Priestly had another idea which as far as we know no one had really looked into. What happens with a plant in that jar? How long would it take for the a plant to die? The assumption was that the plant would die; a plant’s another kind of organism. So he took this little sprig of mint out of his garden—and basically all of his nature experiments were done with things that were just around the house, a laundry sink he’d borrowed from his wife and glasses he’d get out of the kitchen. So he puts this mint plant in and isolates and sits around and it doesn’t die. It just keeps growing and growing, and he thinks, hmm, this is interesting.
How did Franklin get involved?
Once [Priestly] decided he’s got something, one of the first people he writes to is Franklin. We don’t have the letter that he writes to Franklin, but we have the letter that Franklin writes back. It’s one of these wonderful things because you have really direct evidence of this conversation that changed the way we think about the world. What Franklin does is he takes the experiment from this very local problem to the global level, in a brilliant way.
It seems from the historical record that Franklin really contributes this to Priestly’s little experiment. What Franklin says is that this sounds like it is a rational system and it’s probably one that exists all across the planet. There must be some way for the Earth to continue to heal itself, to purify the atmosphere. He says it is probably something that is happening everywhere and plants are probably cleaning up the air for us so that we can breathe clean air.
You write that Priestly’s thinking about religion had a major influence on Jefferson. How so?
Priestly did not believe in the divinity of Jesus. He didn’t believe Jesus was God’ son, and didn’t believe in the holy ghost and all that. That’s the founding precept of Unitarianism, that there is one god and there’s a wonderful voice of God’s vision on earth, but that that person is not the son of god. Priestly felt that rather than worshiping shrines and saints and resurrections that the clearest evidence of God’s work on earth was this tremendous advance—of the enlightenment.
What did Priestly see as the most important part of Christianity and how did his views have such a major effect on Jefferson’s?
He thought the essence of Christ’s message was progressive in the sense of doing unto others as you would have them do unto you. He was an early opponent of slavery and things like that. He was a great believer in tolerance. These views had a huge impact on Jefferson. Jefferson famously created the Jefferson Bible where he went through the Bible and eliminated all the parts that were basically supernatural and not Christ’s moral system. And he did that based almost entirely on Priestly’s book, An History of the Corruptions of Christianity.
Because of Priestly’s religious writings, and his political views, for example supporting the French and American revolutions, mobs destroyed Priestly’s house and would have killed him if they’d had the chance. So he emigrated to America. How was he received here?
He was greeted as a hero. He had tea with Washington a couple times, and Adams and Jefferson referred to Priestly 52 times (to Franklin only five times and to Washington only three) in the famous exchange of letters at the ends of their lives. The founding fathers’ intellectual makeup was such that it was impossible for them to imagine separating the insights and understandings of science and technology—they were also very very interested in technology—from their views of society and their politics. They understood that all those things were connected in all kinds of immensely interesting ways.