XX INTRODUCTION. 



prehend. In what way, it may be asked, can the tempera- 

 ture of a stream in 16° N. lat. affect the temperature of 

 the same stream in (f S. lal. ? There is no assignable ratio 

 in which it ought to encrease or decrease in its long course ; 

 it may change dail}-, and many times in the course of the 

 day according to the temperature of the surrounding at- 

 mosphere. Of the temperature of the Niger nothing is 

 known, for Park does not appear to have noticed it ; but 

 that of the Zaire was repeatedly ascertained, in the present 

 expedition, in different parts of its course, and was sel- 

 dom found to differ more than 2° of Fahrenheit either way, 

 from the temperature of the atmosphere ; remaining most 

 commonly about 76, and 77°, which was pretty nearly the 

 mean day temperature of the atmosphere. 



The hypothesis of Mr. Reichard, a German geographer 

 of some eminence, which makes the Niger to pour its 

 waters into the gulf of Benin, is entitled to very little atten- 

 tion. The data on Avhich it is grounded are all of them 

 wholly gratuitous. He proceeds on a calculation of the 

 quantity of water, evaporated from the surface of the lakes 

 of AVangara, and the quantity thrown into them by the 

 Niger, without knowing whether the Niger flows into 

 them or not, or even where Wangara is situated, much 

 less the extent and magnitude of those lakes. 'J'he Rio 

 del Rey, the Formosa, and the numerous intermediate 

 branches that open into the gulf of Benin, are supposed to 

 join in one great stream beyond the flat alluviil laud which 

 they seem to have formed ; the supposition, however, has 

 never been verified by observation ; but as far as it is 

 known, the Rio del Rey proceeds from the northward, and 



