And had Eddington done any experiments? Or was he just kind of, was he just supposing he looked up at the sun and thought goodness, how did that work?

I think he was taking a bit of a punt actually just on the basis of the available evidence. Now by 1920 quite a lot of things about atoms had been discovered and it was a really fruitful time for this. So perhaps the most important thing was back in 1909 by Ernest Rutherford, very celebrated experimental physicist who showed that actually atoms weren't a big blob. They were mostly empty space with this bit in the middle where most of the matter was called a nucleus. And it's hard to overstate how much of a revelation that was. So there's another physicist called Ernest Mack after whom the Mack number is named. And he said something that like if the reality of atoms is real, then I completely renounced physics. I will hand back my scientific reputation. He was so kind of shocked by this. I agree with him. So Rutherford's work opened up this line of her inquiry. And what happened in the early 1930s is that some people in Rutherford's lab started basically just smashing these nuclei together. They worked out if they put lots of energy and they could overcome this repulsion. And so they built a smashing machine. And first of all, they discovered that when they fired a proton, that's the nucleus of a hydrogen atom at a lump of lithium, most of the time nothing happened, nothing interesting at all. But 10 in every 1 billion, a proton would strike the center of a lithium nucleus and just split it

into.