Prof. Cavalleri on a New Seismometer. 107 
certain directions in preference to others, according to the differ- 
ent lie of valleys and mountains; and further, that these waves 
are broken in their course and reach a given point more or less 
late, thus occasioning confluxes of different waves all generated 
from the primary, so as to produce shocks more considerable than 
at spots nearer the first convulsion. This appears to be the ne- 
cessary consequence of the heterogeneous material of which the 
crust of our globe is composed. A single strong shock sent 
through strata of different density, arrangement, and elasticity, 
the strata also lying at angles widely varying from the direction 
of the primary impulse, and afterwards subject to different 
changes of dip (incidenza), must indubitably occasion—lst, a 
composition of forces; whence, 2nd, a different direction of waves; 
3rdly and lastly, varying velocity in their progress. These effects 
would of themselves be greatly complicated, even admitting that 
the waves should act only in one plane; but when we add, as 
truth requires, that the waves necessarily act in different planes 
according as the earthquakes are generated at a greater or less 
depth, and that the waves must radiate or expand, not over a 
single surface, but in a mass of three dimensions, every one must 
admit that the phenomena of earth-waves are most complicated, 
and have a thousand different aspects. Our instrument is capable 
of recording these anomalies and others which we are about to 
notice. 
When an earthquake occurs, the pendulum being disengaged 
from the cylinder, which falls in the direction from whence the 
first wave proceeded, is set at liberty, and traces in the ashes 
which lie beneath, and which rise a little above the point, the 
general direction of the wave. The application of the pendulum to 
tracing the direction of the earth-wave is already known, and has 
been frequently tried ; I cannot boast of adding anything further 
to this invention than a most important auxiliary. But here 
some observations present themselves which I consider very im- 
portant. The traces which the pendulum leaves impressed in 
the ashes, as I observed at Bologna during the earthquake which 
oceurred there last year, are in general more or less long and well 
marked. These are not occasioned by the oscillations of the 
pendulum itself, which are always relatively small, but by the 
ground moving under the pendulum. The pendulum is soon set 
in motion, but its oscillations are very limited, and take the form 
of ellipses,—at first very excentric, almost poimted; but they 
shortly lose their excentricity and increase their minor axes, until 
they become small circles. These figures are easily perceived 
if the point of the needle is sharp, and the ashes or brickdust 
smooth and regular, but only when the earth-wave proceeds from 
one direction. Should the waves come from two or more, it would 
