BURNING INSTRUMENTS. 



Instru- 

 ments. 



Lord Na- 



surmised, that Archimedes burned the Roman navie 

 with a portion of a section parabolical artificiallye made 

 to reflect and unite the sunnebeames a great distance 

 off, and for the construction of this glass toke great 

 peines,with high curiositie,to write large and many in- 

 tricate demonstrations, but it is a mere fantasie and ut- 

 terly impossible, with any one glass whatsoeuer it be, 

 to fire any thing only one thousand pace off, no though 

 it were an 100 foote oner, marry true it is the para- 

 bola for his small distance, most perfectly doth unite 

 beames, and most uehemently burneth of all other 

 reflecting glasses. But how by application of mo 

 glasses to extend this unitie or concourse of beames in 

 his full force, yea to augment and multiply the same, 

 that the farder it is carried the more violently it shall 

 pearse and burne. Hoc opus, hie labor est, wherein 

 God sparing life and the time which opportunitie 

 seruing, and minde to impart to my countrymen some 

 such secrets, as hath I suppose in this our age been 

 reuealed to very few, no lesse seruing for the securitie 

 and defence of our naturall countrey, than surely to 

 be mamailed at of strangers." 



A few years after the publication of the Pantome- 

 pier'sburn- tria of Leonhard Digges, our illustrious countryman 

 ingmirrors. Baron Napier of Merchiston, drew up a list of '* se- 

 cret inventions, profitable and necessary in these days 

 for the defence of this island, and withstanding of 

 strangers, enemies of God's truth and religion." 

 The first and second of these inventions are burning 

 mirrors, which Lord Napier has very briefly describ- 

 ed in the following words : 



First, " The invention, proof, and perfect demon- 

 stration, geometrical and algebraical, of a burning 

 mirror, which receiving of dispersed beams of the sun, 

 doth reflect the same beams altogether united, and 

 concurring precisely in one mathematical point, in 

 the which point most necessarily it engendereth fire ; 

 what an evident demonstration of their error who af- 

 firm this to be made a parabolic section. The use 

 of this invention serveth for the burning of the ene- 

 my's ships at whatsoever appointed distance." 



Secondly, ** The invention and sure demonstration 

 of another mirror, which receiving the dispersed 

 beams of any material fire, or flame, yieldeth also the 

 former effect, and serveth for the like use." 



It does not appear that Napier ever condescended 

 to give any farther account of these burning mirrors ; 

 for when he was solicited, a short time before his 

 death, by one of his most particular friends, " not to 

 bury such excellent inventions in the grave with him," 

 he replied, " that for the ruin and overthrow of man 

 there were too many devices already framed, which, 

 if he could make to be fewer, he would with all his 

 might endeavour to do ; and that therefore seeing the 

 malice and rancour rooted in the heart of mankind, 

 will not suffer them to diminish the number of them, 

 by any new conceit of his, they should never be in- 

 creased." 



The next burning mirror of which we have any 

 account, was invented by the learned Athanasius 

 Kircher. This indefatigable philosopher made a 

 great variety of experiments, for the purpose of esta- 

 blishing the authenticity of Archimedes's burning 

 mirrors. He began with combining a number of pa- 

 rabolic specula ; but this method was quickly aban- 

 doned, and he resorted to the use of plain mirrors. 



3 



Burnm* 



hist r 11- 



Ki relief's 



burning 



mirrors. 



Having procured a number of plain and circular glas- 

 ses, he placed them upon a wall, at such degrees of 

 inclination that they all reflected the light of the sun 

 to one point, and produced a considerable heat. His 

 principal experiments, however, were made with five 

 plane specula fixed in a frame, so that they collected 

 the solar rays at the distance of more than one hun- 

 dred feet. At this distance he produced a degree of 

 heat which sufficiently convinced him, that by increa- 

 sing the number of his mirrors, he could have consu- 

 med inflammable substances at a much greater distance. 

 He informs us in his Magica Catoptrica, that the heat 

 of the first reflection was different from that of di- 

 rect light ; that the light when doubled gave a very 

 perceptible increase of heat ; that it had the heat of 

 a fire when tripled ; that when quadrupled, the heat 

 could still be endured ; but that a fivefold reflection 

 made the heat almost intolerable. From these result; 

 he concludes, that a combination of plain mirrors wa& 

 capable of producing more powerful effects, than mir- 

 rors of a parabolic, hyperbolic, or elliptic form ; and 

 he entreats future mathematicians to prosecute the 

 subject with a more numerous combination of plane 

 specula. Not satisfied with these trials, Kircher, ac- 

 companied by his pupil Schottus, made a voyage to 

 Syracuse in order to examine the position of the hos- 

 tile fleet, and they were both completely convinced, 

 that the ships of Marcellus could not have been more 

 than thirty paces distant from Archimedes. 



The seventeenth century was distinguished by the vji ette 9 

 production of various burning mirrors, of different burning 

 constructions. The principal of these were made by mirror.-, 

 M. Vilette, a French artist at Lyons, who appears 

 to have constructed no fewer than five of considera- 

 ble magnitude. One of them was bought by M. 

 D'Alibert for 1500 livres : another was purchased 

 by Tavernier, and presented to the King of Persia : 

 a third was sent by the French king to the Royal 

 Academy : a fourth was bought by the King of Den - 

 mark; and the fifth was brought to England for pub- 

 lic exhibition. The first of these mirrors was thirty 

 inches in diameter, and weighed above a hundred 

 weight. Its focal length was about three feet, and 

 the size of the sun's image was about half a Louis 

 d'or. It was mounted on a circular frame of steel, 

 and could easily be put into any required position. 

 This mirror was made in 1670, and having been 

 brought to St Germains by the order of the king, his 

 majesty was so well pleased with it, that he rewarded 

 Vilette with a hundred pistoles for the sight of it, and 

 afterwards purchased it, and placed it in the royal 

 observatory atParis. The effects were the following : 



Seconds. 



A small piece of pot iron was melted in . . 40 

 A silver piece of fifteen pence was pierced in 24 

 A thick nail (le clou de paysan) melted in . 80 

 The end of a sword blade of Olii.de burnt in 43 



A brass counter was pierced in 6 



A piece of red copper was melted in ... 42 

 A piece of chamber quarrystone was vitrified in 45 



Watch-spring steel melted in 9 



A mineral stone, such as is used in harquebus- 



ses a'ronet, was calcined and vitrified in .1 

 A piece of mortar was vitrified in .... 52 

 Green wood and other bodies took fire instantly. 



The mirror of M. Vilette which was brought to 



