MULTIPLE PATTERNS IN SPIRAL AND BARRED GALAXIES

Our ability to locate resonances of spiral patterns in galaxies is sev erely limited if spirals are short lived and if many patterns co-exist in the same galaxy. Theoreticians are currently divided on the basic question of whether spiral patterns are long lived, but I argue that m ultiple, short-lived patterns are to be expected. Bars, on the other h and, seem to be truly long-lived features and a plausible case can be made that rings in barred galaxies are located at resonances. Even in barred galaxies, however, spirals appear to have a pattern speed that differs from that of the bar.