for the Defence of this Island, sf 



mind of Buffon to attempt th^ production of fire by c.-'j 

 reflection only. But, as he himself intimates, he ■.■,-.$ 

 chiefly prompted to make this trial by a passage in the thi'. i 

 part of the Magia Caioptrlca of Kircher*, \\iio says, £;;>.■» 

 certe hiijus rei, Sec. '^ I certainly made trial of this ma.tcr 

 with five plane specula. The heat, at the first reflection, 

 was different from that of direct light. The light when 

 doubled gave a very perceptible increase of heat ; when tri- 

 pled, it had the heat of a fire ; when quadrupled, the heat 

 could still be endured ; but a live-fold light made the heat 

 almost intolerable." Hence he concludes that a numerous 

 combination of plane mirrors, which should reflect the sun's 

 light to the same point, would produce much greater effects 

 than any parabolic, hvperbolic, or elliptic burning mirror. 

 This, he says, he is warranted to affirm, from experiments 

 he made with his five plane specula, at the distance of 100 

 feet and upwards. And he earnestly entreats mathemati- 

 cians to pursue this object with their utmost diligence, 

 Kircher was born in 16OI f, five years after the date of 

 Napier's memoir. It is generally said that his experiments 

 were sugo-csted by the hints of Tzctzes ; and, no doubt, 

 would be encourag-ed by his finding, on *' diligent exa- 

 mination" of the spot in 1636, that " the combustion said 

 to have been kindled by Archimedes was possible, and that 

 the caustic line was but about 30 paces," or about I60 

 English feet. Thus the count de Buffon had only ty fMit 

 in execution the directions of Kircher X, which he did, ia 

 March and April 1747, with great perseverance, ingenuity, 

 and expense. After various trials, with combinations of 

 different numbers of plane mirrors, the greatest consisting 

 of 400, placed in a square frame and brought to bear upon 

 the object by means of screws, he succeeded in melting 

 lead and tin at the distance of about 50 English yards ; and 

 in burning lighter substances, at the distance of 75 yards. 

 With summer heat, and a better apparatus, he expresses a 

 certainty of producing combustion even so far as 400 Frendl 

 feet, equal to 142 of our yards, and perhaps further §. This# 

 if Kircher's admeasurement was right, may be reckoned Jtt' 

 least double the distance at which Archimedes produced hU 

 conflagration j and thus he and Buffon together have at last 



'* Quoted by Paulian in his valuable Diction, de Fhjsiqiie, article Ca- 

 tojU'i'iuc. 



t Stc Hnttoti's Dictionary, article Kinher. 



X Paulim's Dictionary, article Cnsicl. 



5 Sec litt Mr:m. de l Acad des S'ienrc^, an 1747; Dirtio"- d.^ Piyyt, 

 df Pauluvi,Mi.Ca(ol'hific\ and Hmiou'!. Dictionary, art. Baming C!/iV.<. 



convinced 



