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This potentiometer, constructed specially for use with thermo-couples, is designed to measure accurately small diffe-ences of potential not exceeding 30 millivolts. It enables the unknown potential difference to be accurately balanced against the E.M.F. of a standard Weston normal cell. It reads directly to 1/100 millivolt, and by estimation to 1 microvolt.

The total resistance in the circuit is arranged so as to give a fall of potential of about 1 volt per 50 ohms circuit resistance.

The key is a special double key arrangement, by which the galvanometer can be put in circuit either with the standard cell or the unknown P.D. It is thus possible, when measuring the unknown P.D., to test the accuracy of the fundamental adjustment for the standard cell without disturbing the connections. Also, by a device which locks the key when depressed on the " unknown ” circuit, it is possible to follow a rapidly changing P.D. In this way the melting point of a substance or the recalescent point of steel may be easily followed.

In order to minimise the troubles due to thermoelectric effects the only metals used in the construction of the potentiometer are copper and manganin.

Le texte affiché peut comporter un certain nombre d'erreurs. En effet, le mode texte de ce document a été généré de façon automatique par un programme de reconnaissance optique de caractères (OCR). Le taux de reconnaissance estimé pour cette page est de 99,92 %.

La langue de reconnaissance de l'OCR est l'Anglais.