426 COSMOS. 



me, 225 have exhibited proofs of activity in modern times. 

 Previous statements of the number 32 of active volcanoes 

 have given sometimes about 30 and sometimes about 50 

 less, because they were prepared on different principles. 

 In the division made by me. I have confined myself to those 

 volcanoes which still emit vapours, or which have had 

 historically certain eruptions in the 19th or in the latter 

 half of the 18th century. There are doubtless instances 

 of the intermission of eruptions which extend over four 

 centuries and more, but these phenomena are of very rare 

 occurrence. We are acquainted with the lengthened series 

 of the eruptions of Vesuvius in the years 79, 203, 512, 652, 

 983, 1138, and 1500. Previous to the great eruption of 

 Epomeo on Ischia in the year 1302, we are acquainted only 

 with those which occurred in the 36th and 45th years before 

 our era, that is to say, 55 years before the eruption of 

 Vesuvius. 



Strabo, who died at the age of 90 under Tiberius (99 years 

 after the occupation of Vesuvius by Spartacus), and whom 

 no historical account of any former eruption had ever reached, 

 describes Vesuvius notwithstanding as an ancient and long 

 extinct volcano. " Above the places " (Herculaneum and 

 Pompeii), he says, "lies the Mount Vesuios, covered round 

 by the most beautiful farms, except on the summit. This is 

 indeed for the most part pretty smooth, but on the whole 

 chemical analyses made by Boussingault on gas-exhaling volcanoes of 

 the Andes (from Purace' and Tolima to the elevated plains of las Pastes 

 and Quito), both muriatic acid and sulphuretted hydrogen (hydrogene 

 sulf ureux) are wanting. 



32 The following numbers are given in older works as those of the 

 volcanoes still in a state of activity : by Werner, 193 ; by Caesar von 

 Leonhard, 187; by Arago, 175 (Astronomic Populaire, t. iii, p. 170); 

 variations which, as compared with my results, all show a difference 

 ranging from to T V in a downward direction, occasioned partly by 

 diversity of principle in judging of the igneous state of a volcano, and 

 partly by a deficiency of materials for forming a correct judgment. It 

 is well known, as I have previously remarked, and as we learn from 

 historical experience, that volcanoes which have been held to be extinct 

 have, after the lapse of very long periods, again become active, and 

 therefore the result, which I have obtained must be considered as 

 rather too low than too high. Leopold von Buch, in the supplement 

 to his masterly description of the Canary Isles, and Landgrebe, in 

 his Geography of Volcanoes, have not attempted to give any general 

 numerical result^ 



