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Ohmer Insulation Testing Set. FIG. 17.

The generator is compact and runs on roller bearings, and is fitted with a “free wheel clutch,” so that it cannot be suddenly stopped by stopping the handle ; carbon brushes are fitted which are easily replaceable, and the wear of the commutator is inappreciable. The generators are wound to give two standard pressures of either 500 or 1,000 volts. The ohmmeter is arranged to read to 20, 50, or 100 megohms ; the 1,000 volt set is only made in the two last ranges. A special modification is a set giving both 500 and 1,000 volts, a vibrating reed attachment being fitted to indicate which voltage the generator is producing; the higher voltage is obtained by turning the handle at a higher speed ; by this means the advantages of two generators are obtained with one. The set weighs about 62 kilos complete. In connection with this an adjustable liquid resistance is made by which the range of the instrument may be increased to 500 or 1,000 megohms.

The “ Telethermometer ” (Figs. 18 and 19).—This is an apparatus for indicating accurately the temperature in a " cold store,” or any place where access is difficult, such as tanks of liquid, &c. It consists essentially of two parts, an indicating

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