66ti TRAVELS TO DISCOVER
now begins to fill infenfibly, and contributes a large quan- tity of water to the Nile, before it falls down the cataract of Alata. In the beginning of June, the fun having now pafled all Abyffinia, the rivers there are all full, and then is the time of the greateft rains in Abyffinia, while it is for ibme days, as it were, flationary in the tropic of Cancer.
These rains are collected by the four great rivers in A- byffinia; theMareb, the Bowiha,Tacazzc, and the Nile. All thefe principal, and their tributary ftreams, would, how- ever, be abforbed, nor be able to pafs the burning deferts, or find their way into igypt, were it not for the White Ri- ver, which, riling in a country of almoft perpetual rain, joins to it a never- failing ftream, equal to- the Nile itfelf.
In the firfl days of May, the fun, in his way to the northern tropic, is vertical over the fmall village of Gerri, the limit of the tropical rains. Not all the influence of the fun, which has already paft its zenith, and for many days has been as it were ftationary within a few degrees of it over Syene, in the tropic of Cancer, can bring them one inch far- ther to the northward, neither do any dews fall there as might be reafonably expected from the quantity of frefh and exhalable water that is then running in the Nile, though it pafTes clofe by that village, and after, through that wild and dreary defert. The fac~t is certain, and fure- ly curious ; the caufe perhaps unknown, although it may be gueffed at.
I conceive, that mountains are neceffary to occafion either rain or dew, by airefting and flopping the great quan- tity
