LARGE BURNING LENS, gn 



of ammonia: after which I sought in vain to detect man- 

 ganese, lime, or any other substance, in the filtered liquor. 



This mineral is consequently a pure oxide of iron crystal- A pureoxida 

 lized in cul)es ; and accordi^ig to my last researches it con- ° "^'^' 

 sists of 705 iron with 29'5 oxigen. 



VI. 



Extract of a Letter from Mr. Coutelle, Suhinspecfor at 

 Reviews, to Mr. Guyton-Morveau, on the Parabolic 

 Lens of Rospini, purchased al Vienna for the French Go' 

 vernment*. 



T, 



HIS lens is about a metre [3 feet 3 in.] in diameter, and Large burning 

 2| met. [S f. 4 in.] focus. It is composed of two pieces of ^'^"^' 

 glass, united together by a hooj) of iron, so as to form a 

 hollow vessel capable of holding SO or 90 quarts of spii-it of 

 wine. 



It was made at Gratz, in Styria, by Rospini, a celebrated made foe some 

 mechanist, for some alchemists. It was not cast, but soften- alchemists, 

 ed by heat, and bent over a parabolic mould. Several 

 pief es were broken before he succeeded, so that it cost 

 ori'jinally 20 or 30 thousand francs [from 800 to 1200 gui- 

 neas]. Mr. Coutelle paid for it 290O florins [£338] in 

 paper money. 



Mr. Jacquin of Vienna, and sereral men of science, who its effects. 

 were witnesses to the experiments, say, that it burned a dia- 

 mond in a few seconds, and fused platina in a few minutes. 

 A button of platina weighing 29 grains was melted by it, 

 and made in part to boil. The diameter of the focus does 

 not appear to exceed four lines. 



The lens, with the apparatus for placing the object of j^j^^^ ^^ ^^^^ 

 the experiment, fixed on a platform, and placed on an in- with the sun. 

 clined plane mounted on a strong frame, is made to follow 

 the coarse of the sun by means of machinery regulated by 

 a pendulum beating seconds. 



Wheu made to incline to.vard the east or west it requires 

 a counterpose, otherwise it would be liable to fall, being of 

 the weight of 250 kilogr. [550 lbs avoird.]. 



* Abridged from the Aanales de Ghimie, vol. LXIX, p. 92. 



H2 VII. 



