The logic of gauge theory is considered by tracing its development from general relativity to Yang-Mills theory, through Weyl's two gauge theories. A handful of elements---which for want of better terms can be called \emph{ geometrical justice}, \emph{ matter wave}, \emph{ second clock effect}, \emph{ twice too many energy levels}---are enough to produce Weyl's second theory; and from there, all that's needed to reach the Yang-Mills formalism is a \emph{ non-Abelian structure group} (say $\mathbb{ SU}\textrm{ (}N\textrm{ )}$).
Categories: physics.hist-ph