•±30 F. A. Perret — Vesuvius. 



be seen ascending near the still falling avalanche and thus 

 forming two columns moving in opposite directions. 



The avalanches have recently become more numerous. This 

 is due, in my opinion, to increasing tension within the volcano, 

 which causes the detachment of the materials by producing 

 slight earth tremors. The northerly half of the crater rim is 

 being by their means considerably reduced in height and 

 altered in contour, as has already been shown in the section on 

 morphology. 



On this side of the cone I have recently observed, on a very 

 small scale, a replica of the great external avalanches which 

 formed so conspicuous a feature of the last eruption. The 

 present ones are formed, curiously enough, in connection with 

 those on the inside of the crater. So sharp is the rim on this 

 side that when it crumbles a portion of the material, with 

 possibly a bowlder or two, falls outward instead of inward and 

 forms the nucleus of the external slide, which is limited by the 

 small amount of readily movable substances upon the cone at 

 present. 



The sand-spiracles which were numerous at the close of the 

 eruption, and which Lacroix and others have mentioned, are 

 still to be seen occasionally. Fine sand is caught up in a 

 vortex of wind forming a funnel like a miniature tornado, but 

 generally very narrow throughout its length and perfectly 

 straight. They have a rapid movement of rotation with a slow 

 one of translation. I have not yet had the opportunity to 

 photograph one of them. 



As to the future, it goes without saying that the remainder 

 of the repose-period, be it long or short, will be of even greater 

 interest than that which is already past. Fumarolic activity 

 should increase, earth tremors become stronger and more 

 frequent, until finally — if the volcanic action follows normal 

 lines — the magma shall have fused and forced its way upward 

 in the central conduit to the crater, when a new period of 

 external activity will be inaugurated. A systematic study of 

 the signs of its coming would be of great value to the science 

 of prediction. 



In concluding, the writer desires to acknowledge his in- 

 debtedness to Dr. Martin Henze for the chemical analyses, to 

 Prof. Mercalli for much valuble information and advice, to 

 Herr Faerber, of Thos. Cook & Son, for materially facilitating 

 his excursions on the mountain, and to Professor Jaggar for 

 revision of the proofs of this manuscript. 



Naples, Italy, Aug. 26, 1909. 





