The International Discourse

The introduction of the lightning rod or at least the discussion of it was sometimes helped by an extreme weather event. The summer of 1783 certainly saw one of those. On 8 June, in the south-east of Iceland, the Laki volcanic fissure erupted. It was the start of an eight-month-long series of violent explosions which threw up such enormous clouds of ash that much of the northern hemisphere was affected. In large parts of north-western Europe the haze was anxiously observed as dry mist, dry fog or Höherauch. Many scholars regarded these evil vapours as the main cause of the extreme summer heat and the subsequent extraordinary frequency of thunderstorms that year.

Some also believed that there was a more direct relationship between those two natural phenomena. According to an early modern theory that can be traced back in part to Aristotle (384-322 BCE) and Heraclitus (ca. 500 BCE), thunderstorms were caused by the spontaneous combustion of sulphurous and nitrous vapours in the air. It was a tenacious concept that in the second half of the eighteenth century still had a wide group of supporters, including the internationally renowned Petrus van Musschenbroek himself, though he based his defence of it on the Bible rather than the classics – after all, it was also by a rain of burning sulphur that the godless city of Sodom perished.