Kite Experiment – Benjamin Franklin Historical Society

On June 10, 1752, Benjamin Franklin tested the lightning conductor with his kite-flying experiment. An excerpt from the article:

"Flying a kite in a storm was perhaps Benjamin Franklin’s most famous experiment that led to the invention of the lightning rod and the understanding of positive and negative charges. The connection between electricity and lightning was known but not fully understood. By conducting the kite experiment Franklin proved that lighting was an electrical discharge and realized that it can be charged over a conductor into the ground providing a safe alternative path and eliminating the risk of deadly fires.

Erecting iron rods

Franklin hypothesized that lightning was an electrical discharge. Before he thought of conducting his experiment by flying a kite, he proposed erecting iron rods into storm clouds to attract electricity from them. He also suggested that the tips of the rods should be pointed instead rounded so that they could draw electrical fire out of a cloud silently. Franklin speculated about its usefulness for several years as he was unable to perform his experiment since he thought it had to be conducted from a higher ground. Philadelphia has a flat geography and at the time there were no tall structures, he was anxiously waiting for the construction of Christ Church that was being built on a steeple to conduct his experiment.

Franklin wrote his proposal for the iron rod experiment in a letter to Peter Collison who was a member of the Royal Society of London. Collison presented Franklin’s hypothesis to the Society who ridiculed and laughed at his idea failing to recognize its significance. A year later when the French translation was published it attracted the interest of French scientists Delor and Dalibard, who separately and successfully conducted Franklin’s experiment calling it the “Philadelphia experiment”.

Franklin was recognized by the Royal Society of London and in scientific circles all over Europe, becoming the most famous American in Europe.

Flying a kite

Franklin had not heard of the success of his experiment in Europe before he conducted the same experiment with a kite. One day in June 1752, it occurred to him that he could test his hypothesis by flying a kite instead of waiting for the church to be built. With the help of his son William he built the body of the kite with two crossed strips of cedar wood and a silk handkerchief instead of paper as it would not tear with wind and rain. They attached a foot long sharp and pointed wire to the top of the kite as a conductor and at the bottom end of the string where it is held they attached a silk ribbon and a metal key. A metal wire connected the key to the Leyden Jar.

Franklin kept dry by retreating into a barn; the end of the string was also kept dry to insulate himself. When the stormed passed over his kite the conductor drew electricity into his kite. The kite was not struck by lightning but the conductor drew negative charges from a charged cloud to the kite, string, metal key and Leyden jar. It appears that he knew enough about grounding to protect himself from being electroshocked. When he moved his hand near the key he received a shock because the negative charge attracted the positive charge in his body."