THE ISTHMUS OF DARIEN. The following interesting letter from Baron Alexander Von Humboldt to Lionel Gisborne, Esq., M.A., C. E. has been made public:— “Sir—I trust you will excuse the oldest among the travellers in both the tropics of America and the steppes of Siberia, for having so long delayed to thank you for the information I derived from your interesting journal, &c., on the junction of the Atlantic with the Pacific. The position I occupy in this country and the ardent desire I feel to finish, before my death, some sientific works which I had the imprudence to begin, considerably interrupt the even course of my correspondence. I therefore hope that I shall meet, on your part also, with that indulgence which your countrymen have shown me during so long a period. “I have not been beyond the Rio Rimo, which lies east of the mouth of the Atrato, since the time when I left the island of Cuba on my way to Lima by Bogota, Quito, and the river Amazon, for the purpose of observing the passage of Mercury through the solar disc. I was then on friendly terms with a very intelligent merchant, Don Ignacio Iombo, of Cartagena, in America, and I recollect that the Casso (Treasury convoy) of Guayaquil was then on its way to Europe, by the road from Cupica to the Atrato, which was first opened by the Biscayan pilot Poguerache. Knowing, geologically, the interruption of the mountain chains, and the depression of the range in the eastern part of the Isthmus, my attention has remained fixed during this last half century on the Bay of San Miguel and the route from Cupica to the Rio Napipi. Owing to my friendly relations with General Bolivar, I obtained through him the first line of levels across the Isthmus of Panama. Ever since the subject has not ceased to occupy my mind, as the various works and maps which I published since 1810 and my correspondence with various statesmen will testify. But all my striving and urging only led to imperfect trials and projects calculated for a line to the west of the meridian of Panama and Portobello, none of which ever gained my confidence. I had, however, the gratification of seeing my views honoured by an eminent member of Her Britannic Majesty’s navy, Captain Fitzroy. (Journal of the Royal Geographical Society, vol. xx., p. 20.) “The increase of human knwledge, and the immense progress of science, arts, and industry among the western nations, have given us powers which only call for application. Everything depends upon energy and perseverance. I therefore congratulate you, Sir, and your courageous friend, Dr. Cullen, as well as Sir Charles Fox, Mr. Henderson, and Mr. Brassey, for having given your names to so noble an undertaking. I have always considered, firstly, the opening of an oceanic canal, without locks; and secondly, the cut at Huchuecoca, in the valley of Mexico (which is on a comparatively smaller scale, as may be seen by the map and section I published), as two events calculated highly to improve the relations between the different families of the human species. In fact, such a work as the one you contemplate will bring Eastern Asia nearer to the nations of Europe and America. It will render the whole globe more easy to be travelled over—this little globe, of which Christopher Columbus, in one of his letters to the Queen of Spain, said, ‘el mundo es poco.’ It will facilitate the diffusion of productions, especially of precious metals, of which the relative value (1 to 15 5-6ths) would change too suddenly without this ‘permeability’ of the world. “As early as the discovery of the new Continent, civilisation had spread, in a direction from north to south, over those portions of America which he opposite to Asia, those on the European side being then occupied by barharous hunting tribes. The finest harbours, the most precious products, are likewise found in the West. Even the currents of the air, by their direction, contribute towards the preponderance of West American power over the rich countries of Asia. The increasing importance of the west coast of America promises to balance, at some future time, the surprising progress of the Atlantic States, provided the western States keep themselves free from that hideous disease—slavery of coloured people. “Indeed, Sir, I feel the most ardent wishes for the happy suceess of this oceanic canal. The attention which the public of the two continents bestows already upon your undertaking will increase, as soon as you are enabled, assisted by further explorations, and a survey extending over all details, and carried on by a great number of experienced men, to publish, on a large scale, maps and sections of the line fixed upon between Puerto Escoces and the Gulf of San Miguel. The changes which the success of your undertaking is sure to effect in the international commerce of the world will only disturb such people as in the narrowness of their viewa oppose themselves to the natural and providential course of events, and shed tears over the unfortunate discovery of America. The Rio Huaxacualco with its portage to the Rio Chimalapa (Tchuantepee), of which I published the first map after the itineraries discovered by me in the archives of the vice-kingdom of Mexico, will always be of great importance, owing to its position opposite Louisiana, in the Gulf of Mexico, which has all the appearance of soon becoming a mare clausuma lake of the United States. The nature of the soil, however, does not allow great works to be carried out in that locality; besides, you know the difficulties impeding any canalization or rectification of rivers of great length, and the great variations of the volume of water, as in the river San Juan; but a radway would be a great advantage to the southern States. “The great interest which every one at the present time takes in the canalization of the Isthmua recalls a similar fact to my memory, reminding me of the sudden interest created by the discovery of guano. “I was the first who brought guano to Europe, of which Klaproth and Vauquelin published an analysis. During 40 years I preached, but always in vain, the usefulness of this substance, and in vain did I recommend its employment in fertilising the fields of Europe. But it is only 15 or 18 years since it has at last become a great article of commerce. “I beg of you, my dear Sir, to present my kind remembrance to the excellent and able Mr. Peterman, &c. “Alexander Von Humboldt. “P.S. I am not surprised at the difference between the level you found at Turbaco and my own statement. To this, however, I had prudently added, ‘doubtful barometrical observation.’ (See my Recueil d’Obsercations Astronomiques et de Mesures Barometriques, vol. i. p. 299.) The fact that the gas issuing from the little volcanoes at Turbaco is inflammable in its natural state has already been communicated by Colonel Acosta (Journal, p. 65). It appears that the gaseons fluid which issues from the ‘salses’ is not the same at all times. I find in my journal that, in 1801, the flame of any burning substance was suddenly extinguished on being thrown into a bottle containing air from those little volcanoes. “Parrot, also, in the mud volcanoes in the island of Taman, found only azote, although the gas emitted would burn at other times. (See my Relation Historique, vol. xii., chap. 29, p. 367 371).”