188 © Conjectures concerning the Cause, and Observations 
4. If, however, it should stil! be supposed, notwithstanding 
these instances to the contrary, that there is some general con- 
nexion between earthquakes and the weather, at the time when 
they happen, yet, surely, it is far more probable, that the air 
should be affected by the causes of earthquakes, than that the 
earth should be affected in so extraordinary a manner, and to so 
great a depth; and that this, and all the other circumstances 
attending these motions, should be owing to some cause residing 
in the air. 
5. Let us then, rejecting this hypothesis, suppose that earth- 
quakes have their origin under ground, and we need not go far 
in search of a cause, whose real existence in nature we have cer- 
tain evidence of, and which is capable of producing all the ap- 
pearances of these extraordinary motions. The cause I mean is 
subterraneous fires. These fires, if a large quantity of water 
should be let out upon them suddenly, may produce a vapour, 
whose quantity and elastic force may be fully sufficient for that 
purpose. The oo facts, from which I would prove that : 
these fires are the real cause of earthquakes, are as follow: 
Srcrion I.—6, First, The same places are subject to returns 
of earthquakes, not only at small intervals for some time 
after any considerable one has happened, but also at greater 
intervals cf some ages. 
7. Both these facts sufficiently appear, from the accounts we 
have of earthquakes.; The tremblings and shocks of the earth ° 
at Jamaica in 1692*, at Sicily in 1693*, and at Lisbon in 
1755*, were repeated scmetimes at larger, and sometimes at 
smaller intervals, for several months. The same thing has been 
observed in all other very violent earthquakes. At Limat, from 
the 28th October 1746 to the 24th February 1747 (the time 
when the account of them was sent from thence), there had heen 
numbered no less than 451 shocks, many of them little inferior 
to the first great one which destroyed that city. 
S. The returns of earthquakes also, in the same places, at 
larger distances of time, are confirmed by all history. Con- 
stantinople, and many parts of Asia Minor, have suffered by 
them, in many different ages: Sicily has heen subject to them, 
as far back as the remains even of fabulous history can inform 
us of: Lisbon did not feel the effects of them for the first time 
in 1755: Jamaica has frequently been troubled with them, since ° 
the English first settled there; and the Spaniards, who were 
there before, used to build their houses of wood, and only one 
story high, for fear of them: Lima, Callao, and the parts ad-° 
* See the accounts of these in the Philos. Trans. 
+ See Antonio dUlloa’s Voyage to Peru, part i, book i. che. 
i Sce the place above quoted, 
jacent, 
