Ben Franklin never officially wrote up his experiment.
The kite had a metal spike on top to discharge the electrical charges in the air.
If lightning had struck the kite, the string would be burned or Ben would have been electrocuted by the lightning.
He probably flew the kite in the early stages of the storm when he thought he was safe from lightning.
The experiment's purpose was to determine what lightning was made of. He determined it was made of electrical charges and not fire. This meant he had a way to postulate how storms behaved. (Although today we are not sure about every part of a storm's life span.)
The key was used as an indicator of electricity. It glowed due to corona discharge. It also shocked him.
He held onto a dry, 6 inch, silk ribbon to act as an insulator between himself and charges on the key.
He flew the kite from indoors or at the very least from a doorway –under dry cover.
Do not try Franklin's kite experiment. The odds are very high that you will get struck by lightning and die. A high electrical build up can even occur on a day when there no storms to be seen.
Much more is discussed in the class notes.
Corona discharge is the glow at the sharp edges of an electrified object. Below are some keys that have been electrified.
When this glow occurs on the masts of sailing vessels, it is called, "St. Elmo's Fire." More in the class notes.
by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)