548 Scientific News — Sitittigs of the Infiitute at Cairo. 



plode without light, however intenfe the heat, and vice verfd. — ^This part of the eflay, 

 where he examines the fource of light in the compofition of the body, and explains the 

 different modes by which the violent feparation is efFeded, as well as the confequences of 

 the explofion, appears highly ingenious. 



Such, Sir, is the outline of the paper which I think is mifunderftood and mifreprefented 

 by your correfpondent. The different parts can be only fairly appreciated by an examina- 

 tion of the fafts. This is a bufmefs to which I cannot now attend, and which is not fuited 

 to your Journal. Your giving me a little room for this analylls will oblige, Sir, 



Yours, 



A Constant Read&r. 



SCIENTIFIC NEWS AND ACCOUNTS OF BOOKS. 



Infiitute of Cair$. 



(Continued from page 5*3, vol. II-) 





H E fecond fitting was held on the nth Fruftidor, at feven in the morning, at which 

 Citizen Andreofly made a report on the fifth queftion propofed by Buonaparte. He ob- 

 ferved, in the firft place, that Egypt poflelfes no fulphur, but formerly imported it from Ve- 

 nice. The charcoal is obtained by burning the lupine in a trench, and afterwards fifting it. 

 The faltpetre is native, and is even faid to be found in veins (par veines) round Cairo. It 

 is refined in the fame manner as (commonly) in Europe. It is a true nitrate of potafli, and 

 not of lime, as in France. The boiling is made with the ftalks of Turkey-wheat, and it )• 

 purified with whites of eggs. The gunpowder is made by hand, and the workmen arc 

 naked. Each mortar contains fifteen pounds, and the procefs lafts feven hours. The 

 peftles weigh from nineteen to twenty-five paros. A fmall quantity of water is added, and 

 the granulation is performed by a fieve. The reporter affirms that this powder is very good\ 

 but that to render it ftill better it is neceflary that the proportions of France fliould be fol- 

 lowed. Two thoufand cantars (were) formerly made at Cairo, of which much was fent to 

 Leghorn. The beys had very little powder. Murat Bey had no more than 1,500 cantars. 

 It would be eafy, fays the reporter, to augment this fabrication, and even to export large 

 quantities to Europe- 



At the fame fitting, the citizen Monge read a memoir on the phenomenon, called le mirage 

 by French feamen, and by ours looming. This effe<Sl of refraftion was remarkably feen by the 

 French, in the courfe of their march through the defert. Villages feen at a diftance ap- 

 peared elevated, and as if built on an ifland in the middle of a lake. The furface of this 

 apparent water became narrower as they approached, until at length, when they were only 

 at a fmall diftance, it difappeared i but the fame illufion prefented itfelf, with regard to the 



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