ON SEISMOLOGICAL INVESTIGATIONS. 59 
Pendulum B also records east-west motion; it stands near to A 
on another brick column. ‘The cross-section of this is 18 inches by’ 
37 inches. 
Pendulum C records north-south motion ; it is installed on the same 
column as B. The stiffness of these two piers, as might be inferred 
from their dimensions, are very different. In an east and west direction 
the B-C column is approximately four times as stiff as A column (see 
‘B.A. Report,’ 1902, p. 60). 
For certain intervals of time, each of several months’ duration, these 
pendulums have been adjusted to have the same or different periods. 
When A and B had the same period, had they been loaded equally and 
installed on the same support we should expect that they would have 
attained a maximum swing at the same time. The following analyses 
show how far this was the case, notwithstanding the absence of this 
equality of conditions. With the object of comparing similar phases of 
motion, in all instances where time measures are concerned, reference 
has been made to the original seismograms. The earthquakes considered 
are indicated in the Shide Registers by the following numbers :— 
666, 671, 672, 674, 676, 679, 686, 690, 694, 704, 705, 794, 806, 
876, 832, 839, 859, 860, 861, 863, 872, 877, 884, 886, 900, 903, 904, 
924, 952, 975, 977, 982, 990, 994, 1001, 1020, 1021, 1031, 1038, 1045, 
1046, 1048, 1057, 1064, 1065, 1070, 1074, 1087, 1111, 1118, 1135, 
1145, 1164, 1182, 1190, 1208, 1225, 1242, 1257, 1266, 1281, 1284, 
1293, 1303, 1319, 1820, 1322, 1323, 1362, 1363, 1375, 1387, 1390, 
_ 1398, 1408, 1412, 1419, 1422, 1425, 1428, 1431, 1433, 1439, 1450, 
1460, 1463, 1468, 1471, 1475, 1495, 1496, 1515, 1522, 1526, 1532, 
1540, 1544, 1549, 1563, 1564, 1568, 1575, 1577, 1585, 1591. 
No. 1.—For thirty-seven earthquakes A and B have had the same 
periods. For twenty-five of these a maximum motion was recorded 
at the same time; for the remaining twelve earthquakes the difference 
in time for the maximum swing was two minutes or over. 
No. 2.—For twenty earthquakes A or B had the same period as C. 
For eleven of these maximum for north and south motion occurred at the 
same time as the maximum for east and west motion; for the remaining 
nine earthquakes there was a difference in time for the maximum motion 
of two or more minutes. 
No. 3.—Out of 103 earthquakes A and B have had the same period 
for thirty-seven earthquakes; for the remainder they had different 
periods. Taking these en bloc, A and B have recorded maximum swing 
at the same time in fifty-one cases; in the remaining fifty-two cases the 
times for this movement have differed by two or more minutes. 
No. 4.—Pendulum C (north-south motion) indicates a maximum 
— very frequently before a maximum motion is recorded by A 
and B. 
I do not see that the district from which an earthquake originates 
has any relationship to the pendulum which first records its apparent 
maximum motion. 
VIII. The Number of Earthquake Records obtained at British 
Stations. 
In the ‘ British Association Report,’ 1901, pp. 44-50; 1902, p. 73; 
and 1903, p. 82, references are made to the number of records obtained at 
