The exhibition of comprehensive volcanic collections brings to light the strong analogy subsisting between the trachytes belonging to volcanoes, far distant from one another, while it indicates the existence of great differences in the mineralogical composition of volcanoes situated very near each other. My most excellent friend and fellow-traveller in Siberia, Professor Gustavus Rose, recently subjected the trachytes of the Berlin Museum, the greater number of which were collected by myself, to careful crystallographical and chemical investigation. He found oligoclase and pyroxene on the trachytes of Chimborazo, Popocatepetl, Colima, Tunguragua, Puracé, Paramo de Ruiz, and the Peak of Teneriffe, which has recently been accurately examined by Mr. Charles Deville. The trachytes of Toluca, Orizaba, Gunung Barang, and Burung Agung, on the Island of Java, Argæus, in Asia Minor, Cuneguilla, south of Sta. Fé de Nuevo-Mexico, the Sièrra de San Francisco, west of the Rocky Mountains and Pueblo Zuni, consist of hornblende, oligoclase, and brown mica. The trachytes of Stromboli and Etna, those of the Siebengebirge (Drachenfels), and of Kara Hissar in Phrygia, consist of large crystals of glassy felspar, with numerous smaller crystals of oligoclase, some hornblende and mica. Oligoclase, having been mistaken for albite, led to the fantastic idea of a peculiar rock, the Andesite, prevailing in the Andes, and even led our great master, Leopold von Buch, to make some curious distinctions, (Déscription des Iles Canaries, 1836, pp. 186-87.)
To ascertain the average height above the level of the sea, I propose that furrows should be cut in the rocks of the different regions along with inscriptions, which might carry information to unborn ages, as has been done, on my suggestion, now some 25 years ago, by the Academy of Science at St. Petersburg, on the Caspian Sea, while Sir James Ross, in his "Voyage of Discovery in the Southern and Antarctic Regions," 1839-43, Vol. II. p. 23, regrets not having done so, or, at least, of having only once adopted this plan.
I would also, with all deference, suggest observations regarding the daily atmospheric variations or tides, so as to obtain tables of maxima and minima. In order to obtain these, whenever the frigate is at anchor near any coast, but particularly within the tropics, hourly observations with the barometer and thermometer (the latter affixed to the barometer, and also freely suspended in the open air), should be made through several consecutive days and nights. During the occurrence of an Aurora Borealis (or Australis), attention should be paid to the perturbations of the magnetic variation, and the magnetic intensity of the horizontal needle. Boreal Auroras have been seen in the southern latitudes of the Peruvian Pacific, as low down as 12° 13′ S.; but the occurrence of such phenomena there is of much less frequent occurrence than that of Austral Auroras in Scotland. It is important to keep an exact register of the intensity of blackness in the "coalbags," when the smallest stars surrounding them are still visible to the naked eye. The daily meteorological observations, as also those on the temperature of the sea, will probably be made on board ship, in conformity with the views of Lieutenant Maury, and the method agreed upon at the last nautical congress.
As I shall have long ceased to be numbered with the living, when the Novara returns to Trieste, richly freighted with scientific treasures of all kinds, with fresh information relating to organic and inorganic nature, to the races of man, their habits and languages, I now pray to Almighty God that His blessing may rest upon this great and noble enterprise, to the honour of our common German Fatherland! And concluding, in this night, these oblique, illegible lines, I remember, not without emotion, and with very mingled feelings, that joyous period of my life when, fifty-eight years ago, in the beautiful gardens of Schönbrunn, preparing myself for a long journey, I was enjoying with grateful mind the friendly kindness of the venerable Jacquin and Peter Frank.
A. v. HUMBOLDT.
Berlin, in the night of 7th April, 1857.