60 



EARTHQUAKES. 



that the higher the initial impulse the greater was the 

 velocity. The velocity of propagation of the transverse 

 vibrations seemed to approach more and more to that of 

 the directed vibrations as the distance from the origin of 

 disturbance increased. Fig. 11 shows the nature of the 

 record obtained from the explosion of two pounds of 

 dynamite at the bottom of a bore-hole eight feet deep. 



Fig. 11. — Records obtained at three stations of the motion of the 

 ground produced by the explosion of 2 lbs. of dynamite. 



These records show the interval of time which elapsed be- 

 tween the arrival of the normal and the transverse vibra- 

 tions at points distant 100, 250, and 400 feet from the 

 bore-hole. In the case of the 100-feet station it will be 

 observed that the motion towards the origin is greater 

 than that from the origin. It is also to be noticed that 

 the period of vibration becomes greater as the distance 

 from the origin increases. 



