OBSERVATORIES AND THE DATA OBTAINED. 69 

First PRELIMINARY | SECOND PRELIMINARY 

TREMORS. TREMORS. Max. AMPLITUDE. 
min. min, min. mm. 
26.2 to 28.2 17 + 
East component . . 19.5 24.4 | 28.9 to 32.1 174 
Interval .. . 7.0 11.9 

The instrument was not perfectly still and the time of the beginning is difficult to 
determine. The time given is that of the observer in charge. There is a well-marked 
movement 0.6 minute later, which may mark the arrival of waves reflected once inter- 
nally at the earth’s surface. The time of arrival of the long waves is not definite. There 
are large vibrations at 26.6™ and others at 29.1"; the latter fit the hodograph of the 
regular waves, but they are too uncertain and have not been used. 
OTTAWA, CANADA. 
Astronomical Observatory. Dr. Otto J. Klotz, director. 
Lat. 45° 24’ N.; long. 75° 43’ W.; altitude, 82 meters; distance, 35.37° or 3,932 km. ; 
chord, 3,871 km.; direction, N. 62° E. 
Foundation, boulder clay. 
Seismograms, sheet No. 10. 
The instruments used were Bosch-Omori horizontal pendulums, two horizontal com- 
ponents; photographic registration. 
(1) North component: 7, 5.71 seconds; V, 120; J, 970 meters; ¢, 1.50; 7, 0.0 mm.; 
M, 200 gm.; L, 6.68 cm. 
(2) East component: 7,, 7.06 seconds; V, 120; J, 1,500 meters; e€, 1.76; r, 0.0 mm.; 
M, 200 gm.; L, 6.68 cm. 
First PreLiMInAarRY SEcOND PRELIMINARY PRINCIPAL 
TREMORS. TREMORS. Part, 
m 8. 



™. 8. m,. &. 
(1) North component . 19 25 24 50 30 40 
(2) East component 19 12 oe ee 31 20(?) 
Average . 19 19 24 50 31.0 
Interval . 6 51 12 22 18.5 


The east component began 13 seconds before the north; this indicates that the longi- 
tudinal motion began before the transverse. The north earth-amplitude (one minute 
after the beginning) was 0.004 mm.; and the east earth-amplitude (0.5 minute after 
beginning) was 0.005 mm. These values are somewhat uncertain on account of the 
closeness of periods. The periods of the waves are not very different from that of the 
pendulums. On the north component the motion became so large for 10 minutes after 
31.0™ that it can not be followed; it then dies down to quiet at about 165 30™. On the 
east component the records are superposed so that the phases can not be distinguished 
after the beginning. 
WASHINGTON, DISTRICT OF COLUMBIA. 
U.S. Weather Bureau. Prof. Willis L. Moore, chief; Prof. C. F. Marvin in charge of 
seismographs. 
Lat. 38° 54’ N.; long. 77° 03’ W.; altitude, 20.5 meters; distance, 35.44° or 3,939 
km.; chord, 3,878 km.; direction, N. 74° E. 
Foundation, firm clay and gravel; solid rock probably within 8 meters. 
Seismograms, sheet No. 8. 
