Benjamin Franklin discovered that lightning was caused by electrical discharges from clouds, and he is credited with inventing the lightning rod. Almost three centuries later, high-speed photography in the twenty-first century has revealed precisely how a lightning discharge happens, and it is much more complex than previously thought. Slowing down the flash observed by the human eye revealed that normally unseen negatively charged branches, called leaders, fork their way from the cloud towards the ground. Meanwhile, positive leaders grow upward from high places, like lightning rods.
