  This work extends to six dimensions the idea first proposed by Klein
regarding a closed space in the context of a fifth dimension and its link to
quantum theory. The main result is a formula that expresses the value of the
characteristic length of the sixth dimension in terms of the strength of a
magnetic monopole $g$. It is shown that in the case of Dirac's monopole, the
ratio of the characteristic lengths of the fifth and sixth dimension
corresponds to twice the fine structure constant $\alpha$. Possible
consequences of the idea are discussed.

General Relativity and Quantum Cosmology