The effect of a small amount of Brownian diffusion on gravitational coagulation is numerically calculated by incorporating gravIn order to find the effect of a small amount of Brownian diffusion on gravity-induced coagulation, we need to solve the conservation equation (5): itational and interparticle forces (both attractive and repulsive), as well as hydrodynamic interactions. It is found that weak Brownian diffusion, the effect of which is nonlinearly coupled with gravity,can act to decrease the coagulation rate. ᭧ 1998 Academic Press