398 COSMOS. 



counts of travels), is that, out af 407 volcanoes cited by me, 

 225 have exhibited proofs of activity in modern times. Pre- 

 vious statements of the number* of active volcanoes have 

 given sometimes about 30 and sometimes about 50 less, be- 

 cause they were prepared on diiFerent principles. In the di- 

 vision made by me, I have confined myself to those volcanoes 

 which still emit vapors, or which have had historically cer- 

 tain 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 ac- 

 quainted with the lengthened series of the eruptions of Ve- 

 suvius in the years 79, 203, 512, 652, 983, 11^8, and 1500. 

 Previous to the great eruption of Epomeo on Ischia, in the 

 year 1302, we are acquainted only with those which occurre'd 

 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 



(^Comptes rendus de VAcad. d. Sc, t. xliii., 185G, p. 746). Sartorius 

 von Waltershausen, on the other hand, observed on cones of eruption 

 of ^tna, in 1811, a strong smell of sulphureted hydrogen, where in 

 other years sulphurous acid only was perceived. Nor did Charles De- 

 ville discover any sulphureted hydrogen at Girgenti, or in the Maca- 

 lube, but a small portion of it on the eastern declivity of ^tna, in the 

 spring of Santa Venerina. It is remarkable that throughout the im- 

 portant series of chemical analyses made by Boussingault on gas-ex- 

 haling volcanoes of the Andes (from Purace and Tolima to the ele- 

 vated plains of Las Pastos and Quito) both muriatic acid and sulphuret- 

 ed hydrogen (hydrogene sulfureux) are wanting. 



* 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 {Astronomie Popidaire, t. iii., p. 170); 

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

 ranging from ^ to -J^ 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 ex- 

 tinct 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 nu- 

 merical result. 



