222 REPORT—1896. 
venience of working in the dark, and of using an apparatus which does 
not give its record until the sensitive paper is developed, and to the great 
expense of the photographic paper, the chemical reagents, and the source 
of light. 
Fis first experiments were made with an ordinary tromometer, about 
1:50 metre long, and with a bob 50 kg. in weight. The support of the 
pendulum was fixed in a wall of the University buildings of Siena, over- 
looking a much frequented road, on the third floor, and about 20 metres 
above the ground. A short straw, terminating in a fine steel wire, was 
attached to the bottom of the bob, and the movements of the point of the 
wire were observed by means of a totally-reflecting prism and 
microscope provided with a micrometer. A tromometer of 
this kind does not give at any instant the true state of vibra- 
tion of the ground, its movements being affected by previous 
disturbances. But if the pendulum be obliged to perform a 
very little work, such as the movement of the light vertical 
lever described below (fig. 13), the bob is rendered much more 
insensible to the rapid vibrations of the point of suspension. 
Substituting this lever for the straw referred to above, the 
movements of the lower end were observed with the micro- 
scope. The superiority of this arrangement is very evident. 
When a carriage, for instance, approaches from a distance, 
the point of the lever at first vibrates parallel to the wall, 
‘then ina plane more and more inclined to it, until, when the 
carriage is just opposite the building, the vibrations are per- 
formed normally to the wall and are synchronous with the 
¢ trampling of the horses. When the vibration of the ground 
ceases, the movement of the lever ceases contemporaneously. 
Thus, by the application of this vertical lever, the bob of the 
pendulum is transformed almost into a steady mass, and its 
steadiness during movements of the ground is further pro- 
moted by the addition of the two horizontal levers which give 
the component movements in two directions at right angles 
2 to one another. ; 
In the complete microseismograph erected in the University 
of Siena, the bob of the pendulum weighs 50 kg., and is sup- 
@ ported by three chains, united at their upper ends in a brass 
cap, to which is attached an iron wire about 2 mm. in diameter. 
€ This is fastened to a screw in a strong iron bracket driven into 
the wall. The length of the pendulum is about 1:50 metre. 
By means of the screw the bob can be raised or lowered. Immediately 
below the latter are fixed two iron bars to support it, and prevent damage 
to the registering apparatus in case the suspending wire or chains should 
break. The bob is also surrounded by an iron ring carrying three screws, 
whose office is to prevent excessive displacements of the pendulum. When 
the pendulum is connected with the recording levers it performs complete 
oscillations in 2°4 seconds. 
Fig. 13 shows the vertical amplifying lever referred to above. It 
consists of a thin tube of aluminium A, soldered at its upper end to a ring 
B of the same metal. To its lower end is fixed a sewing-needle, DE, 
whose cylindrical part has a diameter of 0°6mm. The ring B is traversed 
at its highest point by a second needle, FG, exactly similar to the first. 
Its point, G, penetrating a short way inside the ring, rests in a small 
Fig. 13. 
