356 



GREEK SCIENCE. 



Zonaras. 

 A.C. 1160. 



Proclus. 

 A.C. 514. 



Tzetzes. 

 A.C. 1160. 



Napier. 

 A.C. 1596. 



Pappus, that Archimedes, by means of burning mirrors, set fire to the 

 Roman fleet that was drawn up to besiege Syracuse. This, however, 

 has been often denied. Descartes, and many after him, have regarded 

 the thing as impossible. To the discussion of this question we cannot 

 devote much space ; it will be expected, however, that we do not pass 

 it over in total silence. 



Father Kircher, although he was among the incredulous, in reference 

 to the Archimedean mirrors, concluded from an actual survey of the 

 site of the town and harbour of Syracuse, that the distance to which 

 the philosopher had to project the solar rays was not more than thirty 

 paces. And whatever may have been the doubts formerly entertained 

 on this subject, it is now well known, that the solar rays may, after 

 reflection, be thrown to an effective focus at a much greater distance 

 than this. Our deduction will not be speculative, but historical. 



Zonaras affirms, from the authorities above specified, that Archi- 

 medes set fire to the Roman fleet by means of the solar rays collected 

 and reflected by a polished mirror. He then adds, that Proclus, 

 copying his example, burnt with mirrors of brass the fleet of Vitalian, 

 who besieged Constantinople, under the emperor Anastasius, in the 

 year 514. 



Tzetzes, who also quotes the same authorities, presents a particular 

 explication of the mechanism of Archimedes' burning mirrors. " When 

 Marcellus (says he), had removed his fleet out of the reach of the 

 darts, Archimedes brought into play a hexagonal mirror, composed of 

 several other smaller mirrors, each of which had twenty-four angles, 

 and which could be moved by means of their hinges, and of certain 

 plates of metal. He placed this mirror in such a position that it was 

 in the midst of the meridional solar rays both in summer and in winter ; 

 so that those rays, being received on the mirror, were reflected by it, 

 and kindled such a fire as reduced the Roman vessels to ashes." This 

 is much such a description as might naturally be expected from a 

 person not skilled in either optics or mechanics ; and such a person was 

 Tzetzes. 



A very obscure hint, however, is sufficient to bring real genius into 

 action ; and it is highly probable, that the celebrated Napier, putting a 

 happy construction upon the words of Tzetzes, recovered the admir- 

 able invention of Archimedes. In a paper of Napier's, bearing date 

 June 2, 1596, and containing hints of secret inventions, we meet with 

 the following : 



" The invention, proof, and perfect demonstration, geometrical and 

 algebraical, of a burning mirror, which, receiving of dispersed beams of 

 the sun, doth reflex the same beams altogether united, and concurring 

 precisely in one mathematical point, in the which point most neces- 

 sarily it engendereth fire ; with an evident demonstration of their error, 

 who affirm this to be made a parabolic section. The use of this in- 

 vention serveth for the burning of the enemy's ships at whatsoever 

 appointed distance. 



