In ancient times, lightning was seen as a tool of the gods. In Viking legend, it was Thor’s hammer striking an anvil in the sky that was responsible for lightning. For the Greeks, it was Zeus who threw lightning down to the earth. North American Indian tribes thought that lightning was produced by a mystical bird with flashing feathers whose flapping caused thunder. Even now, hundreds of years after the first scientific work with lightning, people remain in awe of its power. In the 18th century, the first systematic scientific study of lightning was carried out by Benjamin Franklin. Before Franklin’s experiments, electrical science had grown to the point of separating positive and negative charges, and had developed primitive
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In 1752 Franklin found success during a Pennsylvania thunderstorm. When a storm cloud passed over his kite, sparks flew from a key tied to the bottom of the damp kite string. He was also able to collect a charge on a Leyden Jar, which was a simple capacitor, that was connected to the key via a thin metal wire. Using this he was able to determine that the charge was negative. Franklin was not affected by the charges thanks to an insulating dry silk ribbon that connected the kite string to Franklin’s hand. Upon reaching out to touch the key, the negative charges were attracted so strongly to the positive charges in his body that a spark jumped to Franklin’s hand. Many who have attempted to duplicate Franklin’s experiment have died trying.
Rain clouds become charged through a complicated and largely unknown process. There are two major categories of hypotheses that describe the process: those that include ice as a key factor and those that do not. The ice hypothesis holds that the charges are a result of the separation of ice and water droplets within the cloud, as experiments have shown that freezing a dilute solution of water causes the ice to gain a negative charge and the water to keep a positive charge. Inside a cloud, rising air pulls small droplets of water up and away from the larger falling ice particles, causing the upper half of the cloud to gain a positive charge and the lower half to gain a negative charge. Other