190 EARTHQUAKES. 
When we recollect, however, that the inductive basis 
of our knowledge relating to the nature and causes of 
earthquakes, rests upon our knowledge of chemistry, 
geology and physical philosophy, which are practically 
the creations of the present century, it is less strange, 
than it might at first appear, that we possess so little ac- 
curate information about these convulsions of the earth. 
Passing over the fanciful explanations of many an- 
cient writers relating to the motion of earthquakes, we 
find that Travagini, in 1679, first entertained the 
thought that an ‘‘earthquake was a pulse-like motion 
propagated though solid ground.’ Hooke, in 1690, 
divided the phenomena into different genera according to 
the effects produced in elevating, depressing, transport- 
ing or transforming the earth’s surface or crust. 
Woodward, in 1695, thought that earthquakes followed 
from the contact of water with fire in the interior of the 
earth. Priestley connected them with electrical phe- 
nomena, while Mitchell, in 1760, thought they came 
from the impact of asubterranean liquid mass, breaking 
in waves upon the thin, flexible crust of the earth, which 
was contorted and thrown into folds as a ‘‘carpet is 
thrown into undulations when shaken.” 
Mitchell did not, however, comprehend the true prin- 
ciples of wave motion, and hence could not satisfacto- 
rily explain the reason why large areas were almost sim- 
ultaneously disturbed. 
It remained for Sir Thomas Young, in 1807, to indi- 
cate that the real nature of earthquake motion was vi-. 
bratory, and was ‘‘ propagated through the earth nearly 
in the same manner as a noise is conveyed through the 
elie?” 
To know the true nature of earthquake motion is of 
first importance—for it is only as we are able to trace 
these phenomena to their starting place, that we are 
able to formulate a theory as to their producing cause. 
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