Two spheres P and Q for equal radii have densities $\rho$ 1 and $\rho$ 2, respectively. The spheres are connected by a massless string and placed in liquids L1 and L2 of densities $\sigma$ 1 and $\sigma$ 2 and viscosities ${\eta _1}$ and ${\eta _2}$, respectively. They float in equilibrium with the sphere P in L1 and sphere Q in L2 and the string being taut (see figure) If sphere P along in L2 has terminal velocity vP and Q alone in L1 ha terminal velocity vQ, then