36_ Account of a Journey to the 



to be ascribed to one and the same period ? I am inclined 

 to think it is but in conscqiieuce of probabilities deduced 

 from all the tacts which relate to that grand epoch. 



I shall not speak in detail of all those observations which 

 cannot appear insulated ; such as the existence of obsidian 

 stone and petro-silcx in currents, the incontestable transi- 

 tion of obsidian stone to pumice stone, &c. My position 

 was too favourable not to take advantage of it in every man- 

 ner possible. I rectified by the compass the large chart 

 published by Lopes ; and I several times repeated the only 

 experiment I could make on the magnetic needle, namely, 

 that on its inclination I always found it more than five de- 

 grees tow-ards the south pole. At the height at which I was 

 placed, the solar rays had not yet traversed two-thirds (in 

 weight) of the atmosphere. I shall add some remarks to 

 those I have already made on the origin and distribution of 

 free heat in the atmosphere, in regard to the intensity of the 

 rays, the density of the strata, and the height above the 

 earth. 



The puffs of vapour which warmed me from time to 

 time, at length attracted me into the crater. One can de- 

 scend into it only by three indentations : its edges are per- 

 fectly steep in the inside, and highest towards the north : 

 it is of an elliptic form, and may be about 1200 feet in 

 circumference and 110 in depth. Proceeding from the steep 

 edges, the declivities consist of a snow-white earth, which 

 Ibrms a contrast with the beautiful orango colour and the 

 bright splendour of the crystals of the sulphur w hich cover 

 all the still solid masses. This earth results from the de- 

 composition of tlic blackest and hardest vitreous and por- 

 phyritic lava: it is continually softened by a very hot mois- 

 ture : one therefore glides rather than descends to the bot- 

 lojn of the crater. The whole, hovvev^er, is solid ; and the 

 lowest part is occupied by blocks, which crumble dow n from 

 the steep edges according as these matters are decomposed, 

 and sink into the interior of the gulf. 



, The vapours, which issued in abundance from among 

 these blocks and an infinite number of crevices, certainly 

 came from, the depth of several leagues, and retained a great 

 intensity of "heat. . The thermometer exposed in a crevice 

 speedily rose to 80. degrees, and no doubt would have risen 

 higher had the tube been longer. To my great astonish- 

 ment, I found that this scorching vapour was composed 

 only of sulpluT and water perfectly insipid. I searched, but 

 in vain, for traces of sulphureous acid, soda, and hydrogpn 



gas. 



