64 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
LOS GATOS, CALIFORNIA. 
Private observatory. Irving H. Snyder. 
Lat. 37° 14’ N.; long. 121° 59’ W.; distance, 1.04° or 115 km.; direction, 8. 38° E. 
Foundation, on soil not far from solid rock. 
Seismograms, sheet No. 3. 
The instruments used were Rocker seismographs. Two lead bars are each supported 
at the center of two thin circular segments, so that they rock easily on a smooth plate, one 
in a north-south, and one in an east-west direction. The movements of these rockers are 
recombined by means of levers and a record is made on smoked glass entirely analogous to 
the records of a Ewing duplex pendulum. The movement of the earth was magnified 
about four times. 
The arrows show the directions of the motions. If the marking point is supposed 
stationary, it would be necessary to interchange the directions north and south, east and 
west, in order to represent the true movement of the earth. The movement seems to have 
begun in the blurred mark near the middle of the seismogram and the first distinct move- 
ment of the pointer was towards the west, and therefore the first distinct movement of 
the earth was towards the east. This was followed by movements in various directions; 
the violence of the disturbance quickly disarranged the rockers, and the record is very in- 
complete. The recorded earth-amplitude is only 5 mm.; but this was much less than the 
real maximum. 
MOUNT HAMILTON, CALIFORNIA. 
Lick Observatory. Prof. W. W. Campbell, director. 
Lat. 37° 20’ N.; long. 121° 39’ W.; altitude, 4,210 meters; distance, 1.16° or 129 km. ; 
direction, 8. 53° E. 
Foundation, solid rock; the observatory is on the summit of Mount Hamilton. 
Seismograms, sheet No. 3. 
The instruments used were: (1) Ewing three-component seismograph; V: north-south 
component, 4.2; east-west component, 4; vertical component, 1.8. The reproduced 
selsmogram is only half the size of the original and therefore it only magnifies the dis- 
placements half as much as indicated above. 
(2) Ewing duplex pendulum, V, 4. In reading the actual movement of the ground 
from the duplex record we must interchange the directions east and west. Both 
instruments record on smoked glass. The duplex record shows that the earth first 
moved for a distance of 7 mm. in a direction S. 60° E., that is, away from the origin; this 
was followed with some irregularity, by several vibrations parallel with this direction, 
with increasing amplitude, and then the movement became confused; there was much 
jumping of the pen, and as much of the movement was not recorded, the pen must have 
been held off the plate. Unfortunately we can not say positively when the movement 
recorded on this instrument began, but its amplitude makes it most probable that it 
began at the same time as the record on the other instrument, namely at 5° 12™ 45°. 
Altho the earthquake was first felt at Mount Hamilton at 5° 12™ 12°, the Ewing 
three-component seismograph was not set in motion until 5° 12™ 458; that is, it was 
started by the violent shock. This was the nearest instrument to the centrum that was 
driven by a clock and which separated the various phases of the shock. We note that 
for 9 seconds the disturbance was comparatively slight and then came the strong move- 
ment which carried the pens beyond the limits of the glass plate. The north-south com- 
ponent was soon caught and, with the exception of one spasmodic swing across the plate, 
did not record again for 1 minute 40 seconds, by which time the disturbance had very much 
diminished. The east-west component seems to have been better placed, for altho 
