A Simple Polarity Indicator
An ordinary compass, fitted flush in a wooden frame as shown in the sketch forms the basis for the polarity indicator described. The N, or north, and S, or south, points of the compass should run lengthwise with the frame with the former on the end farthest from the binding posts, C and D. Five turns of No. 18 gauge, or any similar wire are wound lengthwise around the frame and over the compass. The ends of the wires terminate at the two binding posts. Begin at C and wind toward the compass, binding the wire at D.
If the two ends of a wire are free, and it is desired to know whether there is any current present, and if so, its polarity, fasten one wire to the post C and the other to D. Before connecting the wires, hold the compass and frame in such a way that the needle is over the N point on the compass dial. If, after the wires are connected, the needle moves, there is a current flowing. If the needle is deflected toward the east, the negative wire is on C; if it is deflected toward the west, the positive wire is on C.
When it is desired to ascertain the polarity of a wire, which is covered by a floor, ceiling, or molding, hold the compass as explained, and either directly above or below the wire. Then turn on the current. If the instrument is above the wire, the wire extending parallel with it north and south, and the needle is deflected toward the west, the current is flowing from the north to the south end of the wire. If the wire runs east and west and the needle is deflected to the west, the current is running from west to east.
If the wire runs on a diagonal between the directions mentioned, and the needle is deflected toward the west, he current is flowing from the quadrant between N and W on the compass dial toward the quadrant between S and E. If the instrument is held over the wire and the needle is deflected toward E, the polarity is the opposite to that last indicated. Should the instrument be held below the wire, if the needle goes toward W, it is equivalent to going toward E when above the wire.—H. Sterling Parker, Brooklyn, New York.
¶If the white of an egg is used to seal an envelope which has no mucilage on the flap, it cannot be opened by steaming it.