have been used, with one of the coils in the transmitting circuit and the other in a local or consumption circuit the coils being differently proportioned according to the work to be done in the consumption circuit. That is to say, if the work requires a current of higher potential than that in the transmission circuit the secondary or induced coil is of greater length and resistance than the primary, while on the other hand, if a quantity current of lower potential is wanted the longer coil is made the primary.
In lieu of these devices various forms of electro-dynamic induction machines, including the combined motors and generators, have been devised. For instance, a motor is constructed in accordance with well understood principles and on the same armature are wound induced coils which constitute the generator. The motor coils are generally of fine wire and the generator coils of coarser wire so as to produce a current of greater quantity and lower potential than the line current which is of relatively high potential to avoid loss in long transmission. A similar arrangement is to wind coils corresponding to those described on a ring or similar core and by means of a commutator of suitable kind to direct the current through the inducing coils successively so as to maintain a movement of the poles of the core and of the lines of force which set up the currents in the induced coils.
Without enumerating the objections to these systems in detail, it will suffice to say that the theory or
