Faraday's work inspired the development of electrical motors and generators. Until Maxwell pointed out the significance of Ampere's Law, there was no rigorous design method for magnetic devices. His interpretation strongly influenced the creation, by others, of the 'magnetic circuit' approach, which became the seminal design technique. This, utilizing the concept of reluctance, led to the design method for magnetic machines that is still widely in use today. The direct solution of the Maxwell equations (less the displacement current term) had to await the development of modern continuum methods to yield the field everywhere in, and around, the devices of interest, and this then permitted the application of the Maxwell stress tensor. This final refinement yielded forces and torques, and this resulted in the accurate prediction of electrical machine performance.