ILLUSTRATIONS (23). SOURCES OF THE NILE. 119 



combined results of the recent travels of Beke, Krapf, Isen- 

 berg, Russegger, Ruppel, Abbadie, and Werne, as ably and 

 comprehensively brought together in 1843 by Zimmermann. 

 " If a prolonged span of life," I wrote to him, " bring with it 

 many inconveniences to the individual himself, and some to 

 those about him, it yields a compensation in the mental enjoy- 

 ment, afforded by comparing the earlier state of our knowledge 

 with its more recent condition, and of seeing the growth and 

 development of many branches of science that had long con- 

 tinued torpid, or whose actual fruits hypercriticism may even 

 have attempted to set aside. This genial enjoyment has from 

 time to time fallen to our lot in our geographical studies, and 

 more especially in reference to those portions of which we 

 could hitherto only speak with a certain timid hesitation. 

 The internal configuration and articulation of a continent 

 depends in its leading characters on several plastic relations 

 which are usually among the latest to be elucidated. A new 

 and excellent work of our friend, Carl Zimmermann, on the 

 district of the Upper Nile and of the eastern portions of 

 Central Africa, has made me more vividly sensible of these 

 considerations. This new map indicates, in the clearest man- 

 ner, by means of a special mode of shading, all that still 

 remains unknown, and all that by the courage and per- 

 severance of travellers of all nations (among which our own 

 countrymen happily play an important part), has already 

 been disclosed to us. We may regard it as alike im- 

 portant and useful that the actual condition of our know- 

 ledge, should, at different periods, be graphically represented 

 by men well acquainted with the existing and often widely 

 scattered materials of knowledge, and who not merely de- 

 lineate and compile, but who know how to compare, select, 

 and, where it is practicable, test the routes of travellers by 

 astronomical determinations of place. Those who have con- 

 tributed as much to the general stock of knowledge as you 

 have done, have indeed an especial right to expect much, since 

 their combinations have greatly increased the number of con- 

 necting points ; yet I scarcely think that when, in the year 

 1822, you executed your great work on Africa, you could 

 have anticipated so many additions as we have received." It 

 must be admitted that, in some cases, we have only acquired 

 a knowledge of rivers, their direction, their branches, and 



