Thunderstorms and lightning are produced by the ignition or explosion of sulfurous, nitrous, or other combustible vapors in the atmosphere.

Lightning once belonged as naturally to chemistry as it does to electricity today.

Drawing on older traditions, many eighteenth-century scholars imagined the atmosphere accumulating combustible sulfurous and nitrous vapors. Their spontaneous ignition or explosive reaction could explain lightning, thunder, heat, and the smell associated with storms. Similar subterranean vapors were invoked for earthquakes and volcanoes, linking several violent natural phenomena through one chemical framework.

The theory was not obviously foolish within contemporary chemistry. Sulfur really burns dramatically. Combustible vapors exist. Electrical phenomena themselves were poorly understood and were sometimes described using fire-like or sulfur-like language.

Experiments gradually reorganized the problem. Benjamin Franklin proposed that lightning was electrical and developed tests involving pointed conductors, insulated rods, and later the famous kite experiment. Similar experiments in Europe drew sparks from storm clouds. Lightning rods provided a practical technological consequence: if lightning behaved like electricity, charge could be intercepted and conducted.

The old chemical theory did not vanish instantly. Some scholars tried to combine combustion and electricity, but atmospheric electricity became the dominant framework.

Modern lightning research still studies a surprisingly difficult question: exactly how a storm’s electric fields initiate a lightning channel. The mechanism is electrical, not the ignition of sulfurous vapor.