14 
president’s address. 
chalk, sands, clays, &c., which overlie them. It is known that 
the superincumbent rocks are mncli thicker in the south-east 
of England, in the district of the Weald of Kent, and it is 
possibly owing to this circumstance that only very few records 
of observations of the shock from that district are forth¬ 
coming. From this cause, too, may arise the double shock 
noticed in many places ; the first being due to the more 
rapidly transmitted wave in the harder, the second to the 
slower one in the softer rocks. 
It was noticed that the cracks in the walls of buildings 
were at an angle of about 30°, while in the chimneys this 
was increased to 40° or 45°. In one of the churches two 
cracks, at angles of. 32° in opposite directions, met over the 
door. One house was rent spirally, and the observation of 
chimneys having been twisted was made in several instances; 
in one case the side that had been to the south was facing 
almost south-east. Whether this twist is due to an actually 
changing direction of the shock or to the centre of gravity 
of the building not coinciding with the centre of figure is 
still undecided ; the more general opinion being the former, 
while Mr. Mallet holds the latter. That there was more 
than one shock is made probable by the fact that one man 
described the movement which he felt as being like “ three 
seas.” There is also a good deal of evidence of varying 
direction in places quite near each other ; but this may very 
probably be due to the damage having been done in the one 
case by the direct throw and in the other by the backward 
movement. Altogether it seems probable that the shock 
originated a short distance to the south-east of the village of 
West Mersea, where, emerging nearly vertically, it did but 
little damage, and travelled outwards from that centre with a 
velocity and a violence dependent upon the nature of the 
material through which it was propagated. At Kew, the 
magnetographs recorded the shock, and from the fact that 
the magnets which showed tlie greatest disturbance were 
those which lie east and west, it was inferred that the shock 
was more nearly north and south than at right angles to this. 
The interest awakened by this occurrence in earthquake 
measuring in general produced a series of papers in “ Nature,” 
Yol. XXX., on the subject, to which I may refer any who 
would like further information. Our own little tremors 
seem, however, scarcely worth mentioning by the side of the 
terrible disturbance in 'the south of Spain, where so many 
lives have been lost—as many, perhaps, by privation and 
exposure to most unusually inclement weather as by the 
actual fall of the buildings in the towns and villages destroyed 
by the earth movements. 
