BURNING MIRRORS. 45Q 



tbe solar heat, that at last by encreasing the number of mirrors, he 

 coul I produce the ir.ost intense degree of it. 



Tzc'zes's description of the tjla^s Archimedes made use of, is 

 indeed very proper to raise such an idea as Kircber enter'ained. 

 That author .-ays, 'hat Archimedes set fire to Marceilus's navy, by 

 means ,jf n } >\\\ ningqlass composed of snmll square mirror*, moving 

 every way up.n ranges ; which, when placed in the sun's rays, di- 

 rected them upon the Roman fleet, so as to reduc* it to ashes at the 

 distance of a how. shot. It is probable Mr. J)e Bulfon availed him. 

 self of this description, in constructing his burning glass, composed 

 of 168 little plain mirrors, which produced so considerable a heat, 

 as to set wood in flame- at the distance of two hundred and nine 

 feet ; melt lead, at that of one hundred and twenty ; and silver, at 

 that of fifty. 



Another testimony occurs, which loaves not the least doubt in 

 this case, but resolves all in favour of Archimedes. Anthemuis 

 of Trall-s, in L> <lia, a celebrated architect, able sculptor, and 

 learned mathematician, who in the emperor Justinian's time built 

 the church of St. Sophia, at Constantinople, wro'e a small treatise 

 in Gre<-k, which is extant only in manuscript, intitled Mechanical 

 Paiadoxes. That work, among other things, has a chapter re- 

 specting burning glasses, where we meet with the most complete 

 descrpition of the requisites that Archimedes, according to this 

 author, must needs have been possessed of, to enable him to set fire 

 to the Roman fleet. He begins with this enquiry, *' How in any 

 given place, at a bow-shot's distance, a conflagration may be raised 

 by means of the sun's rays?" And immediately lays it down as 

 a first principle '' That the situation of the place must be such, 

 that the rays of the sun may be reflected upon it in an oblique, or 

 even opposite direction to that in which they came from the sun 

 itself." And he adds, " that the assigned distance being so very 

 considerable, it might appear at iir.-l impossible to effect this by 

 means of the reflection of the sun's rays ; but as the glory Archi. 

 modes had gained by thus setting tire to the Roman vessels, was a 

 fact universally agreed in, lie thought it reasonable to admit the 

 pos.'ihility of it, upon the principles he had laid down." He after- 

 wards advances farther, in this enquiry, establishing certain neces- 

 sary propositions in order to come at a solution of it. u To find 

 out therefore in what position a plain mirror should be placed to 

 carry the sun's rays by reflection to a given point, he demonstrates 



