The day before the catastrophe of Port-Royal, the weather was remarkably serene and clear. In that most dreadful earthquake, 1692, of Sicily, where 54 cities and towns, beside a great number of villages were destroy'd; but especially the whole city of Catania; It was preceded by a most agreeable, serene and warm season, which was the more observable on account of its being unusual at that time of the year.
I have been inform'd, that in the morning of both earthquakes last past with us, the air was serene and calm; on the morning before that 8th of February, the air was observ'd to be remarkably calm; and that a little before, a black cloud appeared over great part of the horizon. Dr. Hales in his relation, says, the Centinels in St. James's Park, and others who were abroad in the morning of the last earthquake, observ'd a large black cloud, and some coruscations, just before the shock, and that it was vary calm weather: And that, in the history of earthquakes, they generally begin in calm weather, with a black cloud.
This observation includes the suspicion of earthquakes arising from tumults and commotions in the upper, or under region of the air. The remarkable clearness of the air before earthquakes, observ'd by all, shows evidently how free it is from vapours and the like.