120 EARTHQUAKES. 



influence, the preponderance of shocks during autumn is particularly observable. Nor is this 

 peculiar to the tremors alone ; for of the fifteen great earthquakes since 1570 which have been 

 mentioned, two were in February, one in March, three in April, three in May, two in July, one 

 in September, one in November, and one in December ; or, distributed in seasons, there were 

 seven in autumn, three in summer, and two each during spring and winter. 



But because the earth does not evolve heat or moisture to produce sensible effect on the 

 atmosphere, and thus announce the agitation shortly to occur, it by no means follows that the 

 aerial strata in contact with it are not disturbed at such agitation, and that an extraordinary 

 meteorological state does not ensue, explicable only as a consequence of the earthquake. Ordi- 

 narily rain falls in central Chile twice in nine years, between the close of October and com- 

 mencement of April ; yet there has been but one great earthquake not soon followed by a rain- 

 storm, and, on that occasion, clouds and vapors (altogether unusual in December) wholly 

 obscured the sun for days. Deluges of rain, with excessive lightning, followed also the 

 Catania, Lisbon, and Calabria earthquakes. 



The occurrence of luminous meteors about the times of the shocks seems pretty well authen- 

 ticated in Chile, as well as elsewhere. They were seen before the Catania earthquake of 1693.* 

 During the remarkable one in New England, 29th October, 1*727, persons of credit affirm that 

 they perceived flashes of light before the shock ;f at Lisbon they were perceptible on the sides 

 of the near hills at the third shock ;J in Calabria, during the commotion; and in Chile, some- 

 times before, though most generally after it. We are, therefore, authorized to infer that 

 unusual electrical disturbance is, at least, a consequence of the phenomenon. That it is the 

 cause, has been argued by more than one philosopher, more especially at the period when our 

 illustrious countryman established the identity of lightning and electricity. In an account of 

 the earthquakes which occurred in England in 1750, published by Dr. Stukely in the Philo- 

 sophical Transactions for that year, after referring to a discourse on electricity by Franklin, 

 he goes on to argue that, " on the same principle, if a non-electric cloud discharges its contents 

 on any part of the earth when it is in a highly electrified state, an earthquake must, of neces- 

 sity, ensue." This theory of its origin serves him to explain why shocks are simultaneous over 

 such extended tracts, and also why they are most violent in rocky countries. A like hypo- 

 thesis is suggested by Dr. Donati, the professor of botany at Turin. Others, as Dr. Martin 

 Lister, regarded the material cause of thunder and lightning and earthquakes as the same, viz: 

 "the inflammable breath of the pyrites; the difference is, that one is fired in the air, the other 

 under-ground;" and when we remember that there are no electrical displays in the atmosphere 

 west of the Andes, we need not be surprised that many in Chile and Peru, notwithstanding the 

 mass of testimony in favor of volcanic origin, continue to believe that equilibrium is thus restored. 



Buffon's supposition, that they were attributable to the falling in of caverns existing in the 

 interior of the globe, is pronounced, by geologists, || only admissible under one of two conditions: 

 such cavities must either have been formed at the original cooling of the earth, and, therefore, 

 would not be likely to sink at the present day ; or they could only have been created by subse- 

 quent convulsion, implying, in itself, volcanic agency. Their connection with volcanoes is 

 shown by multitudes of isolated facts, that might be quoted from many writers ; though only 

 Humboldt and Darwin have enumerated series of events tending to establish it. The former 

 selects the earthquakes of 1811-'12, the latter that of February, 1835; prior to recapitulating 

 which, from their writings, three or four individual instances may be mentioned, of more than 

 ordinary interest because of the magnitude of their consequences. 



On the 29th September, 1759, after eighty days of earthquakes and subterranean thunders, 

 the volcano of Jorullo (Mexico) burst out, increasing the height of its crater nearly 1,700 feet, 

 and elevating 24 to 30 square miles several feet above the surrounding plain. Vesuvius exhi- 



* Philosophical Transactions, Vol. XVII. t Ibid., Vol. XXXIX. t Ibid., Vol. XLIX. Ibid., Vol. XIV. 



|| Daubeny: On volcanoes. Second edition, 1844. 



