he earthquake, or better said the seaquake, of All Saints’ Day of 1 November 1755 at Lisbon was felt in three different continents, namely Europe, Africa and America. The ensuing tsunami was observed in Europe, in Africa, on the Azores and Madeira, and even in the Antilles and the eastern coast of America. Later observations showed in the whole of Europe the presence of “seiches”, i.e. fluctuations of the water surface due to the seism. The authors have considered the meteorological conditions at the moment of the earthquake and suggest here a new interpretation of the appearance of a yellow fog or smoke and the foul smell of sulphur namely as a consequence of the eruption of Katla volcano in Iceland a fortnight before. This interpretation is confronted with the then dominating theory of Aristotle’s Meteorologica or with prognostications from the Bible. Nevertheless, other accounts testify the emerging new vision of scientific ideas in the spirit of the Enldightenment