SB Russegger's Bemarks on the Climate of Egypt. 



than those of the day, yet the ease occurs but rarely of their 

 being imperceptible to sharp observation and with first-rate 

 instruments. 



Temperature. — The daily temperature of Lower Kgypt pre- 

 sents only two extremes, one maximum and one minimum ; the 

 former of which occurs between 2 and 3 p.m., and the latter 

 a short time before the rising of the sun. Egypt is among the 

 hottest of those countries of the globe which lie without the 

 tropics, but this applies properly only to Upper Egypt ; for 

 Lower Egypt, as a littoral tract, is too much exposed to the 

 cooling action of the sea-breeze not to have a diminished tem- 

 perature. In Alexandria and on the Delta the temperature 

 rarely attains 30° R. (99°.5 F.) ; but in Cairo, which is not 

 exposed to the sea-breeze, and has deserts on both sides, the 

 temperature is much higher, and often attains 30° R. and above 

 it, in the complete shade of a perfectly opaque body. The 

 mean temperature of Lower Egypt is between 17° and 18° R. 

 (70°.2— 72".5 F.). As at nightfall the wind is generally from 

 the north, the nights are perceptibly cool in comparison with 

 the temperature of the day, and there arise differences between 

 the temperature of tlie day and that of the night of from 10° 

 to 12° R. (22°.5 to 27° F.), which, it is true, are inconsider- 

 able when compared with the diflPerences of temperature of 

 night and day in the equatorial regions of Africa, but are very 

 great in comparison to the same phenomena in Europe. During 

 a prevalence of north winds, and the greatly diminished tem- 

 perature which accompanies them, and after a deposition of 

 dew, which appears more especially when the wind is north, 

 it often happens, particularly on the extensive plains of the 

 desert, that the thin covering of moisture which lies on the 

 surface in the morning becomes frozen, and thus we have 

 in a very simple way the phenomenon of the formation of 

 ice in the deserts of Africa. If in such a case the temperature 

 of the atmosphere be not so low as that a freezing of the dew 

 should be directly produced by it, yet this takes place in con- 

 sequence of the diminution of temperature in the liquid layer 

 and in the immediately adjoining air itself, and of the rapid 

 evaporation which results from the sudden change of tlie strata 

 of the air, caused by the prevailing north wind ; and thus we 

 wltne^ss tlie formation of ice, not only in the deserts of Egypt, 



