THE SOURCE OF THE NILE. 66;
tity of vapour which is here driven foiuhward before the Etefian winds. Novv,allthat country between Gerri and Syene is flat and defert,fo that this interruption is wanting; and it is owing to the famecaufe, that the bounds of the tropical rains do flop farther to the fouthward as you travel weftward, and in place of lat i6°, which is their limits at Gerri, they are con- fined within lat. 14 in that part of the kingdom of Sennaar which lies fouth and weft of that capital, where all is free from mountains till you come to thofe of Kuara and Fa- zuclo.
Yet although the fun's influence when at its greateft, is not ftrong enough to draw the boundaries of the fummer's rain farther north than Gerri, all the time that it is in the tropic of Cancer at its greateft diftance, thefe rains are then at their heavieft throughout all Abyflinia ; and Egypt,andall its labours, would foon be fweptinto the Mediterranean did not the fun now begin to change its fphereof a&ion by ha- ilening its progrefs fouthward.
From Syene the fun pafles over the defert, and arrives at Gerri'; here he reverfes the eflfe&s his influence had when on his paflage northward ; for whereas, in his whole courfe of declination northward, from the Line to Gerri, he brought on the rains at every place where he became vertical, fo now he cuts off thofe rains the inftant he returns to the zenith of each of thofe places pafling over Abyflinia in his journey fouthward, till arrived at the Line, in the autumnal equinox, his influence ceafes on the fide of Abyflinia, and goes to extend itfelf to the fouthern hemifphere. And fo precifely is this ftupendous operation calculated, that, on the 25th of September, only three days after the equinox,the
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