Page:Popular Science Monthly Volume 69.djvu/129

Rh a point on the opposite side of the earth from the origin in about 20 minutes; the latter are supposed to pass directly through the earth. In computing the velocities I have taken provisionally as the average

 at the Magnetic Observatory, Cheltenham, Maryland, reduced 2 times. [The hours as marked are approximately local mean time. The earthquake effect will be noticed on the three magnetic elements, horizontal intensity, declination and vertical intensity in the shape of a trumpet formation between 8 and 9 a. m., local mean time. The range or double amplitude of the disturbance was about 1,1000 part of the horizontal intensity and about 1/3000 part of the vertical intensity. On account of the intersecting of the curves, the range in the magnetic declination cannot be given.]

time of the shocks on the Pacific Coast which gave rise to the effects recorded at distant places as occurring at 5$h$12$m$ Pacific time or 13h 12m, April 18, Greenwich time. There may have been earlier preliminary shocks.