Altogether, I calculate the number of active volcanoes on the surface of the earth to be upwards of 225--one-third of which, or 75, are upon the various continents, and the remainder upon the insular world. The Western Continent has 53 active volcanoes--of which, North-Western America, north of the river Gila, has 5; Mexico, 4; Central America, 18; South America about 26. Viewing the globe as a whole, there presents itself an extensive oblique region in which volcanoes most abound, stretching from S.E. to N.W. in the more westerly part of the Pacific, between 75° W. and 125° E. of Paris, and between 47° S. and 66° N. In this region, the fused elements of the interior of our earth may be said to be most permanently in communication with the atmosphere. The greatest attention should be paid, with the view of improving them, to the sections and maps of Chili, contained in the work, "Buenos Ayres and the Provinces of Rio de la Plata," published in 1852 by Sir Woodbine Parish, and still more so, to that entitled "Map of the Republic of Chili, compiled from the Surveys of Gilliss, Pissis, Allen, Campbell, and Claude Gay, between 23° and 44° S., as contained in Gilliss' 'United States Astronomical Expedition, 1847-52 Washington, 1855.'" The chief object to be aimed at by the _Novara_, with respect to scientific enquiry, seems to me to be the formation of a collection in the Geological Institute of Vienna, in comparison to which all the collections which at present aspire to be considered rich in volcanic specimens, (such as those of Berlin, Paris and London), should appear to be insignificant. In all periods of history, travellers are only the representatives of the state of knowledge of their own time, and consequently, collections always present the readiest means of promulgating new discoveries by oryctognostical examination or chemical analysis. In order to set on foot a grand Volcanic Museum, it would be necessary to bring home from every one of the volcanoes visited, not less than 10 or 12, but still better 15 or 18, specimens of the porphyritic trachytes, all carefully selected, well-shaped, containing crystals not disintegrated, and of sufficient size to admit of a fresh fracture being made. For such quantities, however, there cannot be provided on board ship, even with the kindest patronage of the commanding officer, sufficient space for the accumulations of two years' arduous efforts in forming a collection. The greatest part, therefore, should be sent by other conveyance to Trieste, the most secure channel being through the consuls of the Austrian Empire, or those of allied powers, or through the medium of British, Dutch or American mercantile establishments, or by the regular packets.