104 Prof. Cavalleri on a New Seismometer. 
quake, as exhibited in the effects which it has produced, is a far 
superior method. But besides the difficulty of giving, among a 
mass of effects apparently contradictory, the due value to each, 
we should remember that frequently the earthquake leaves no 
distinct trace of direction, origin, or intensity, and still more 
frequently no trace whatever. And yet these weak and disre- 
garded perturbations might afford precious data to science. ‘The 
study of seismometers appears to me very useful, if it be possible 
to add anything to what we have already done. A perfect 
seismometer should record the traces of the various motions 
which affect the surface of the earth, at once marking their com- 
mencement, duration, and relative intensity. The formation of 
one seismometer which should embrace these complex phzno- 
mena being almost impossible, I perceived at the beginning of 
my work that it was necessary to divide them into their com- 
ponent parts. Such a division being made, the invention of an 
instrument which should record these components, or we might 
say elements of the complex motion, became much easier. Iam 
not unacquainted with the many scismometers made and pro- 
posed by others, and have endeavoured to profit by their designs ; 
but, none appearing to me satisfactory, I have changed and added 
to their plans. I subjoina description of the apparatus which I 
have constructed and recently tried. 
A brass ball, weighing 3 kilogrammes, is vertically suspended 
by a wire 1 millim. in diameter ; this wire, in length 1°25 metre, 
is fastened at the point of suspension to the end of a strong 
iron plate by means of a screw; the plate is secured in the wall, 
and projects horizontally from it 5°38 decimetres. A needle is 
firmly attached to the lower part of the ball with the point turned 
down and finely sharpened; in length it is 9 centimetres. The 
apparatus isin fact a pendulum. The extreme point of the needle 
is inserted a millimetre or a little more into an extremely small 
cylinder or square prism (viera), but so as to be quite free. This 
cylinder rests lightly on the summit of a small support or vertical 
column fixed in the centre of an iron pan which is firmly attached 
to the wall. The pan is filled with finely-sifted ashes or brickdust 
to the level of the needle’s point, or a little higher, as may be seen 
in the accompanying Plate (PI. I.). The apparatus being arranged 
in this manner, it is evident that if a shock occurs, let us sup- 
pose from the south, the ball of the pendulum, owing to its own 
mertia and the time necessary to transmit the motion from the 
top of the wire to the ballitself, will remain unmoved; while the 
wall, the fixed plate which holds the pendulum, the pan, and 
the support of the small cylinder will be pushed at the same 
instant towards the north. By the simultaneous motion of all 
the rigid parts of the apparatus, the support of the vertical 
