460 BURNING MIRRORS. 



that the ancle of incidence is equal to the angle of reflection ; and 

 having; shewn thai, in so just a position of the glass, th- sun's rayi 

 might h- re fleeted to the given place, ho observes that by means of 

 a number or gl isses reflecting the rays into the same focus, there 

 must arise at the given place the conflagration required, for inllam. 

 ing heat is the result of thus concentrating the sun's rajs : and that 

 when a body is thus set on fire, it 1: indies the air around it, so that 

 it comes to be acted upon by the two forces at once, that of the 

 sun, and that of the circumambient air, reciprocally augmenting 

 and increasing the heat ; whence", continues he, u it necessarily 

 results, that by a proper ^number of plain mirrors July disposed, 

 the sun's rays might be reflected in such quantity into a common 

 focus, at a bow. shot distance, as to set all in flames around it. At 

 to the manner of putting this in practice," he says, "it might be 

 done by employing many Jmmls to hold the mirrors in the de- 

 scribed position : but to avoid the confusion that might thence arise, 

 twenty.four rrirrors at least being requisite to communicate flame 

 at such distance, he fixes upon another method, that of a plain 

 hexagon mirror, accommodated on every side by lesser ones, ad. 

 hering to it by means of plates, bands, or hinges connecting them 

 mutually together, so as to be moved or fixed at pleasure in any 

 direction. Thus having adapted the large or middle mirror to the 

 rays of the sun, so as to point them to the given place, it will be 

 easy in the same manner to dispose the rest, so that all the rays 

 together may meet in the same focus ; and by multiplying com. 

 pound mirrors of this kind, and giving them all the same direction 

 there must thence infallibly result, to whatever degree of intense, 

 ness, the conflagration required at the place given. The better to 

 succeed in this enterprize, there should be in readiness," he adds, 

 " a considerable number of those compound mirrors to act all at 

 once, from four at least, to seven." He concludes his dissertation 

 with observing, u that all the authors who mention the burning 

 machine of the divine Archimedes, never speak of it as of one 

 compound mirror, but as a combination of many." So large and 

 accurate a description is more than sufficient to demonstrate the 

 possibility of a fact, so well attested in history, and by such a num- 

 ber of authors, that it would be the highest degree of arrogance 

 and conceit, to refuse our suffrage to such invincible testimony. 

 Vitellion, who lived about the thirteenth century, speaks of a work 

 of Anthemius of Tralles, who had composed a burning glass consist. 



