Priestley got started in science by first just trying to be something of a compiler of a history on the new science of electricity. But he was encouraged by Ben Franklin and others to carry out his own experiments, and soon became a leading 'electrician' of the day. From there, he went on to the study of gases. PETA would be a bit unhappy at the number of mice he asphyxiated, but it ultimately led to the discovery for which he's most famous: oxygen. Noting that mice snuff it after breathing up the air in a closed container, he wondered what would happen to plants. They didn't seem to give a shit. Even if you let a mouse breathe up the air until it dies, and then put a 'sprig of mint' in there, it doesn't seem to care. Priestley seemed to try all sorts of combinations almost at random, but in hindsight the crucial experiment was letting a mouse asphyxiate, then putting a mint plant in there for a few days, and then putting another mouse in there. Instead of quickly suffocating, the mouse seems to do just fine. A little more investigation, and Priestley announced the discovery of dephlogisticated air. Of course, there's no element DphlgstctdA on the periodic table, because the word oxygen is due to Lavoisier, who also has a good claim to the discovery of oxygen. Better yet, Lavoisier didn't stubbornly stick to the phlogiston theory of heat, as Priestley did.
Although I like that Johnson takes some well-calculated swings at Kuhn, I'm not sure I entirely buy his replacement idea, which is the ecosystem theory of scientific advances. Although ecosystem gives it a very eco-friendly name, I'm not sure it adds anything more to the idea that Priestley was a man of his day and age, and in constant contact with other thinkers and ideas. Johnson tries to add in an idea of 'energy flow' in the ecosystem -- that the availability of coal power helped to fuel the scientific revolution of its time. But again, I think incorporating this into the idea of an 'ecosystem' seems to be taking the analogy or metaphor too literally.
The book spends the least time on Priestley's religious dissent, which led to him becoming an early Unitarian. And as was possible in the day, this was not a codeword for sneaky atheist. Despite his rational materialism, he seems to have had a deep and abiding faith in God. Johnson credits Priestley with giving Jefferson a way to have a real faith while rejecting irrationality.
Though living in England most of his life, Priestley was a supporter of the American Revolution. And later a supporter of the French Revolution. This led to a bit of unpleasantness when his (and his friends') support for the French Revolution was seen as an attack on English monarchy. A riot ensued, and his house was burned down.
Perhaps unsurprisingly, he eventually relocated to America, where he settled in a relatively obscure spot in Pennsylvania. He couldn't keep his firebrand mouth shut, and ultimately fell afoul of the Alien & Sedition Act. Adams apparently intervened to prevent his prosecution. The book then turns more toward the discussion by letter between Jefferson and Adams which took place after Priestley's death, and when both of them were past their presidential years. Apparently Priestley is named more frequently than Washington or Franklin.
Truly a fine book about an interesting character with a lot of aspects to his life.
I was surprised when I looked at the blurb that Johnson's bio includes the fact that he is a founder of plastic.com