INTRODUCTION. xvii 



ments in favour of the identity of the Niger and Zaire were 

 probably instrumental in bringing about the present expe- 

 dition, in answer to this objection, has assumed the mo- 

 derate height of 3000 feet for the source of the Niger 

 above the surface of the ocean. This height, he observes, 

 would give to the declivity or slope of the bed of the river, 

 an average descent of nine inches in each mile throughout 

 the course of 4000 miles. Condamine," he adds, " has 

 calculated the descent of the Amazons at six inches and 

 three quarters per mile, in a straight line, which, allowing 

 for its windings, would be reduced, according to Major 

 Rennel's estimate, to about four inches a mile for the 

 slope of its bed." And this descent is not very different 

 from that of the bed of the Ganoes; it havino- been as- 

 certained from a section, taken by order of Mr. Hast- 

 ings, of sixty miles in length, parallel to a branch of the 

 Ganges, to have nine inches of descent in each mile in 

 a straight line, which, by the windings of the river was 

 reduced to four inches a mile, the same as the bed of 

 the Amazons: and this small descent gave a rate of mo- 

 tion to that stream somewhat less than three miles an 

 hour in the dry, and from five to six an hour in the Avet 

 season, but seven or eight under particular situations 

 and under certain circumstances. If then, the Ganges 

 and the Amazons flow at the rate of three miles in their 

 lowest, and six miles in their highest slate, with an average 

 descent of no more than four inches a mile, while the 

 Niger, according to the hypothesis, would have an average 

 descent of nine inches a mile, the objection to the great 

 length of its course in supposing its identity with the Zaire, 

 would seem to vanish. It has been sufficiently provec^ 



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