the Inflitute at Cairo. | 427 
by Bonaparte in the preceding fittmg. He firft obferved, that 
Egypt does not furnith fulphur, and that this article was 
formerly procured from Venice. The Commiffion were of 
opinion that it might be procured from Sicily. The chareoal 
employed in Egypt is from the lupine, which is: burnt-in 
trenches and afterwards fifted. The faltpetre is indigenous 3 
and it is even faid that veins of it are found in the neigh- 
bourhood-of Cairo: it is manufa€tured in the fame manner 
asin Europe. It is there in the ftate of a real nitrat of pot- 
ath, and not of lime, as in France : it is baked with the ftraw 
of Turkey corn, and purified with the white of an egg. Gun- 
powder is manufactured with the hand, and the workmen 
labour quite naked. Each mortar contains fifteen pounds, 
and it is pounded for feven hours. The peftles weigh from 
nineteen to twenty-five pounds each. The wages of the 
workmen are from twenty to twenty-five paras: they add 
water to it, and to granulate the powder it is fifted. This 
powder is excellent, and cheaper than that made in France. 
The inhabitants manufaétured 2000 cantars annually, a great 
deal of which was exported to Leghorn. The beys had very 
little powder. — Mourad- bey had no more than 1500 cantars. 
~ This manufactory might with care be eafily increafed, and 
confiderable quantities of gun-powder might be fent from 
Egypt to Europe. ; 
Cit. Monge read a memoir on that optical phenomenon 
called by the French failors mirage. , 
It often happens at fea, that a {hip feen at a diftance ap- 
pears as if painted in thgfky, and not to be fupported by the 
water. A fimilar effect was obferved by the Back in the 
courfe of their march through the Defert : the villages feem-at 
a diftance feemed to be built 6n an ifland in the middle of a 
lake. In proportion as they approached, the apparent fur- 
face of the water became narrower ; when they were oaly at 
a {mall diftance, it difappeared, and the fame illufion began, 
ip regard to the next village. C. Monge aieribes this effeét 
12 a diminutign of the denfity of the lower ftratum of the at. 
molphere. 
