  Using results from conformal field theory, we compute several universal
amplitude ratios for the two-dimensional Ising model at criticality on a
symmetric torus. These include the correlation-length ratio x^\star =
\lim_{L\to\infty} \xi(L)/L and the first four magnetization moment ratios
V_{2n} = <{\cal M}^{2n}>/<{\cal M}^2>^n. As a corollary we get the first four
renormalized 2n-point coupling constants for the massless theory on a symmetric
torus, G_{2n}^*. We confirm these predictions by a high-precision Monte Carlo
simulation.
