ON THE VOLCANIC PHENOMENA OF VESUVIDS. 



286 



edge to the S., and another flowed across the crater plain in a westerly 

 direction; but in two or three hoars all outflow and movement of the 

 lava had stopped. I have shown elsewhere that the quantity of outflow 

 is proportioned to the depth of column tapped, but is more than the 

 quantity contained in the chimney above the tapping. This was exactly 

 what occurred in these two cases of January 1 and 6. This outflow 

 slightly lowered the activity for a few days, but observations were much 

 impeded by cloud cap. 



On January 19 lava again burst forth to the N.E. and moved for- 

 ward and outwards, a slice of about a fifth of the cone of eruption, just as 



Fig. 2. — Diagram of the Summit of the Great Vesuvian Cone, September 31, 1888. 



.'•'"O^aier of ~187^''--,^ 



..f/^ 



(y^^:^^^-^^^^>. 



The letters correspond to those of Fij;. 1, except the following : i indicates the cone of 

 eruption of autumn of 1888 ; i', the mouth of the volcano. 



a partly withdrawn slice of a circular cake. Professor J. D. Dana has 

 lately shown a somewhat similar displacement, though on a very grand 

 scale, in the Hawa'ian Islands. The lava issued at a lower level than in 

 the preceding eruption, and therefore flowed more abundantly. It seems 

 to have built up a platform in the eastern half of the crescentic fossa, 

 overflowed its edge and that of the great cone in a N.E. direction. In 

 fact, it is not improbable that it issued by a cleft in the E.N.E. edge of 

 the great Vesuvian cone. Central eruptive activity again diminished for 

 a few days, but returned again about the 27th of the month, so that the 

 ejections rapidly repaired the irregularity in the cone. This restoration 

 of cone-building persisted up to the middle of February, but observa- 



