NOME II. VESICULAR LAVA. 365 



far at least as we can judge from his own words. 

 fc I did not perceive, as several travellers have 

 asserted, that the air here is so thin and rarefied 

 as to prevent, or at least greatly incommode, 

 respiration." Mr. Brydone has said nothing on 

 the subject, and his silence may induce us to 

 conclude that he experienced no difficulty. 



" I, my servant, and the two guides, suffered 

 no inconvenience from the air. The exertions 

 we had made, indeed, in climbing up the craggy 

 steep declivities which surround the crater, pro- 

 duced a shortness of breathing ; but when we 

 had reached the summit, and recovered from our 

 weariness by rest, we felt no kind of inconve- 

 nience, either while sitting, or when, incited by 

 curiosity, we went round and examined different 

 parts of the edges of the crater. The same is 

 affirmed by Borelli : JEque bene respiratio in 

 cacumine JEtng absolvitur, ac in locis subjectis 

 campestribus. c Respiration is performed with 

 the same ease on the top of Etna, as in the coun- 

 try below.' 



" Several writers have treated of the difficulty 

 of respiration experienced by those who travel v 



over high mountains, and other inconveniences 

 to which they are exposed; but none, in my 

 opinion, more judiciously than M. Saussure, in 



