The Philosophical magazine; a journal of theoretical, experimental and applied physics . ry-power re-quired must depend on the resistances of the fault and conductorof the cable. The resistance of the conductor must be carefullyascertained. In the case of iron-covered cables, it will be difficult to connectthe ends of the cable to the galvanometer terminals without in-terfering with the zero-position of the needles. The needlesmay be deflected by a current set up between the copper con-ductor and the iron sheathing of the cable, or even by the tanksthemselves. When the resistance of the fault
The Philosophical magazine; a journal of theoretical, experimental and applied physics . ry-power re-quired must depend on the resistances of the fault and conductorof the cable. The resistance of the conductor must be carefullyascertained. In the case of iron-covered cables, it will be difficult to connectthe ends of the cable to the galvanometer terminals without in-terfering with the zero-position of the needles. The needlesmay be deflected by a current set up between the copper con-ductor and the iron sheathing of the cable, or even by the tanksthemselves. When the resistance of the fault is low, the deflected positionof the needle may be taken as zero, or the needle may be set tozero by the aid of other magnets. Care must be taken that theelectromotive force of this current shall be insignificant whencompared with that of the testing-battery. Supposing the x-esistances of the galvanometer and conductorto be known, and the two ends of the cable to be led into thetesting-room, the connexions will be made alternately as shownin figs. 1 and 2. Galvanometer.
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