In Fig. 4.6, P _{1} and P _{2} are (perfect) dipoles a distance r apart. What is the torque on P _{1} due to P _{2}? What is the torque on P _{2} due to P _{1}? [In each case, I want the torque on the dipole about its own center. If it bothers you that the answers are not equal and opposite, see Prob. 4.29.]