MESSRS. J. MILNE AND T. GRAY ON SEISMIC EXPERIMENTS. 
875 
Records obtained with horizontal-lever seismograph. Ball fell 35 feet, unless 
differently specified. 
Number 
Station. 
Maximum 
amplitudes. 
Number of 
visible vibrations. 
of fall. 
Normal 
vibrations. 
Transverse 
vibrations. 
Normal. 
Transverse. 
Remarks . 
17 
feet. 
100 
millims. 
3 
millims. 
2 
millims. 
6 
millims. 
13 
Normal vibrations drawn in 1 second, 
18 
100 
3 
1-5 
7 
12 
transverse in 2 seconds. 
Transverse drawn in about 3 seconds (?). 
21 
200 
1 
1 
4 
12 
In both the above records of the trans¬ 
verse vibrations small irregular ripples 
apparently due to the direct wave or to a 
looseness in the joints of the instruments 
are shown. 
22 
200 
1 
1-5 
6 
12 
23 
200 
1 
1 
6 
10 
26 
100 
2 
1-25 
16 
18 
Produced in 4 seconds. 
27 
100 
2 
1-25 
15 
18 
„ 3^ seconds. Ball fell 25 feet. 
33 3^- ,, 33 18 ,3 
33 % 2 3 3 33 8 „ 
28 
100 
1 
1-5 
8 
9 
30 
100 
0-75 
1 
11 
16 
Records obtained from the rolling sphere seismograph. Ball fell 35 feet. 
Number 
of fall. 
1 
Maximum amplitudes. 
Station. 
Normal 
vibrations. 
Transverse 
vibrations. 
Remarks. 
feet. 
millims. 
millims. 
19 
100 
4 
1-25 
18 distinct waves in 3 seconds. 
24 
250 
1 
(?) 
25* waves. Direction of motion of plate was parallel to the 
direction of the transverse waves, which therefore cannot be 
measured. 
25 
250 
2 
(?) 
34* waves in 10 seconds. The transverse motions are too 
much compounded with the direct vibrations to be measured. 
Sixth Set of Experiments. 
On the line A D. 
The only difference between these experiments and the preceding ones is that the 
smoked glass plate was drawn along parallel to one of the pointers in order to avoid 
the possibility of any rotational movement taking place. This precaution, although 
apparently necessary when making experiments for the determination of velocity, does 
not, in the result, show that the former method gave any errors. 
* It is probable tliat either from bad adjustment of the instrument or from an independent motion of 
the ground the instrument has exaggerated the duration of the motion in these two cases. 
