7m 
PROCEEDINGS OF SECTION H. 
the size of the walls, and, fortunately for seismic inquiry, there is no 
want of such in the south of Italy” ; and, again, “ Fissures in walls 
not overthrown are the sheet anchor, as respects direction of the 
wave path, to the seismologist in the field.” Taking these for data, he 
made the calculation for the first approximation to the depth of the 
focus ever attempted for any earthquake. lie was at the same time 
able to measure for the first time the velocity of transit, and the 
velocity of the wave particle at its maximum. He might well be 
pardoned for displaying some elation on announcing these facts, 
w Geologists,” he says, “ must not be surprised to find that they differ 
enormously from each other, that the velocity of transit is about half 
that of a cannon shot ; but the velocity of the wave particles which 
does the mischief is not as great as that with which a man reaches the 
ground when he jumps off a table, and yet that this small velocity is 
competent to produce all the violent and formidable effects of earth- 
quakes no longer admits a doubt.” 
As to his second order of inquiry — and to architects the most 
interesting — he has by implication shown us what material to avoid and 
what is suitable ; he has also shown how, with good workmanship, our 
buildings may be rendered capable of withstanding an earthquake of as 
great severity as that of which he writes. For instance, he says: ‘‘There 
is no cause for wonder at the great destruction, the wonder is there 
was not more,” and thus describes Italian architecture: “The usually 
grandiose effect of their buildings generally conceals workmanship of 
a very inferior quality. The floors of the better sort of town houses 
are formed of joists of fir, commonly round as they grew, and from 
§ to 9 inches in diameter, placed about 3 feet apart, the ends 
inserted a few inches into the wall, but neither bedded on nor 
connected by any tossils or bond timbers, none of which are ever 
placed in the walls. On these joists a planking of fir, oak, or chest- 
nut, an inch or an inch and a-half thick, rough from the saw is laid, 
and upon it a bed of concrete or beton composed of lime, mortar, 
broken tufa, brick, or stone, is next laid, with red tiles on top, or 
sometimes plastered over with mortar, and painted in oil. A floor of 
this sort weighs from 60 to 100 lb. per superficial foot, the roofs being 
more primitive and weighty.” 
The chief difference in point of masonry from those in country 
towns is that surface limestone or exposed beds of rocks are commonly 
used. Hence the walls built almost invariably of this coarse, “nobbly” 
rubble, in half-round blocks, or of lumps of stone, in form like irregular 
loaves of bread, are almost devoid of bond, and are shaken down into a 
heap by forces that would only fissure a well-built and properly bonded 
structure. It is upon these heavy floors and roofs, with the defective 
masonry described, that the most instant and formidable effects are 
produced by vertical emergence. Upon these the velocity produces a 
moment of inertia, acting directly downwards, and therefore favoured 
by gravity, arched roofs, joining, and that form of arched ceiling con- 
structed of hollow pottery. I am not aware of the ultimate flexibility 
or elasticity of stone in brickwork, but Mallet is of opinion that both 
arc small, even in w r ork of the highest quality, but prefers brickwork, 
as it possesses an extent of flexibility in a far higher degree than the 
masonry, the bond of the mortar being better, the flexibility greater, 
both in the bricks and numerous mortar joints, and the elasticity 
