ON SEISMOLOGICAL INVESTIGATION, 223 
glass cup carried by a support fixed to the wall. The position of the cup 
can be adjusted by screws, both horizontally and vertically. The base of 
the bob is slightly conical, and in its centre a hole is made, covered by a 
sheet of brass, in which a small hole with bevelled edges is made which 
clasps the needle, FG, at the point H. By means of the adjusting screws 
fitted to the glass cup, the points G and E of the needles are placed as 
nearly as possible in a vertical line below the centre of gravity of the bob. 
So long as the bob remains steady the point H is the fulcrum of the lever, 
and the movements of the wall are magnified at the end E in the ratio 
Fig. 14, 
EH to GH. The total weight of this lever is 2-2 grammes ; its length is 
144 mm., and the ratio EH to GH is equal to 16. The friction at both 
the points G and H is extremely small. 
The movements of the lower end of the vertical lever are magnified by 
two light horizontal levers (fig. 14), which give the components of its 
motion in directions at right angles to one another. It should be mentioned 
that this figure is not drawn exactly to scale, and illustrates the slightly 
law arrangement in a new microseismograph recently erected at 
‘adua. 
One of the levers, K, is rectilinear, and the other, K’, bent at right 
angles, In the Siena instrument they are made of thin aluminium plate, 
terminating, at the ends L and L’, in two very thin burnished steel 
needles, parallel to one another, and separated by a distance equal to the 
