OBSERVATORIES AND THE DATA OBTAINED. 79 
(2) East component: 7, 28.22 seconds; V, 64.9; J, 13,000 meters; e, 1.005; 1, 0.0 
mm.; M, 50 gm.; L, 13.3 cm. 
First PRELIMINARY | SECOND PRELIMINARY 
TREMORS. TREMORS. 

8. ™m. 8. 
(1) North component. . 45 34 43 
(2) East component . . . 41 34 49 
Average Pret ae te 24 43 
Interval aint oso 1G cc 15 


_ The seismograms are carefully drawn from the original, parts of which were so faint, 
on account of the rapid movement, that they could not be reproduced. (The correction 
to G. M. T. should be +43 seconds and not —48 seconds, as marked on the seismo- 
grams.) ‘The north component begins in the middle of the sheet at the bottom of the 
seismogram; it had an amplitude of 15 mm. when the sheet was put on. This move- 
ment gradually died down, but the pendulum was not perfectly still when the earthquake 
arrived 3" 10™ later. The first preliminary tremors have a small amplitude, about 1 mm., 
and a period the same as the period of the pendulum, showing an extremely small dis- 
turbance. The second preliminary tremors have an increasing amplitude from about 
10 mm. to 20 mm.; at 13" 50™ 45° the motion becomes so large and the photographic 
record so faint that it can not be copied; a few turning points are shown in the lower 
part of the plate; this continues for the rest of this line. The record is again picked up 
at the beginning of the next line at about 14”. The center of the record is shown by the 
single line on the left of the plate. The movement gradually dies down, but still has an 
amplitude of 20 mm. two hours later. The east component begins in the middle of the 
sheet; it has small oscillations which entirely die out before the preliminary tremors 
arrive. The first preliminary tremors and second preliminary tremors begin at the 
same time as those of the north component, but they have larger amplitudes, the first 
attaining an amplitude of 7 mm.; and the second, beginning with nearly 50 mm., attain 
120 mm. by 13" 48", and a few minutes later (13" 53” 45°) are lost. They are picked up 
again 8 minutes later, and about 14” 25™ drop to an amplitude of about 40 mm.; they 
then gradually die out more irregularly than the other component. The very large am- 
plitudes are due to synchronism of the periods of the waves and the pendulums. 
IRKUTSK, SIBERIA. 
Meteorological and Magnetic Observatory. M. A. Voznesenskij, director. 
Lat. 52° 16’ N.; long. 57° 14’ E.; altitude, 470 meters; distance, 80.82° or 8,986 km. ; 
chord, 8,259 km.; direction, N. 27° W. 
- Foundation, hard Jurassic clay. 
The instruments used were : 
Repsold-Zdllner horizontal pendulums, two components; photographic registration. 
Seismograms, sheet No. 2 a. 
(1) North component: 7'o, 35 seconds; V, 57.5; J, 17,500 meters; angular displace- 
ment, 1 mm. = 0.011”; M, 30 gm.; ZL, 14 cm. 
(2) East component: 7, 25.5 seconds; V, 57.5; J, 9,300 meters; angular displace- 
ment, 1 mm. = 0.021”; M, 30 gm.; ZL, 14 cm. 
Bosch-Omori horizontal pendulums, two components; mechanical registration on 
smoked paper. Seismograms, sheet No. 13. 
(3) North and (4) East components: 7’, 24 seconds; V, 10 (?); J, 1,480 meters (?); 
Mealike(?)-.L, 75 cm. (2). 
