CHAPTEK IV. 



EARTHQUAKE MOTION AS DEDUCED FROM EXPEraMENT. 



Experiments with falling weights — Experiments with explosives — Re- 

 sults obtained from experiments — Relative motion of two adjacent 

 points — The effect of hills and excavations upon the propagation of 

 vibrations — The intensity of artificial disturbances — Velocity with 

 which earth vibrations are propagated — Experiments of Mallet — 

 Experiments of Abbot — Experiments in Japan — Mallet" s results — 

 Abbot's results— Results obtained in Japan. 



Experiments with Falling Weights, — A series of ex- 

 periments, as the nature of the disturbance produced in 

 the surface of the earth when a heavy weight is allowed 

 to fall on it, was begun in November 1880 by Mr. T. 

 Gray and the author. These experiments were carried 

 out at the Akabane Engineering Works in Tokio. The 

 weight used was a ball of iron weighing about a ton, 

 which in the different experiments was allowed to fall 

 from heights varying between ten and thirty-five feet. 

 The position of the place where the ball was allowed to 

 fall was such that in one direction the vibrations were 

 transmitted up the side of a steep hill, in another direction 

 across a pond with perpendicular sides, and in another 

 direction across a level plain the material of which con- 

 sisted for the most part of hardened mud extending to a 

 very considerable depth. The vibrations produced by 

 the fall of the ball were transmitted through this hard 

 mud with considerable intensity to a distance of between 

 300 and 400 feet. 



