62 OLDHAM : THE CACHAR EARTHQUAKE OF 10TH JANUARY 1869. 



the direction of wave-path had made so obtuse an angle with that of the 

 end walls it is difficult to believe that they would have fallen so directly 

 outwards without the slightest obliquity; but if we imagine the shock 

 to have come from the north, or slightly west of north, a direction which 

 would accord with the observations elsewhere, this difficulty disappears, 

 and further the apparent anomaly of a very instable body being over- 

 thrown towards a point from whence the shock could not possibly have 

 come is explained. Supposing the direction of emergence of the wave to 

 have been from the north, it would make an angle of about 30° with the 

 direction of the side walls ; this would, of course, tend to make the walls 

 rock in a north and south direction, while their shape and position would 

 cause them to rock easiest east-north-east and west-south-west, the ac- 

 tual direction in which they swung being compounded of these two 

 motions ; the obliquity of the shock prevented its overthrowing the walls 

 during the first semiphase but if the wave-period corresponded at all 

 with the period of vibration of the wall as an inverted pendulum, its 

 swing would be increased during the second semiphase; and this, combined 

 with the already weakened state of the wall, would throw it over beyond 

 possibility of recovery ; the diagonal swing induced by the action of the 

 earthquake-wave would have loosened the bricks, and so the fact is ac- 

 counted for that the bricks of the side walls were all separated while 

 those of the end walls still adhered to each other, though the wall 

 as a mass was fractured in its fall. The end walls being much nearer 

 normal to the direction of the shock were overthrown with greater 

 facility, though there is no evident reason for their being thrown 

 in opposite directions, and not both towards the same point ; this was 

 probably due to the presence of the chimney stack at the north-wetsern 

 corner ; this stood firmer thau the unsupported north-eastern corner and 

 so during the first semiphase the north wall was, as it were, stretched, 

 and so, being to a certain extent deprived of support, was overthrown 

 easier than the south wall where both ends swinging over equally it was 

 more fully supported, and then, gaining impetus during the second semi- 

 phase, was precipitated outwards. These considerations show that much 

 ( 62 ) 



