Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/84

Rh instant; but some of them affirmed they had first felt "una leggerissima trepidazione precedente," and that it was accompanied by a low sound, "pissi pissi," i.e., a sort of hum or buzz. With the exception of the suddenness, of the great sound, this was tantamount to the description given elsewhere. They spoke of but two great shocks, with the interval of about an hour between.

As regarded the time of the occurrence of the first; three public clocks were stopped by it—one of these being that of the Communal Campanile—and were stated all to have been arrested at a quarter past five, Italian time. They set all their clocks by sunset, and this Communal clock, was affirmed to be thus regulated, at frequent intervals, and to have been almost reliably correct. The first hour commenced (according to very common usage) at a quarter of an hour after the disappearance of the sun's disc. At some places, the immemorial usage, is to consider a quarter of an hour after sunset, the commencement of the first hour; at others half an hour after sunset; and at a few, sunset itself, commences the first hour.

Sunset took place at Vietri,on the 16th December, 1857, including refraction, that is, the sun's centre being apparently on the horizon at

and adding the sun's apparent vertical semi-diameter = 16' 17", to the zenith distance, = 1m 41s in time, we have for the moment of disappearance of the sun's upper limb

mean time at Vietri di Potenza.