OF RAIN. 125 



Mem. p. 157. 2 Phil. Tranf. Abr. 132. Plainly from the 

 following reafons : Thefe plains are entirely fandy, and, con- 

 fequently, emit, very little vapour, being foon parched by the 

 heat that there prevails ; confequently the intermixture of ma- 

 rine vapours can produce no effect. -Again, the clouds in 

 thefe trac"ts are elevated to a great height, and are attracted 

 by the electrical agency of the Cordellierres that border on 

 thefe plains, to their lofty fummits, and there produce copious 

 rains ; hence alfo the fandy and extenfive defarts of Arabia Arabia. 

 and Africa are feldom refreftied by rain. 2. It fcarce ever Africa, 

 rains in Egypt, particularly in Upper Egypt. Now it is to Egypt. 

 be obferved, that Egypt is fo fituated betwixt lofty mountains 

 that no wind can enter it without paffing over them, but the 

 northerly winds, which iffue from the Mediterranean ; for a 

 foutherly wind mull pafs over the mountains of Abyffinia ; an 

 eafterly, over thofe that intercede between the Red Sea and 

 the Nile, and proceeding from the Defarts of Arabia, can 

 convey little or no vapour ; and wefterly winds mull; pafs over 

 the Defarts of Africa and Mount Atlas. Now the northerly 

 wind does not begin to blow until the month of June, when 

 Egypt is fo fcorched as to emit fcarce any vapour, and the few 

 clouds it may convey are attracted by the mountains of Abyf- 

 finia. Towards the middle of June the inundation of the 

 Nile, it is true, commences, and then, as the northerly wind 

 Hill continues, perhaps rain might be expeded, but little at- 

 tention being paid to it then, we are not informed whether 

 any falls or not, perhaps the clouds then alfo pafs to the moun- 

 tains of Abyffinia, whither this wind conveys them, and which 

 they deluge with rain ; all other winds depofit their moifture 

 on the reverfe of the mountains they pafs over. 



Prognojlics of Ravi. 



When the barometer falls, and the hygrometer rifes, rain is Pmgnoftics of 

 announced. ram * 



When the barometer rifes, and the hygrometer falls, we may 

 expect fair weather, if farther changes do not appear in thefe 

 inftruments, as fometimes there fuddenly do. 



If the barometer falls and the hygrometer alfo, xvindy wea- 

 ther will probably follow — particularly if the barometer falls 

 much below its natural height, which in Dublin is from 29,9 

 , to 29,98, 



Again, 



