Page:Travels to Discover the Source of the Nile - In the Years 1768, 1769, 1770, 1771, 1772, and 1773 volume 3.djvu/743

 THE SOURCE OF THE NILE.

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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 '