That gave, yes. And the conclusions were, initially, some of the conclusions were very unexpected. Indeed, it seems that Maxwell, when he first published his paper, thought he was likely to be disproving the kinetic theory rather than proving it. Can you take that on, Steve? Why did you think so? Well,

I mean, there was some rather strange-looking conclusions like the viscosity of a gas didn't depend on its density. You mean what? That means that the viscosity is maybe how a part, how, let's say, drop a ball in the air, how it's slowed down by interacting with the air. And in fact, you might expect that to depend on the density of a gas, fewer molecules, but actually in terms of Maxwell's equations, it doesn't. And so there were some rather strange predictions, but they all mainly came true. But maybe I could just add one more prediction that also came true. His theory of velocity involved the mean-free path that Ted mentioned earlier. And meanwhile, while all this physics was going on, the chemists, of course, had been working on their own version of the atomic theory starting way back with Dalton and Avogadro. And they believed in Avogadro's number, the number of molecules in a certain volume. And measurements of diffusion of a gas, giving the mean-free path and hence the molecular diameter, allowed the first proper estimate of Avogadro's number. And suddenly, physicists and chemists together could tell you how many molecules there were in this room, for example. Yes, and I

think that was really critical.