Posted on June 15, 2020
There is this famous story about Benjamin Franklin going out into an electrical storm with a flag and a key - and doing the experiment that proved that lightning is electricity. The traditional date given for this story is June 15, 1752, but on the "On this day in history" and other websites I saw oodles of other nearby dates in June of 1752 associated with this experiment. Apparently we just don't know for sure the exact date.
The thing is, Franklin (whose formal education stopped at age 10) was very interested in electricity and had done lots of experiments. He suspected that lightning was electricity and had devised a plan to test the hypothesis (which is a kind of educated guess). He had already gotten all the materials he would need to safely run his experiment:
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This early Leyden jar
had a metal spike that was
in contact with water. |
a Leyden jar (which was a devise that could store an electrical charge)
a kite made out of a silk handkerchief
a hemp string, a silk string, and a length of wire
a house key
The wire was a sort of lightning rod that was attached to the top of the kite. The string attached to the kite was made out of hemp, and when it was wet it would conduct electricity easily. The idea was for Franklin to stand in the doorway of a shed, holding a silk string that was attached to the hemp string - the silk string would stay dry and so would not conduct electricity.
Of course, not just the silk string was attached to the hemp kite string, but a metal key was as well.
After readying the apparatus, Franklin waited for a thunderstorm. At his first opportunity, he and his son walked with all the materials into a field where there was a shed.
Franklin's son ran to get the kite aloft, and Franklin waited in the shed's doorway. He waited and waited, but nothing seemed to happen.
Then Franklin notice that loose threads of the hemp string were standing up - a sure sign of static electricity.
Remember, Franklin had studied electricity and knew what to look for. After seeing the hemp-string threads getting charged, he moved his finger near the key and felt a small jolt. He waited a bit and then moved his knuckle close to the key and saw a larger electrical spark jump from the key to his knuckle. (Of course, he felt that jolt even more!)
Awesome! Franklin had proved that the lightning we can see in the sky IS the same phenomenon we call electricity. He was able to store a lot of charge in his Leyden jar before he and his son returned home victorious.
Note that the kite-with-a-lightning-rod was picking up electrical charge just by flying high during a lightning storm. If his kite had actually been hit by lightning, Franklin might have been electrocuted! And if he died that day, who knows how that might have changed American history!
By the way, this story seems almost as if it would be "just a story" instead of reality. But it is true. However, some people report on the experiment using incorrect statements such as "Benjamin Franklin discovered electricity" - even though even ancient peoples knew about electricity. Also, some illustrations of the experiment are incorrect. Can you see the problem with each picture? (Answers below.)
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(Answers: Picture #1 - hmm, baby angels helped Franklin, instead of his son? Picture #2 - where's the shed? Picture #3 - it looks like lightning struck the kite and kite string in this picture! Yikes! Also, Franklin seems to be holding the same string as the key. The guy's a goner for sure!)
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