If within a coil of insulated wire a piece of soft iron be placed, and i galvanic current be passed through the coil, the soft iron becomes magnetized, and continues so as long, and only as long, as the current is maintained. Now this temporary magnet exercises an inductive power on the wire, similar to that produced by a permanent magnet, and increases the force of the galvanic current in the former. If, over the coil of wire alluded to, another be placed consisting of smaller wire, this also acquires an induced state of electric action, and the intensity of the galvanic current is still further augmented. If, again, the current be interrupted, phenomena are produced of the same character as those already referred to as resulting from a similar interruption of the current in the electro-magnetic apparatus. Upon these principles instruments have been invented for the therapeutic application of electricity, which have of late been much in use, and, together with the electro-magnetic machine, have almost superseded the methods formerly employed.