The principle of the Morse telegraph. 1887. 'Thus let E (fig. 484) be a fixed electromagnet; the insulated wires of which are attached to the two binding screws; a and b. Above this electromagnet is a lever; mn; movable about an axis,; t; and ending in an armature of soft iron; m; so that; whenever the electromagnet is traversed by a current; the armature is attracted; and the part of the lever on the right of the fulcrum! is lowered; then; when the current no longer passes; a spring; Rr raises the lever to an extent regulated by a screw; O.Suppose; for example; the electromagnet is at Bristol; and that there is a cell; P; at London; and two metal wires; A and B; by one of which the binding screw; b; is permanently connected with the negative pole of the battery; while the experimenter holds the other wire in his hand. So long as the experimenter does not place the wire; which he holds in his hand; in contact with the positive pole; the current does not pass.