Ben Franklin's Kite

What exactly was this experiment of his and why wasn't he killed?
The following is a letter to a friend from Franklin, describing the experiment:

circa June 1752
"To the top of the upright stick of the (kite's) cross is to be fixed a very sharp pointed wire, rising a foot or more above the wood. To the end of the twine, next the hand, is to be tied a silk ribbon, and where the silk and twine join, a key may be fastened. This kite is to be raised when a thunder gust appears to be comming on, and the person who holds the string must stand within a door or window or under some cover, so that the silk ribbon may not be wet; and care must be takin that the string does not touch the frame of the door or window. As soon as any of the thunder clouds come over the kite, the pointed wire will draw the electric fire from them, and the kite, with all the twine, will be electrified, and the loose filaments of the twine will stand out every way, and be attracted by an approaching finger. And when the rain has wet the kite and twine, so that it can conduct the electric fire freely, you will find it stream out plentifully from the key on the approach of your knucle. At the key the phial (a device for storing charge, an early form of a capacitor) may be charged, and from electric fire thus obtained, spirits may be kindled, and all the electric experiments performed, which are ussually done by the help of the rubbed globe or tube, and thereby the sameness of the electric matter with that of lightning completely demonstrated."

 

More can be found at http://www.ushistory.org/franklin/kite/index.htm. (The animation at the top of the page is off. Ben Franklin did not experience a lightning strike.)

In Europe G.W.Richmann was killed in trying to repeat the Franklin's experiments - so don't you try it, even with Franklin's precautions!!!

Why did he do what he did?

The pointed wire was to provide a sufficiently high electric field that enough current would be attracted to to allow Franklin to do his experiments. (The sharper the object, the greater the electric field is around it.) The silk ribbon was to act as an insulator between himself an the wet conducting twine. The key provided several sharp points for visible discharge of the electron current descending the twine.
Often Ben Franklin is pictured doing this experiment during a lightning storm. But he wasn't that stupid. A lightning strike to the kite would have destroyed the kite the twine, and possibly Ben Franklin, regardless of the piece of silk. The dry silk loop did keep the prevent any collected charges from coming to him. In actuality Franklin probably flew his kite before the full storm arrived.

 

What did it show?

After collecting the cloud's charge, Ben Franklin performed a series of experiements which showed that the charge from the clouds behaved in the same manner and negatively charged bojects. This was scienctific evidence that lightning comes from electricity and is not fire. once it was established that lightning comes from electricity it can try to be explained. However, not much progress was made in explaining the source of lightning for about another 100 years.