Vol, 6] Eeid: The Elastic-Rebound Theory of Earthquakes. 423 



At the time of the slip A and C remained stationary, and the 

 amount of the slip, DB, equalled the shift which A had originally 

 experienced. A straight line, A'C (fig. 4), was drawn on the 

 jelly after the left side had been shifted, but before the jelly 

 slipped along W . At the time of the slip, the same movement 

 took place in the neighborhood of this line as near AC, and A'C 

 was broken into two parts, A' B' and D'C ; the total slip, D'B', 

 being equal to DB. 



A third experiment was tried ; the left piece of wood was 

 shifted one-half inch and a straight line, A'C (fig. 5), was 

 drawn across it ; it was then shifted one-fourth inch more and 

 the straight line took the position A"C. When the jelly slipped 

 along the surface W, the line broke into two parts, A"B" , and 

 D"C ; the slip, D"B" , being equal to the total displacement of 

 the left side. Two characteristics of the movement in the last 

 experiment are to be noted ; the total slip on the ruptured surface 

 equalled the total relative displacement of the blocks of wood; 

 and at the time of the slip the blocks remained stationary, and 

 the whole movement was an elastic rebound of the jelly to a 

 condition of no strain. These two characteristics could have 

 been deduced from the elastic nature of the jelly without re- 

 course to actual experiment. It is also to be noted that the dis- 

 placements, measured from the line A'C, were greatest at the 

 fracture; that, on the right-hand side, they gradually diminshed 

 to zero at C ; that the displacements on the left side were much 

 greater than on the right ; and that they gradually decreased 



Fig. 5 



