[en] Experimental observations of the onset of convective motion in beds of inductively heated particles have been made. The data for the heat transfer coefficient have been obtained in water-cooled beds of 304 stainless steel particles. The particulated bed was formed in a 10.4 cm diameter glass jar which was insulated on the sides and at the bottom. The free surface of the overlying layer of water was maintained at a constant temperature by a copper plate cooled with tap water,. In the experiments, the height of the particulated bed and the height of the overlying fluid layer were varied systematically. The observations show that increasing the depth of the fluid layer over the bed tends to lower the critical internal Rayleigh number at which the onset of convection occurs