So many pages have already been given to this interesting earthquake that I must sketch still more briefly my own view as to its origin. There were, I believe, two distinct foci with their centres about twenty-four miles apart along a north-west and south-east line, and it was to this arrangement that the elongation of the meizoseismal area was chiefly, though not entirely, due. The evidence is insufficient to determine whether the earthquake was caused by fault-slipping; it is in no way opposed to this view, but if the Neapolitan earthquake stood alone, we should hardly be justified in drawing any further inference. Relying, however, on knowledge obtained from the study of more recent shocks, it seems to me probable that the two foci formed parts of one fault with a general north-west and south-east direction. The slip causing the first part of the double shock apparently took place within the south-east focus, and was followed after a few seconds by one within the north-west focus, greater in amount as well as more deeply seated. In consequence of these displacements there were local increases of stress, causing numerous small slips within or near both principal foci; and, if we may judge from some slight shocks felt at La Sala, accompanied also by other minor slips in the intermediate region of the fault. REFERENCE. MALLET, R.--_The Great Neapolitan Earthquake of 1857: The First Principles of Observational Seismology_, etc. 2 vols 1862. FOOTNOTES: [3] _Irish Acad. Trans._, vol. xxi., 1848, pp. 51-105 (read Feb. 9, 1846). [4] _Brit. Assoc. Reports_, 1850, pp. 1-87; 1851, pp. 272-330; 1852, pp. 1-176; 1853, pp. 117-212; 1854, pp. 1-326; 1858, pp. 1-136. [5] _A Manual of Scientific Enquiry_, edited by Sir J.F.W. Herschel, 1849, pp. 196-223. [6] _Irish Acad. Trans._, vol. xxii., 1855, pp. 397-410. [7] The linear dimensions of the isoseismal lines are obtained by measurements from Mallet's maps. The areas are given by him in geographical square miles. [8] Mallet, by some accident, omitted the losses at Polla and neighbouring towns from this estimate. Mercalli (_Geologia d'Italia_, pte. 3, p. 324) gives the number of killed as more than 12,300. [9] Mallet does not make use of the term _epicentre_; he speaks of the line FE as the _seismic vertical_. The modern and accepted terms are used above [10] _Japan Seismol. Soc. Trans._, vol. xi., 1887, pp. 175-177. [11] _Ital. Seismol. Soc. Boll._, vol. ii., 1896, pp. 180-188. [12] Professor Omori gives the mean direction as S. 71° W., but this was obtained from observation on lamps with square, as well as with circular bases. [13] Twelve measurements chosen at random from Professor Omori's list gave a mean direction of S. 78° W. [14] When the accuracy of all the observations seemed equally probable, he adopted the mean of the two extremes as the true direction.