70 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
The instrument used was a Bosch-Omori horizontal pendulum; east component; 
mechanical registration on smoked paper. JT',, 32 seconds, V, 10; J, 2,540 meters; 
e, 1.35; r, 0.56 mm.; M, 17.35 kg.; £; 75.2 cm. Eerteaton 







F P ARY |SEconp P ary| R P ‘ 
mercer ep eer oo oe SELIG) ney nop kicires 
m. a: ee mM. 8. min, min. mm. 
East component. 19 20 25 00 29 20 30. 32 to 35 95 
Interval . . 6 52 12 32 16 352 18.0 

Duration, 4.3 hours. Perhaps the long waves should begin a minute earlier. The very 
strong motion only lasted about 4.5 minutes. During the second preliminary tremors 
the period was about 25 seconds, and amplitude 95 mm., corresponding to an earth- 
amplitude of 0.4mm. During the regular waves at 32.0" when the pointer went off the 
record, the period was about 30 seconds, practically that of the pendulum; so that we 
can not draw conclusions regarding the actual motion of the ground. 
CHELTENHAM, MARYLAND, 
Magnetic Observatory of U. 8. Coast and Geodetic Survey. O. H. Tittmann, super- 
intendent; W. F. Wallis, magnetic observer. 
Lat. 38° 44’ N.; long. 76° 50.5’ W.; altitude, 72 meters; distance, 35.64° or 3,962 
km.; chord, 3,899 km.; direction, N. 74° E. , 
Foundation, sands and gravel. 
Seismograms, sheet No. 8. 
The instruments used were Bosch-Omori horizontal pendulums, two horizontal com- 
ponents; mechanical registration on smoked paper. The corrections to G. M. T. are 
negative for both components. 
(1) North component: 7',,20 seconds; V,10; J, 1,000 meters; M, 10 kg.; L, 75 cm. 
(2) East component: 7, 25 seconds; V, 10; J, 1,560 meters; M, 10 kg.; LZ, 75 cm. 














Daa | no temuosa, ti Weiivas. |. apes Seen 
m. 8. m 8. m 8. min. sec, mm. 
(1) North component 19 30 25 01 30 00 | 32.3 t0 36 13 40 + 
(2) East component 19 16 25 09 30 32 | 32.8to39 9 35 + 
Average ... 19 23 25 05 380 16 | 32.5 
Interval . . . GU SS kes 12 are7 1748) 17:20.0 





Duration, north, 2.7 hours; east, 3.1 hours. The time of the first preliminary tremors 
on north component is not very definite, but it is not later than 19° 30™. The longitudi- 
nal waves apparently arrived some seconds earlier than the transverse. This probably 
means that the longitudinal waves were first felt, and then the disturbance became more 
complex.. The regular waves are a little earlier on the north than on the east 
component, as is also the strong motion. 
The dying-out curves sent me to determine the damping and friction are too irregular 
to yield definite results, which is probably due to irregular friction; but if we neglect the 
damping and frictional terms, we find the magnifying power of the north component for 
waves of period 13 seconds (135 34™) to be 17.3; and since the amplitude of the pendulum 
is 40 mm. that of the earth would be 2.8 mm.; with the same assumption, the magnify- 
ing power of the east component for waves of period 9 seconds (135 36™) is 11; and the 
corresponding earth-amplitudes, 3.2mm. But both of these values are too small, as the 
movements of the pendulums seem to have been limited by the stops. It is not unlikely 
that the total earth-amplitude at Cheltenham may have amounted to 5 mm. 
