72. OLDHAM: THE CACHAR EARTHQUAKE OF 10TH JANUARY 1889. 



being* corroborated by the fact that it lies right side up in its natural 

 position not having been overturned. "What seems to have taken place 

 in this case is as follows. During the first semiphase of the wave the 

 pillar was, by its own inertia, thrown over towards the north ; then, 

 before it had fallen very far, the base was rapidly thrust backwards, 

 and thus a thrust was communicated through the pier to its stone 

 cap, by which the latter was thrown off towards the north or in the 

 direction from which the shock came. The next question to determine 

 is the angle that the line in^which it was projected would make with the 

 horizon. The line of motion of the top of the pillar would be complicat- 

 ed, for, in the first place, it would be moving in a circle due to the 

 overturning of the pillar, and, in the second place, the movement impress- 

 ed on it by the earth- wave would tend to cause it to travel in a 

 straight line parallel to the direction of emergence at this point, and its 

 actual line of motion would be produced by the combined action of these 

 two causes. Thus, as far as the motion in space of the summit of the 

 pillar goes, it would tend to throw the cap downwards at a greater angle 

 with the horizon and with a greater velocity than that of the wave- 

 particle ; but as brickwork will not permit of the passage of stone 

 through its substance, it is evident that the cap cannot have been shot 

 off at a greater angle with the horizontal than that made by the upper 

 surface of the pillar at the moment of projection. Now during the 

 short time that intervened between the first and second semi-phases of 

 the wave, the pillar could not have fallen over very far, and consequent- 

 ly the upper surface could not have been greatly inclined from the hori- 

 zontal ; further, as there does not seem to have been much adhesion 

 betw r een the pier and its cap, it is evident that the former could not have 

 pulled the latter after it downwards to any great extent, so that little 

 but the horizontal component of the shock would be communicated to 

 the cap. The direction, therefore, in which the cap was projected may 

 be taken as being as nearly as possible horizontal, and its velocity as 

 that of the horizontal component of the velocity of wave-particle. 



Taking the body as projected horizontally, and calling b the vertical 



( 72 ) 



