  We report the first quantitative measurements of the resonance frequencies of
a torus of fluid confined in a horizontal Hele-Shaw cell. By using the
unwetting property of a metal liquid, we are able to generate a stable torus of
fluid with an arbitrary aspect ratio. When subjected to vibrations, the torus
displays azimuthal patterns at its outer periphery. These lobes oscillate
radially, and their number n depends on the forcing frequency. We report the
instability ''tongues'' of the patterns up to n = 25. These resonance
frequencies are well explained by adapting to a fluid torus the usual drop
model of Lord Rayleigh. This approach could be applied to the modeling of
large-scale structures arisen transiently in vortex rings in various domains.
