'—* 
Evie 
WILLIAM G. STEVENSON. OS 
bed of rock to another of a different character, is par- 
tially or wholly reflected ; and, in proportion to the 
amount of reflection or interference, is the shock les- 
sened: some small portions of earth being free from any 
shock or movement, while all around. the vibrations are 
distinctiy and destructively felt. 
Itis said that ‘‘the Temple of Diana at Ephesus was 
built on the edge of a marsh, in order to ward off the 
effect of earthquakes ;’’ and we are told by Pliny that 
the Catacombs have protected the Capitol of Rome: 
while others state that the Romans discovered the pro- 
tecting influence of caverns, deep wells, and quarries 
against earthquake violence. There is no doubt but the 
principle therein involved is a correct one. The vibra- 
ting wave-impulse is interrupted, because the continuity 
of the medium through which it passes is broken, and 
‘the force of the impulse is spent upon the margins of 
the caverns or ravines the same as it would be upon the 
face of a cliff or scarp were it in the course of the vibra- 
tory movement. The points of wave-interference are 
the places of greatest shock and danger. 'The laws of 
motion are the same whether they apply to air, water, 
or earth-waves. 
The duration of an earthquake varies from a minute 
to many days, or even months. ‘‘In Japan, A. Dv. 745, 
there was a shaking which is said to have lasted sixty 
hours ; and, in A. D. 977, there was a series of shakings 
lasting three hundred days.’’ Prof. Milne further re- 
ports that at San Salvador, in 1879, more than six hun- 
dred shocks were felt within ten days; in 1850, at Hon- - 
duras, there were one hundred eight shocks in a week, 
and two hundred shocks in a single day at Lima, in 
1746 ; and two hundred eighty-three shocks were felt in 
ten hours, at St. Thomas, in 1868. 
The number of shocks experienced at Charleston, 
August 31st of this year, is, therefore, in no way ex- 
7avs 
