XI 



CHAP. XII. 



Of Burning Glasses. 



PAGJE 



1, 2. Introduction . . 70 



3, 4. Description of the glass Archimedes made use of 

 in setting fire to the Roman fleet, at the siege of 

 Syracuse . . 77 



5. The manner of using this glass 78 



6. A fleet destroyed by means of glasses, at the siege 



of Constantinople . .79 



7. Undoubted testimonies of the power of the glasses 80 



8. The ancients were well acquainted with the nature 



of refracting burning-glasses ib. 



CHAP. XIII. 



'-Of Universal Gravity, and Centripetal and Centri- 

 Jugal Force. Laws 'of the Movements of the 

 Planets, according to their Distance frojn the 

 common Centre. 



2. The moderns have demonstrated the laws of uni- 

 versal gravitation . . 82 



2, 3. The ancients were nst unacquainted with these 



laws . . . 82 83 



4. Of the soul of the world, which puts all nature in 



motion . . ib. 



3> 6. What retains the. heavenly bodies in their orbits 64. 



