j5(j Lord Napier's different Contrivances 



mcnts, as well as to the accounts which have been trans- 

 mitted to us of the prodigious havoc which the engines of 

 Archimedes, some of which could not possibly act at any 

 great distance, made among the ships of the enemy *. Be 

 this as it may, the incredulity of so many modern philoso- 

 phers, some of them deservedly esteemed on other accounts, 

 naturally tended to discourage any attempts to verify the 

 performances ascribed to Archimedes and Proclus. The 

 surprizing effects of the concave reflectors of Tschirnhausen, 

 Vilette, Sir Isaac Newton and others, fall not under our 

 present consideration, as having been produced only at 

 small distances. At length, in 1726, M. du Fay found 

 that, " at 200, 300, and even as far as 600 French feet" 

 (about 640 English) , " the rays of the sun received on a 

 plane mirror, one foot square, and thence reflected to a 

 concave one 17 inches" (above IS English inches) " in di- 

 ameter, consumed combustible bodies in the focus of the 

 latter f." This interesting and literally brillianl experi- 

 ment no doubt had its influence in stimulating the active 



* See the antient authors quoted by bishop Wilkins in his Mathema- 

 tical Ma^^ic, book. i. chap. 17 j and by Dr. Hutton, in his Dictionary, 

 art. Afckimedes. 



t V. Mem. de 1' Acad. Roy. dcs Sc. An. 1746. Father Regnault ap- 

 pears to have str-ingely misunderstood this experiment of M. du Fay, 

 »' Encore qu.'lque pas," &c, " A few paces mort,'' (so that he, as well 

 jis Ozanam, seems still to have thought the distance at whicii Archimedes 

 burned the ships to have been greater than Kircher had given grounds to 

 believe it really was,) " A few paces more," says Ueunaulf, " and the 

 Stcrct of Archimedes is discovered or verified:" Pri j. torn. iii. Entre- 

 Uen iQ. The same suthor, in his Origine anr. de la Ffys.iwuv. (primed 

 1735), tpm. ii. p/ 233, has these words, " On yacon/i? que Us mirroirsy 

 &c. It is said that the mirrors of Proclus and Archimedes burned the 

 fleets of their enemies. With a plane glass and a concave mirrun' we now 

 Jinow how to e.xcite flame at 600 feet distance." Here would not the 

 reader be apt tfl conclude that the flame was excited, not in the focus of 

 ihe concave, between the two mirrors, which were 600 feet asunder, but 

 at that distance from the concave itself ? Certainly the secret of Archi- 

 Kicdes was far from bemg discovered by M. du Fay, who produced his 

 erl'cct by a double reflection ; whereas circumstances must have confined 

 Archimedes to a single reficciion j unless v.'C can believe that Marcellus 

 would allow him to fix his corxave to the ship he imended to burn, and 

 ro biincj some of the ropes, &c. into its focus. Saverien, in his Diction. 

 de Mtitb, a de Phys., article Miryjir, quotes Regnault't Physique, and 

 appears to have inadvertently followed his loose description, and even to 

 have made it still more ambiguous, M. du Fay's own account of his 

 experiment, inscited in the text, is quite plain and explicit Perhaps 

 Regnault's works are not much read ; but Saverein's Dictionary (printed 

 in 1753) is pretty generally referred to, It is a work ot mciit and uti- 

 lity, and therefcre its errors being the more likely to mislead careless 

 vcidcjrs, bl'.ould not pass u.^cyr^etti;d by those who observe them, 



mind 



