126 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
TaBLeE 14.— Time Intervals and Weights of Observations for determining the Hodograph of 
the Regular Waves. 
TiME 
INTERVAL. 
STATION. DISTANCE. STATION. DISTANCE. 1seoeene WEIGHT. 


min. 
SOIT Ka aon 10.07 Tortosa 
. Tacubaya . . 13315 Krakau 
. shorn tOe Ee 15.40 : . } Granada . 
Washington 17.33 Pavia . 
Cheltenham : Vienna. 
. Trinidad . . 29.50 Lae 
{ Paisley . K agreb. 
- | Edinburgh eee. sl sie 
Tokyo 7 uarto-Cas- 
Bidston . 34.78 tello. . 
Upsala . Zi-ka-wei . 


Shide... 5 . Rocca di Papa . 
Osaka. . ; 37.30 . Ischia : 
Kobe. . . Caggiano 
Ke Wane Pisveyiny = 
Hamburg 39.03 . Catania . 

Irkutsk . . Wellington . 
Potsdam . . Calamate , 
Gottingen 38.65 f Christchurch . 
Coimbra . * | Manila . 
Leipzig . . Calcutta . 
Jena . . 36-00 . Bombay . 
aMuniche. eine. 39.25 . Batavia . 
. Perth Man eee 
. Cape of Good Hope 





Rowe ND HE woe wee 



The observations used come from 47 stations, but they are only represented on the. 
plate by 27 points, on account of the grouping together of stations at very nearly the 
same distance from the origin. The hodograph is determined from nearly twice as many 
stations as would be inferred from a cursory glance at the plate. Wecan not assume that 
the straight hodograph, determined from these observations, passes thru the origin; but 
we seek the position of a straight line in general which will best fit the observations. 
The general equation of a straight line is y = ma + b. In this case y is the time of 
arrival of the long waves, x the distance of the station from the origin in degrees, m the 
reciprocal of the velocity of transmission, and b the point where the line cuts the axis of 
y; —b/mis the point where it cuts the axis of x. On working out, by the method of 
least squares, the most probable values for m and 6 according to the weighted observa- 
tions, we find 
m = 0.494 min./deg. b = — 0.91 min. 1/m = 2.03 deg./min. 
The velocity of the regular waves 1/m is equal to 2.03 deg./min., or 3.75 km./sec. ; 
and the point where the line crosses the axis of x is given by — b/m, which equals 1.84° 
or 205 km. These are the most probable values of the quantities concerned as deduced 
from the observations, but they are the result of a very limited number of observations 
and might be modified by results obtained in other earthquakes; and therefore we can 
not suppose that the constants are very accurately determined. On the other hand, 
the observations are in fair agreement with each other and therefore the results can not 
be very far wrong. 
The fact that the straight line does not pass thru the origin, but crosses the axis of x 
at a distance of 205 km. from the origin does not mean that the regular waves start at this 
point at the time of the shock. Indeed, we have no observations at all along this part of 
the line, but there is a very simple explanation of the fact that the line does not pass 
thru the origin. This is that the regular waves are generated by one of the first two 
phases at the surface of the earth at a short distance from the origin. The point and 
