CLIMATE. 
Ill 
in winter from 58° to 60° ; the difference between 
the greatest degrees of heat and cold seldom ex- 
ceeding thirty degrees of Fahrenheit's thermome- 
ter. On some occasions, however, it has been 
known to rise to 112°; but such an uncommon 
heat is generally of short continuance, and occurs 
most frequently in the Sahid.* At sunset the 
winds fall, the temperature of the air becomes 
cooler, and the superabundant humidity, which 
the heat exhaled, but could not elevate in the at- 
mosphere, is again desposited in the form of dew. 
As the evening descends, a thin mist veils the ho- 
rizon, and broods over the watery grounds, but in 
the darkness it becomes scarcely perceptible, and 
in the morning, when the sun rises, quickly dis- 
perses in flaky clouds. Nor are the clouds always 
dispelled by the action of the sun's rays ; for the 
atmosphere sometimes appears loaded, and exhi- 
bits all the meteorological symptoms which indi- 
cate rain in other climates, without any altera- 
tion of weather ensuing. The phenomena of the 
* The mean heat at Cairo, during the different months, is 
thus given, according to Reaumur's thermometer, by Cotte, 
an accurate meteorologist : number of observations in the day, 
three. January IP 0'— February W 9'— March 14° 5'— 
April 16° 5'— May 20° 5'— June 22^ 7'— July 23<^ 7'— August 
W 2'-— September 2P 6'— October 19*^ 4'— November 17° 4' 
—-December 12° 5' Mean heat of the year 17° 9'. — Jotir^ 
nal de Physique, July 1791. 
