Abstract
The paper mathematically establishes that the complex growth rate (p r, p i) of an arbitrary neutral or unstable oscillatory perturbation of growing amplitude, in a triply diffusive fluid layer with one of the components as heat with diffusivity, must lie inside a semicircle in the right-half of the (p r, p i)-plane whose centre is origin and radius equals (where, R 1 and R 2 are the Rayleigh numbers for the two concentration components with diffusivities 1 and 2 (with no loss of generality, > 1 > 2) and is the Prandtl number.Further, it is proved that above result is uniformly valid for quite general nature of the bounding surfaces.