Roll type Rayleigh convection with a linear temperature distribution along the bottom is experimentally investigated with silicone oil.
Results are: a) Convection due to the horizontal temperature gradient is an asymmetric single circulation. b) Rayleigh convection is deformed by the differential heating so that large direct convection cells (whose sense of rotation is same with that driven by the differential heating) and small indirect convection cells stand alternately. c) When stable and unstable regions exist side by side, a single convection due to the horizontal temperature gradient develops in the stable region, while deformed Rayleigh convections develop in the unstable region. d) As the horizontal gradient increases, the wave length of the Rayleigh convection tends to increase to converge to a certain value.