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circuiting key is entirely clone away with.; the lever in the “ off ” position completely disconnecting one side of the galvanometer from the circuit, and connecting the cable under test to “ earth.”

When the connections are made to the terminals on the key, capacity tests are made by switching the lever to the left, and insulation tests by switching the lever to the right. With this key capacity tests may be taken either by measuring the discharge or by measuring the charge, by simply changing over the link shown between two of the back contact blocks.

For measuring insulation resistance the lever is switched to the " on ” position, this putting the battery directly on to the cable, the galvanometer not being in the circuit; on switching the lever still further to the right the galvanometer is put into circuit, with a shunt corresponding to the value marked opposite the particular stud on which the lever rests; and, since these shunts are arranged in decreasing values from the " on ” position, there is no danger of damaging the galvanometer with a large current due to a short circuit on the connections or cable, since the galvanometer is put into circuit with the largest shunt first.

The shunt is arranged on the Ayrton-Mather principle, and connections are made on to a small switch on the capacity side, so that the shunts may be used in taking capacities.

Davies' Long-Range Measuring Instrument. (Fig. 13.)

Permanent magnet moving coil type, with scale covering an arc of 220°. Particularly suitable as a laboratory instrument or for the purpose of calibration.

FIG. 13.

High Insulation Reversing Switch.

Particularly suitable for use in damp humid climates.

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