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Voiceover: So in the last couple of videos, we've talked about Benjamin Franklin as a printer, we've talked about him as a successful public leader, as a successful businessman, but we also know Benjamin Franklin, and we've talked about him as a successful writer, with Poor Richard's Almanac, but there's this other side of Benjamin Franklin which kind of makes him larger than life, which he was also a significant scientist. Voiceover: Yes, you know, he would have thought it was strange that you could aspire to be a great citizen and not care about science. Back then, you should know about science. So he did everything from tried to track the gulf stream, he discovered ways to use dark fabrics to absorb heat, he creates the great Franklin stove, a fireplace that's a wonderful way to be more efficient in terms of heating a room without getting it all smoky, and... Voiceover: And also not wasting the heat I think, normally in a fireplace all the heat goes straight up, and out. Voiceover: Right, and it sort of had a nice little top to it, a little plate, that got very hot, and so he was a very practical inventor. Even things like bifocals, he's riding along the road one day, and he keeps wanting to read, but then look up into the distance, and he says, "Well, why don't I have two pieces "of glass melded together, one that's good "for reading, and one that's good for looking out in the distance." So, it wasn't like he was a research scientist, he was just a practical inventor. What makes him into a great research scientist is when finally, in the 1740s and early 1750s, he starts doing the electricity experiments. Voiceover: And this is important, this is actually something I learned when I read your book on Benjamin Franklin, is that, I mean this was real, as you mentioned, this was real research. This was something that, understanding the nature of elecricity, the nature of lightning, and how to manipulate it. Voiceover: Yeah, we think of him as a doddering old dude flying a kite in the rain, but in fact, those electricity experiments were the most important experiments of that era. Not only for the practical use of them, but for the theory. Up until then, people had created static electricity, you know, when you rub your sweater against a piece of glass, and lots of sparks come out, and they thought that electricity was two different fluids, and they had two different names for the fluids. Franklin realizes it's a single fluid, and he creates the idea of positive and negative, plus and minus, those type of things, so that it's a flow of electricity, and he does that with his electricity experiments that really begin in the 1740s, partly as a parlor trick, 'cause he loves it, but then he realizes, no, let's study this stuff - electricity. Voiceover: And it was a real issue, I mean people were dying because of lightning. I remember in the book, there was a particularly funny, I forgot the exact quote, where he said, "Churches get to be, tend to be hit "disproportionately, so it seems like God "is not favoring them." (laughing) Voiceover: Right, well you know what they used to do, was they would sanctify the church bells, so that it would ward off the lightning, and they would even sometimes store gunpowder inside churches with sanctified bells. But the lightning kept hitting the steeples of the churches, and people in Germany, Italy, and then the United States, there were these huge explosions, lightning was the great scourge of the times. Voiceover: So to ward off lightning, they would sanctify a metal bell, and put it at the top of the tower. Voiceover: Bingo! (laughing) It did not work! And Franklin has a wonderful line in one of his letters which is, "You'd think we would try something different, and see if that worked." (chuckling) And so Franklin looks at sparks, that he's been looking at from his electricity experiments, and he's been creating these little sparks with the static electricity, but then using wire to make it into a flow of electricity, and put it into a battery. He gives us the name "battery" 'cause he puts it together a lot of Leyden jars, which is the way they used to store electricity. And so he's looking at the similarity between sparks and lightning. And in his notebook, he makes a little chart. He said, well sparks have these qualities, they're fast, they jump, there's a sulfurous smell, they make a little crack, and lightning has the same qualities. And he does a wonderful notation at the bottom of that notebook page, very scientist-like, he says, "Let the experiments be made." And that's how you get the lightning experiments. Voiceover: He literally, it's a little bit of a legend now, but he literally did go out into a rainstorm and tie a kite with a silk thread, to a kind of a key attached to a Leyden jar? Voiceover: Well, what he did was as clouds were passing over, he and his son William went out into a field, and as the rain started, they flew the kite, and they tried to draw the electricity down from the clouds, 'cause it was his theory that a lightning strike was just a spark coming out of a cloud. And at first it didn't work, but as the cloud got nearer, he could see the little fibers on the silk get raised, and there was a key at the end of it, and that's where the electricity, the charge collected, and then he was able to put it into a Leyden jar, or a battery. Voiceover: So really what he was doing, is he was connecting, because the clouds are getting a, they're kind of at a different electric potential up here, by kind of connecting it with his conducting silk thread that's wet, he was able kind of to get the Leyden jar to save potential. It wasn't like the lightning struck like Back to the Future. Voiceover: No, it wasn't like lightning striking him, he was drawing some of the charge down from the cloud, but that showed him that what lightning was, was a discharge from the cloud of its electric potential. Voiceover: Right, and that's significant, 'cause when he figured that out, that you could manipulate electric, that lighting was electricity, that he could kind of solve the church problem. Voiceover: The big, big problem, and you look at that kite you've drawn, what does that show you? It says, I get it, if we put something up there like that, like a lightning rod, and he knew that pointed metal objects were very good at drawing the flow of electricity, so he said, why don't we put up a lightning rod, and he described exactly how to do it. They ended up testing it in France, first, 'cause he published the lightning rod way of doing it, but later on he replicates the experiments in the United States, and it makes him the most famous person probably, other than maybe the King of France, and the King of England, the most famous person in the world because he has solved this astonishingly big problem of how do we ward off lightning from striking our building. Voiceover: Especially tall buildings like church and castle towers, and this is where he saves lives, this is a... Voiceover: Oh saves hundreds of lives, by far the most important invention of the time, and of course, we still use lightning rods, we still ground, have grounded points on top of buildings to make sure... Voiceover: It's a very simple idea, that you give kind of this pointed conductor point, that's really high up, the lightning will want to strike that, and then you construct a path for the lightning, so it can go to the ground, and not have to go through the building. Voiceover: And what he does in his house in Philadelphia, especially 'cause he's about to go to England again at the time, he puts up a lightning rod, he grounds it, but he puts a tiny little bell, so that when the electricity's coming down from the storm is approaching, and it's drawing the electrical charge from the clouds, a tiny little bell will sort of bounce back and forth, being jolted by the charges coming there, and it drove Deborah Read, his wife, absolutely to distraction, so there's a wonderful letter he writes home from England, telling her how to dismantle the bell, and it will still be safe. Voiceover: Fascinating.