reaches to the knee,” and affords, I believe, the most ancient record in antiquity of snow within the tropics,[FD] as the Paropanisus is 12° lat. north of that limit. Zimmermann’s map of the district of the Upper Nile shows the dividing line where the basin of the great river terminates in the south-east, and which separates it from the domain of the rivers belonging to the Indian Ocean, viz.; from the Doara which empties itself north of Magadoxo; from the Teb on the amber coast of Ogda; from the Goschop whose abundant waters are derived from the confluence of the Gibu and the Zebi, and which must be distinguished from the Godjeb, rendered celebrated since 1839 by Antoine d’Abbadie, Beke, and the Missionary Krapf. In a letter to Carl Ritter I hailed with the most lively joy the appearance of the combined results of the recent travels of Beke, Krapf, Isenberg, Russegger, Rüppel, 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 enjoyment, 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 continued 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 manner, by means of a special mode of shading, all that still remains unknown, and all that by the courage and perseverance 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 important and useful that the actual condition of our knowledge, 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 delineate 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 contributed 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 connecting points; yet