THE SOURCE OF THE NILE. wy 
mear 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 {mall height during the firft 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, lam per-- 
fuaded from what L-obferved: myfelf at.Cairo... 
_ My quadrant was placed on‘the flat roof, or terrafs, of a 
gentleman’s houfe where 1 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. . 
Ir is in Fébruary, March, or April only, that the plague - 
begins in Egypt. I do not believe it an endemial difeafe, I ra-_ 
ther think it comes from. Conftantinople with merchandife, *. 
or paflengers, 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 juft fpoke of, when it is © 
faddenly ftopped 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. .. 
Tue firft and moft remarkable fign of the change brought: 
about in the air is the fudden ftopping of the plague. at. 
2 Saint.. 
