666. TRAVELS TO DISCOVER 
now begins to fill infenfibly, and contributes a large quan- 
tity of water to the Nile, before it falls down the catara& - 
of Alata. In the beginning of June, the fun having now 
paffed all Abyflinia, the rivers there are all full, and then is 
the time of the greateft rains in Abyffinia, while it is, for 
fome days, as it were, flationary in the tropic of Cancer. 
THESE rains are collected by the four great rivers in A- 
byffinia; the Mareb, the Bowiha, Tacazzé, 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 Egypt, were it not for the White Ri- 
ver, which, rifing in a country of almoft perpetual rain,. 
joins to it a never-failing flream, equal to the Nile itfelf.. 
In the firft 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 paffes clofe by that village, and after, through 
that wild and dreary.defert. The-fact is certain, and fure- ~ 
ly curious ; the caufe perhaps unknown, although it ct be: 
gueffed at.. 
I conczive, that moyntains are neceflary to occafion 
either rain or dew, by artefting and {topping the great quan- 
tity, 
