The discovery of subatomic particles
The mix of calculation and history succeeds well in the first part of the book, dealing mostly with the properties of the electron, which could largely be described using classical physics. However, after that quantum mechanics was a requirement, and as this is beyond the intended readers of this book, there are no such calculations in the later part of the book. I would also say that the book is less useful as a motivation for studying classical physics using a more modern topic since it is now nearly a quarter of a century old, and the particle physics goes up to the beginning of the 1970's. I feel that quarks are no longer as exciting now as they were then.