<i ———s'-.  -” 
27 
horizontal one ; also, the number of shocks in one locality varied 
enormously, 1,000 shocks a day have been recorded, whilst 
Calabria was affected by shocks for ten years after the great 
earthquake of 1783. The amplitude of vibration in a horizontal 
- direction varied from a fraction of a millimetre to about 70 mms. 
(three inches), the vertical amplitude being much less, never 
more than 10 mms. The velocity of the earthquake wave 
depended on the strata through which it travelled and the 
intensity of the shock and the distance from the origin, varying 
from a few hundreds to several thousand feet per second, The 
lecturer remarked that the characteristic sound which often 
accompanied an earthquake might be due to the folding and 
contortion of strata or by the rapid vibrations of the earth’s 
surface being communicated to the air and air waves being formed. 
The effect of earthquakes on land and sea were then described 
at length, such as faulting (the nature of which was explained 
by diagram), cracking of the earth, the overturning of buildings, 
the ejection of liquids and gases from fissures thus formed, the 
damming of rivers, and the stopping and starting of water 
springs, and the remarkable but terrible effects of the so-called 
tidal waves. Details of numerous examples to illustrate these 
effects were given. 
Slides were then shown of earthquake effects, some illus- 
trating cracking and even contortion effects on buildings, whilst 
others served to illustrate the destructive effects of recent earth- 
quakes at San Francisco, Valparaiso, and Kingston (Jamaica). 
A short account was given of the numerous mythological and 
pseudo-scientific explanations of earthquake phenomena—such as 
motions of mythical monsters within the earth, also supposed 
chemical effects, such as sulphur being burnt, imprisoned air, &e. 
At the present day only two theories held the field, and of these 
one seemed more or less dependent on the other, Before 
discussing these, Mr. Hora asked the audience to carefully 
examine Professor Milne’s map showing distribution of earth- 
quakes in space, and he projected the map on the screen, 
drawing special attention to the fact that, with the exception of 
the Alpine and South Himalayan regions, all areas of seismic 
activity corresponded with modern volcanic activity, and that the 
400 known volcanoes all lie within a distance of fifty miles from 
the sea coast, and lastly that the highest mountains as a rule 
faced correspondingly deep depressions in the ocean. He also 
drew attention to the varied nature of the ocean beds, the 
mountainous character of which seem to surpass that of the earth. 
Of these two theories, that of the explosion of steam within 
the crust of the earth, generally below the ocean bed near the 
shore, was hinted at by Aristotle, Lucretius, and Pliny, and 
definitely stated by Strabo ; it is alluded to by Shakespeare, but 
in modern times was put forward definitely by Mr. Robert Mallet 
