THE POSITION AND EXTENT OF THE SKISMIC VERTICAL. 61 



other points of great interest, it becomes a matter of much importance 

 that we should be able to fix its position with accuracy. 



In the case of this earthquake we cannot, unfortunately, obtain 

 such a large number of observations mutually confirming- each other, as 

 was the case in the great Neapolitan earthquake of 1857, which has 

 been so ably described by Mr. Mallet; but when we consider the circum- 

 stances of the case, it is not surprising that the number of trustworthy 

 observations is so few. In the first place, there was not the same 

 number of towns with their concomitants of numerous buildings whose 

 injuries would point out the direction of wave-path. The native huts 

 being wretchedly built, and mostly of mats, could give no evidence at 

 all, and the masonry or brickwork buildings, which could give any indi- 

 cations of value, were few and far between. Then, again, the disturbed 

 state of the country, which, allowed of but a small portion of the 

 seismic area being visited, combined with the fact that at the point 

 nearest to the seismic vertical which could be visited, it was nearly 

 50 miles distant; — all tend to diminish both the quantity and the quality 

 of the evidence obtainable. 



But as no one now doubts that an earthquake is a wave of elastic 

 compression originating in a definite region, and spreading from it 

 through the crust of the earth, we no longer require a great weight of 

 evidence to prove the existence of a seismic focus and a seismic vertical ; 

 and consequently the few observations obtainable, which certainly agree 

 very well with each other, will be sufficient for the present purpose. 



Before tabulating the observations and pointing out the position of 

 the seismic vertical, I shall discuss some of the observations which have 

 as yet been only casually noticed or omitted altogether. 



In the first place, I shall take the sawmill at Kochela, a sketch plan 

 of which is given on PI. VII ; at the first glance it would seem as if 

 the direction here had been N. 40° E„ being the direction in which 

 the piers of the side walls have been thrown. A comparison of this 

 with the observations at other places, and a more careful inspection of the 

 plan itself, throw much doubt on this conclusion. In the first place if 



( 61 ) 



