134 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
Mount Hamilton is about 128 km. from the origin, and if we assume that for distances 
of a few hundred kilometers the duration of the first preliminary tremors is proportional 
to the distance which the approximate straightness of the hodographs of the first two 
phases near the origin indicates, we find the following relation between the distance d 
and the duration ?’ of the first preliminary tremor: . 
d (km.) = 14.27 (sec.). 
As the position of the origin is not known nearer than 20 km. the number in the second 
member may lie anywhere between 12 and 16.2. 
