A Lagrangian formulation is used to discuss the nature of the force on a moving dislocation. Whether or not a Lorentz force appears depends on the definition of force adopted, but it is shown that this force can give rise to no physical effects; a definition which does not introduce it is therefore recommended. The force is given by the usual static expression ($F=\sigma b$) and is independent of the motion of the dislocation.

• Received 9 May 1962

DOI:https://doi.org/10.1103/PhysRev.128.55