If you did Exercise 2.50, you found that the charge on each sphere is proportional to the radius r. As mentioned in that exercise, if the spheres are connected by a wire, no charge will flow in the wire. Imagine that one sphere is much smaller than the other. Then, since the electric field is proportional to 1/r², the field is much larger at the surface of the smaller sphere than the larger sphere, because the charge is proportional only to r. So why doesn't the charge get repelled from the smaller sphere and flow through the wire to the larger sphere? Hint: See Problem 3.10.
Exercises 165