PTOLEMY. 
411 
mighty rivers, the Gir and Niger," he proceeds 
to describe the latter by his usual mathematical 
mode of enumeration. 
" And the Niger, which joins together the 
" mountains Mandrus and Thala. It also forms 
" the lake of Nigritia (Nigrites Palus), which 
" lies in lat. long 18°. 
" And has formed two derivations* to the 
" north, viz. to the mountains Sagapola and 
" Usurgala, — and one to the east upon the lake 
" of Libya (Libya Palus), which lies in lat. 35% 
" long. 16° 30'.'* 
Never, perhaps, has a more singular and unap- 
propriate description been given of a river, than 
this of its joining two mountains together. Pto- 
lemy seems evidently to have considered merely 
the geometrical line described by the river course 
across Africa, without viewing it as a body in 
motion. His description can be correct only on 
one supposition ; that of two rivers meeting in a 
common receptacle. With regard to the direc- 
tion of the streams, the only ground on which an 
inference can be made seems to be the following. 
* Htcr^cTroi, divertigia. It deserves notice, that this term, 
though it seems to convey an opposite idea, has merely the 
common signification of a tributary stream. Thus (Lib. iv. 
c. 16.) we have " divertigium ad Emodos montes, Fons vero 
" in lis," and similar instaaces in the same and other chapters. 
I 
