Benjamin Franklin
Is lightning divine anger, or electricity?
That time, that place
A printer, a politician, and largely self-taught. In his day lightning was still close to a punishment from above. Bell-ringers were regularly killed trying to drive storms away by ringing church bells.
Why this question
A laboratory spark and a lightning bolt resemble each other in many ways: the crack, the smell, the jagged path, the melting of metal.
If they are the same thing, then the terrifying one becomes something you can handle.
What was found
The kite experiment is famous. Whether he performed it himself is disputed; what mattered came after.
If they are the same, it can be led away. Stand a pointed metal rod on the roof and run a wire to the ground, and lightning takes that path instead of the building. The lightning rod.
An idea became an object, and the object saved lives.
He treated electricity not as two fluids but as one thing in surplus or deficit, calling the surplus positive and the deficit negative. Which side to call surplus was a coin flip, and he chose the opposite of what turned out to be the case. That is why conventional current runs opposite to the actual motion of electrons.
Lightning was a punishment sent from above
The properties a laboratory spark shares with lightning
The rod spread fast — though some opposed it as interfering with divine will