  Space-time--time couples Kaluza's five-dimensional geometry with Weyl's
conformal space-time geometry to produce an extension that goes beyond what
either of those theories can achieve by itself. Kaluza's ``cylinder condition''
is replaced by an ``exponential expansion constraint'' that causes translations
along the secondary time dimension to induce both the electromagnetic gauge
transformations found in the Kaluza and the Weyl theories and the metrical
gauge transformations unique to the Weyl theory, related as Weyl had
postulated. A space-time--time geodesic describes a test particle whose rest
mass, space-time momentum, and electric charge q, all defined kinematically,
evolve in accord with definite dynamical laws. Its motion is governed by four
apparent forces: the Einstein gravitational force, the Lorentz electromagnetic
force, a force proportional to the electromagnetic potential, and a force
proportional to a scalar field's gradient d(ln phi). The test particles exhibit
quantum behavior: (1) they appear and disappear in full-blown motion at
definite events; (2) all that share an event E of appearance or disappearance
do so with the same charge magnitude |q| = phi(E); (3) conservation of
space-time--time momentum at such an event entails conservation of electric
charge in addition to conservation of space-time momentum, among the
participating particles; (4) at such events the d(ln phi) force infinitely
dominates the other three --- this strongly biases the appearance and
disappearance events to be concentrated deep in the discretely spaced potential
wells of ln phi, and sparse elsewhere.
