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Published online by Cambridge University Press: 01 May 2009
To the earthquake that ruined Lisbon on November 1, 1755, we may trace the great interest in the study of earthquakes which marks the middle of the eighteenth century, though valuable accounts of previous earthquakes had already appeared in the pages of the Philosophical Transactions. During the following year the Royal Society paid the same close attention to this earthquake that it did more than a century later to those of the eruption of Krakatoa. In 1757 an anonymous editor published The History and Philosophy of Earthquakes, in which he gave abstracts of ten memoirs by the “best writers on the subject”—Hooke, Woodward, Buffon, and Stukeley among them—followed by a summary of the observations on the Lisbon earthquake that had been communicated to the Royal Society. These are the principal sources on which Michell depended when he wrote his memoir on the cause and phenomena of earthquakes.
page 98 note 1 “Conjectures concerning the Cause and Observations upon the Phenomena of Earthquakes; particularly of that great Earthquake of the First of November, 1755, which proved so fatal to the City of Lisbon, and whose Effects were felt as far as Africa, and more or less throughout all Europe.” (Read 02 28, March 6, 13, 20, 27, 1760.) Phil. Trans., vol. li, 1761, pp. 566–634.Google Scholar
page 99 note 1 The above biographical details are derived chiefly from articles in the Dictionary of National Biography; the English Mechanic, vol. xiii, 1871, pp. 309–10; Knowledge, vol. xv, 1892, pp. 188–8; and Sir A. Geikie's Memoir of John Michell (Camb. Univ. Press), 1918.Google Scholar
page 100 note 1 Vol. lii, 1818, pp. 186–95, 254–70, 323–40.Google Scholar
page 100 note 2 Trans. Irish Acad. (read 1846), vol. xxi, 1848, pp. 58–60, 65–7, 84–5; also Rep. Brit. Assoc., 1850, pp. 17–19.Google Scholar
page 101 note 1 From records of the time of the great earthquake at Lisbon and more distant places, Michell estimates the velocity at more than 20 miles a minute. This is the earliest estimate of the kind known to me.
page 101 note 2 The following sentence is worth quoting from The History and Philosophy of Earthquakes (p. 26), as it refers to probably the earliest instance of a seismic experiment: “Honoratus Faber illustrates this doctrine by a variety of artificial earthquakes, as he calls them, confining gunpowder (a mixture of nitre, sulphur, and charcoal) in pits, and setting fire to it by a train.”
page 104 note 1 At the end of the section on stratification Michell gives the following paragraph: “Besides the rising of the strata in a ridge, there is another very remarkable appearance in the structure of the earth, though a very common one; and this is what is usually called by miners the trapping down of the strata; that is, the whole set of strata on one side such a cleft are sunk down below the level of the corresponding strata on the other side. If, in some cases, this difference in the level of the strata on the different sides of the cleft should be very considerable, it may have a great effect in producing some of the singularities of particular earthquakes.” One cannot help regretting the brevity of Michell's statement on the relations between earthquakes and faults. I can only suggest that, according to his view, the vapour, in travelling outwards by parting adjacent strata, would be suddenly arrested at the fault.
