  With acceptance of the Dirac's observation that the \textit{canonical
quantization entails using Cartesian coordinates, }we examine the\textit{\ }%
operator $\mathbf{e}_{r}P_{r}$ rather than $P_{r}$ itself and demonstrate that
there is a decomposition of $\mathbf{e}_{r}P_{r}$ into two self-adjoint but
non-commutative parts, in which one is the total momentum and another is the
transverse one. This study renders the operator $P_{r}$ indirectly measurable
and physically meaningful.
