Lightning Page 140

to exist a potential, the exact magnitude of which is yet to be determined, beyond which air breaks down a little at a time.

As charges accumulate in the lower portion of a thunderhead, equal and opposite charges are produced by electrostatic attraction in the ground and all grounded objects below. As the potential passes the breakdown level, "leader strokes" begin probing their way toward the opposite charge. Usually the leaders start from the cloud, but sometimes from the ground. Advancing 50 to 60 yards at a time, and pausing about 100 microseconds between steps, the leader works its way toward the opposite charge. Then current flows, a small stroke dissipating as much as five kilowatt hours, and a large stroke, many times more.

A lightning discharge, like any electric current, follows the path of least resistance which is almost never a straight line. The potential gradient from a cloud to the ground is constantly being distorted by the turbulence of the atmosphere. On the ground, moisture, temperature, and the varying quality of the ground itself play important roles in determining the path of a stroke. With all these variables, lightning has been observed to do some pretty strange things. A neighbor of mine had her house struck. The bolt travelled down a drainpipe, followed the electrical wiring across the