BURNING GLASS OF ARCHIMEDES. SIT 



slightly boiled five parts of phosphorus with one of pure 

 soda in rectified alcohol, I poured this liquid still hot into a 

 solution of crystals of nitrate of lead in water. The pre- 

 cipitate I remoYed from one piece of filtering paper to an- 

 other, so as to deprive it quickly of its moisture, without 

 allowing the oxigen of' the air to act on it*. In this state 

 it was of a dark colour, and possessed all the properties 

 mentioned in § 5 ; but it had likewise that of detonating 

 briskly, when the smallest quantity folded in paper was 

 struck with a hammer. When the paper was opened after 

 the experiment, I found it coated with lead completely re- 

 vived. I also found, that touching it with a drop of sul- 

 phuric acid was sufficient to set it on fire. 



X. 



Report made to the Physical and Mathematical Class of 

 the French Institute on a Burning Mirror prese^ited to 

 the Class by Mr, Peyrard +. 



M 



R. PEYRARD, who has just published an elegant Bumin? glass 

 translation of the Works of Archimedes, was naturally led °^'^'^*^^'™®^^' 

 to reflect on the means, which that great geometrician is said 

 to have employed, to burn the fleet of Marcellus before Sy- 

 racuse. Both the ancients, and the authors of the middle 

 age relate, that he used a burning mirror; but none of 

 them enter into the particulars sufficiently, to gives us an 

 accurate idea of his process. Anthemius, who built the 

 church of Saint Sophia at Constantinople in the sixteenth 

 century, and appears to have been a very intelligent archi- 

 tect invented an assemblage of plane mirrors, to produce 

 the same eSect as that of Archimedes. Since that time 

 Kircher, who perhaps was unacquainted with the worlcs of 

 Archimedes, thought of something similar. Lastly Count 

 de Buffon constructed a burning mirror, composed of a 

 hundred and sixty eight plane glasses ; and the experiments. 



* The temperature that day was 13° K. (66« F 

 t Sonnini's Bibliotheque Physico-economique, 



F.). 



Nov. 1807, p. 

 349. 



