I read Principia. I could follow the proofs through about 3/4ths of it. It really is tricky. I had an easier time of it as I had read (several times) Euclids e

I read Principia. I could follow the proofs through about 3/4ths of it. It really is tricky. I had an easier time of it as I had read (several times) Euclids elements. So, the geometric proofs weren’t off-putting. Nevertheless, Principia is a difficult book to follow towards the end. At the end of the day, all he’s doing is providing a geometric proof as to why an inverse squared force will (must) produce an elliptical orbit. But, damn, he takes a winding path to get there, resorting to several new concepts along the way.