Scientific Reviews. 39 
tenance, to look upon this new head which has sprung from the 
dying hydra. Just at the period when men were calming into a 
confession of the necessity of further observation before an accu 
rate opinion could be formed, a fresh conjecture, without the sha- 
dow of a fact to support it, is thrust before the eyes of the public. 
It would be “ to cut the air with scimitars,’’ were we to do more 
than relate this choice specimen of induction ; and so delicate do 
we feel with respect to the precious production, that we would not 
even affect its entierty, but give it in the author’s words, were not 
its delivery somewhat too circumlocutory for our pages. 
The usual termination assigned to the Nile of Bornou, is in the 
sands of the desert of Bilmah, (Setzen ;) but our author considers 
that a mighty stream, such as he conceives “ the Nile of Bornou 
to be, when formed by the united streams of the Niger and Misse- 
lad,’ (the connecting branch being that communication which he 
supposes to exist between Lake Tchad and the Wad-el-Ghazel,) 
eannot be so disposed of in a sandy desart, (p. 58.) It appears to 
Sir Rufane that the desart of Bilmah is probably composed of sili- 
cious sand, (because the African wastes which he has traversed 
have been generally of that structure,) and silex not being an ab- 
sorbing substance, would permit the percolation of water, which 
might, ina subarenaceous stream, ‘‘ push on by the force of gravi- 
tation till it found its natural level.” ‘The level to which the 
Wad-el-Ghazel is supposed to be directed, is “ the sea, towards 
which all rivers tend in one way or another,” and that sea is the 
Mediterranean, the quicksands of the Syrtis being the precise place 
where the waters of the river are driven back and stopped by the 
sea on a low flat shore: “ they therefore having now no lower 
level to go to, form a plashy, moving quicksand, which extends to- 
wards the land as far as the level will admit, and is stopped only 
by the gradual rise of the ground,” (p. 61-2.) The reasons which 
have induced the author to this view are, lst, The Syrtis “is in the 
direct prolongation of the general course of the Nile of Bornou. 
2dly, It is the nearest point at which a river, disappearing where 
this river is said to disappear, in the desarts of Bilmah, could reach 
the sea.” -And 3dly, The occurrence of the ‘ Two Rivers’ near 
the rock Tibboo, in the very line between the Lake Domboo and 
the Syrtis, is the precise phenomenon which might be expected, 
according to this opinion, from the damming up of the hidden 
stream, (‘‘ by the ground rising in the vicinity of the Tiberti moun- 
tains,’) and its sinking again when the obstacle is surmounted, 
(p. 64.) Little thought De Mairan, when he calculated the eva- 
poration from the Mediterranean, with a view of disproving the 
necessity of an under current, that there might enter at an oppe- 
site point a stream almost as large as the Bosphorus, and which, 
spurning communion with the waters of the sea as with the sands 
of the desart, might possibly flow through the Straits of Gibraltar, 
itself a submarine current. 
Returning to the discussion of the geography of Ptolemy, the 
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