TRANSACTIONS OF SECTION C. 501 
instruments, as these are placed similarly to the towns on mountains, where the 
earth-wave passes beneath them, as illustrated by Mallet. 
Dr. Samuel Haughton has calculated from projected objects the molecular 
velocity, which turns out to be 4°64 feet per second. The maximum molecular 
velocity was determined in three cases, and found to be 4087, 4°553, and 5:273 
feet per second respectively ; the mean of all being 4:64 feet per second, 
The velocity of transmission could not be obtained, partly on account of the 
small distances within which clocks were stopped, and the imperfect time kept. 
The number of deaths resulting from this earthquake were 127. 
It is said there were changes in the temperature of the mineral waters and 
fumaroli, but the author was unable to verify if such had really been the case, and 
when he examined thermometrically the principal ones, some days after, he could 
not find any important variations from their usual state. 
4, Preliminary Notice on the Earthquake of July 1883 in the Island of Ischia. 
By H. J. Jounsron-Lavis, F.G.S. 
On July 28, 1883, at 9.25 p.m., a violent shock of earthquake reduced to 
ruins Casamicciola, including the districts of Tresta, Olivieri, Panella, Casamonte, 
Mezzavia, most of Lacco, Fango, Monterone and Vajola di Forio; injuring very 
severely the rest of Lacco, Monticchio, the greater part of Forio, Panza, Serrara- 
Fontana, Fontana, Maropano, Barano, Piejo, Faiano, and Rotaro. 
Beyond this extends a third area, covering most of the island, in which the houses 
were only slightly fissured. 
The isoseismals have almost exactly the same form and arrangements as in the 
earthquake of 1881, but from the far greater violence of the shock, they are 
naturally larger. The houses included within the mesoseismal area—that is, Casa- 
menella and the Purgatorio district of Casamicciola, with part of Fango—were ruined 
to such an extent that hardly the stumps of the walls were left, and it was rare to 
find a piece of masonry which was not reduced into its ultimate fragments, so that 
it was uncommon to find two or three stones still attached together. Objects were 
projected considerable distances, the iron tie-bars put into walls after the 1881 
injuries were broken and bent like thin iron wire. 
One fact very remarkable in this last earthquake was the effect of geological 
structure. Thus, for instance, all the houses situated on the brink of a valley where 
the tufa was loose and incoherent, were in most cases quite destroyed from the fis- 
sures of an incipient or complete landslip. Buildings with foundations on the loose 
alluvial tufas of the plains of valley bottoms have suffered much less than others 
built directly upon the solid tufa. "We may compare, for instance, Casamonte and 
some farm-houses on the little plain close at hand. The most remarkable effects of 
this kind are the Marinas of Casamicciola and Lacco-Ameno, where some houses, 
that are built entirely on loose sea-sand, have only nominally suffered, whereas 
houses built on the tufa, and only a few paces distant, are more or less ruined. 
Faiano, which is almost in contact with the large masses of trachyte of Monte 
Toppo and Monte Vetta, has suffered very severely, probably as the result of the 
different vibratory increments of two materials differing so widely in their elas- 
ticity. It is no doubt due to the rapid annulling by absorption, refraction, and re- 
flection from the media traversed, that all volcanic earthquakes are so very limited 
in their extension. 
Besides the actual damage done to the houses, a number of landslips occurred, 
three of which are worthy of remark for their extension. A large one detached 
itself from the side of Monte Rotaro, overhanging a part of the Vallone Ombrasco. 
Two others started near the summit of Monte Nuovo (of Ischia) and swept down 
its north-eastern and north-western flanks, destroying a large tract of vine-gardens. 
In the former case the landslip occurred through the loose fragmentary ejectamenta 
of Monte Rotaro, whereas in the other two cases the materials were the much 
altered Epomeo tufas, that have been for centuries exposed to the destructive 
fumarolic action. This latter gave rise to some extraordinary exaggerations, such 
