OBSERVATORIES AND THE DATA OBTAINED. 
In the following list the observatories are arranged in the order of their distances from 
the origin of the disturbance, and the map, plate 1, shows their positions graphically; it 
also shows their distances from the origin and the courses followed by the earthquake 
waves.’ The distances of the stations are calculated along the are in degrees and in 
kilometers, and along the chord in kilometers. In calculating these quantities the ordi- 
nary trigonometrical formule are used. The earth is considered spherical with a radius 
of 6,370 km.; which gives 111.18 km. for the length of one degree of are. (We can readily 
convert kilometers into miles by multiplying by 1.61.) In the collection of data all 
information available aiding in the interpretation of the seismograms is given. Altho 
other instruments in the same observatory may have recorded the shock, only those 
whose records were obtained are mentioned; and all their constants, so far as possible, 
are given. The component indicated refers to the direction of the earth vibrations 
recorded; for instance, a horizontal pendulum in the meridian would record the east- 
west component. The abbreviations used have the following meanings: 
T., the complete period of the pendulum without damping. 
V, the magnifying power for very rapid vibration. 
J, the indicator length, as used by Professor Wiechert. It is the product of the 
length of the simple mathematical pendulum, having the same period, mul- 
tiplied by the magnifying power, V. Its value is therefore (T' /2 7)’ g V. 
It is also given by a/w, where a is the displacement of the pointer due to 
a tilt, w, of the ground. On account of friction these two values do not 
always agree. The value obtained by the first method is given; and 
Angular displacement gives the displacement of the pointer due to a tilt. 
L, the distance of the center of oscillation from the axis of rotation; it equals 
the length of a mathematical pendulum of the same type, as defined on 
page 155. . 
L’, the length of the simple mathematical pendulum having the same period. 
Its value in meters is practically the square of half the period in seconds. 
M, the mass of the pendulum. 
e, the damping ratio of the vibrations. 
r, the frictional displacement of the medial line, as defined on page 163, and 
shown in fig. 43. 
In the majority of cases the values of the constants, or data sufficient to calculate them, 
have been supplied by the director in charge of the instrument; in the case of the Milne 
or the 10-kilogram Bosch-Omori instrument, the values of some of the constants could 
be obtained from exactly similar instruments installed in Baltimore. The value of L for 
the Wiechert inverted pendulum is taken from Dr. Etzold’s report on the Leipzig instru- 
ment. The times of the arrival of the different components at the station as recorded 
by the various instruments refer to the first preliminary tremors, the second preliminary 
tremors, the regular waves, the principal part, and the maximum disturbance. The hour is 
usually omitted as unnecessary; when the times are reported in minutes and seconds, 
they are indicated thus, 21" 43°; when they are reported in minutes and tenths of min- 
utes they are indicated thus, 21.7. The interval of time required for the waves to reach 
the station is given by subtracting the time of the shock, 12™ 28° or 12.5™, from the time 
of arrival. The amplitude is the displacement of the pointer. from its position of equilib- 
rium measured on the seismogram in millimeters, and always refers to the maximum dis- 
turbance unless it stands opposite some other time. The earth’s amplitude is the corre- 


1 Errata. — Two of the stations have been slightly misplaced. Kodaikanal, Madras, should be about 
2.5 mm. north of the southern end of India and about equally distant from the sea to the east and west. 
Mauritius should lie in the southeastern angle between the line marking 20° S. latitude and the red 
north-south line thru the antipodes of the origin, and practically touching these lines. 
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