. wherefore 2209 is to 0,128, as the Dfity of the Rays in the Focus to their common H enbut fc,i28) 2209 ( = 17257; which shews thatMirrour condensed the Rays Seventeen Thousand *Hundred and Fifty-seven times, ■

10 , 000 °°^7,667^

1,5^'

9,2

I