TAPPER FORM.

IMG:8956969607833025625_520F323.JPG: Fig. 323. DOUBLE TAPPER KEY FOR SINGLE NEEDLE TELEGRAPH. C and Z are two strips of metal to which the positive and negative poles of the battery are respectively connected. E and L are two metallic springs; E is connected to earth, L is connected to the line; at rest both pre against Z. If L is depre ed so as to touch C, the current from the battery goes to the line by the key L, goes through the coils of the distant instrument and deflects the needle to one side, and then goes to the earth. If the key E is depre ed, L retaining its normal position, the direction of the current is reversed, for the other pole of the battery is connected to the earth and the reverse current going through the coils of the distant instrument deflects the galvanometer needle to the other side. In the drop-handle type an analogous form of commutator worked by a single handle produces the same effects. 521   STANDARD ELECTRICAL DICTIONARY.