The shaft speed HAS to be a constant 3600 RPM to generate 60 hz (or 3000 RPM for 50 hz).

Incredibly brilliant observation - for ca. 1940; but most alternators now have more than one pole. "Lines of force" is also a rather arcaic concept, not much used in current teaching, design, analysis, or testing, and fundamentally limiting if one uses current easily available test equipment - and knows a little more than elementary math.

- Ever hear of Mr. Maxwell?
- Helmholtz?
- differential calculus?

John