physical powers had well nigh deserted me, and when I was surrounded by dangers and difficulties of no common nature, it was only by the recognition which I hoped for from him, that I had been encouraged to press onward with unalterable determination towards the goal which I had now reached. The emaciated figures of my Indians and faithful guides told more plainly than any words could do, what difficulties we had had to surmount, and had surmounted.” After expressions so kind towards myself, I must be permitted to subjoin the following passage, extracted from my Preface to the German Edition of Robert Schomburgk’s Account of his Travels, published in 1841. “Immediately after my return from Mexico, I notified the direction and the routes which should be followed to explore the unknown portion of the South American Continent between the sources of the Orinoco, the mountain chain of Pacaraima, and the sea-shore near Essequibo. These wishes, which I expressed so strongly in my Rélation Historique, have at last, after the lapse of almost half a century, been for the greater part fulfilled. Besides the joy of having lived to see so important an extension of our geographical knowledge, I have had that of seeing it attained by means of a courageous and well-conducted enterprise, requiring the most devoted perseverance, executed by a young man with whom I feel united by the double bond of similarity of pursuits and efforts, and of our common country. Motives such as these have alone been sufficient to overcome the distaste which I entertain, perhaps without reason, to introductory prefaces by another hand than that of the author of the work. But in this case I could not consent to forego the opportunity of expressing, thus publicly, my heartfelt esteem for the accomplished traveller who, in pursuit of an object deriving all its interest from the mind,--namely, in the self-imposed task of penetrating from East to West, from the Valley of the Essequibo to Esmeralda,--succeeded, after five years of efforts and of sufferings (which I can in part appreciate from my own experience), in reaching the goal which he had proposed to himself. Courage for the momentary execution of a hazardous action is more easily met with, and implies less of inward strength, than does the resolution to endure patiently long-continued physical sufferings, incurred in the pursuit of some deeply-felt mental interest, and still to determine to go forward, undismayed by the certainty of having to retrace the same painful route, and to support the same privations in returning with enfeebled powers. Serenity of mind, almost the first requisite for an undertaking in inhospitable regions, passionate love for some class of scientific labour, (be it in natural history, astronomy, hypsometrics, magnetism, or aught else,) and a pure feeling for the enjoyment which nature in her freedom is ready to impart, are elements which, when they meet