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When it is required to obtain a continuous record of the temperatures a recording galvanometer is supplied, to which the name of “ thread recorder ” has been given. This instrument consists of a suspended coil galvanometer, the coil of which carries a boom, which is depressed by clockwork (every minute or half-minute as required) on to an inked thread.

This thread is thus forced against a calibrated chart carried on the drum below, and being inked, marks a dot on the paper. This method leaves the galvanometer boom quite free to take up its own position excepting at the moment when the boom is depressed, and thus pen-friction is avoided. The thread recorder may be used also instead of an ordinary ammeter or voltmeter when records are required.

In addition to the above methods of noting the E.M.F.S generated by a thermo-couple, and consequently the temperature of the source of heat, this E.M.F. can be determined by means of a potentiometer. This is more accurate, but is more laborious than the above methods.

Thermo-electric Potentiometer. (Fig. 16.) “ Electrician,” January 31st, 1908.

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FIG. 16.

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