“…Electromagnetic torques arise from the interaction between the magnetic field within the core and the flow of electric currents in the weakly conducting mantle that are induced both by time variations of the magnetic field and by diffusion of electric currents from the core to the mantle (Bullard et al, 1950;Dumberry and Mound, 2008;Holme, 1998aHolme, ,b, 2000Jault and Le Mouël, 1991;Love and Bloxham, 1994;Mound and Buffett, 2005;Nakada, 2006Nakada, , 2009aNakada, , 2011Roberts, 1972;Rochester, 1960Rochester, , 1962Roden, 1963;Stewart et al, 1995;Stix and Roberts, 1984;Jault, 1999, 2000). The strength of this electromagnetic torque, a mechanism first suggested by Bullard et al (1950), depends both on the conductivity of the mantle and on the strength of the magnetic field crossing the core-mantle boundary.…”