THE SOURCE OF THE NILE. 



7 : 



near at hand exerts its natural influence upon the water, 

 which now is become light enough to be exhaled, though 

 it has ftill with it a mixture of the corrupted fluid, fo that it 

 rifes but a fmall height during the fir A few days of the in- 

 undation, then falls down and returns to the earth in plenti- 

 ful and abundant dews ; and that this is really fo, I am per- 

 fuaded from what I obferved myfelf at Cairo. 



My quadrant was placed on the flat roof, or terrafs, of a 

 gentleman's houfe where I was taking obfervations ; I 

 had gone down to fupper, and foon after returned, when 

 I found the brafs limb of the quadrant covered with 

 fmall drops of dew, which were turned to a perfect green, 

 or copperas colour; and this green had fo corroded the brafs 

 in an hour's time, that the marks remained on the limb 

 of the quadrant for fix months ; and the cavities made by 

 the corrofion were plainly difcernible through a micro- 

 fcope. . 



It is in February, March, or April only, that the plague 

 begins in Egypt. I do not believe it an endemial difeale, I ra- 

 ther think it comes from Conftantinople with merchandife, 

 or paffengers, and at this time of the year that the air ha- 

 ving attained a degree of putridity proper to receive it by 

 the long abfence of dews, the infection is thereto joined, and 

 continues to rage till the period I jull fpoke of, when it is 

 fuddenly flopped by the dews occafioned by a refrefhing mix- 

 ture of rain-water, which is poured out into the Nile at the 

 beginning of the inundation. . 



The firfl and moil remarkable fign of the change brought 

 about in the air is the fudden flopping of the plague a: 

 2 - Saint ' 



