The controlling force is supplied partly by the suspending quartz fibre, but chiefly by the controlling magnet B, placed at the back of the instrument.

The faces of the ebonite coil boxes E are covered with a metallic shield which, together with the metal frame, completely protects the moving system from electrostatic forces. One terminal is connected to frame, which prevents large potential differences between frame and coils. The levelling screws are fitted with ebonite insulating toes.

By means of the control magnet B, the period may be varied from about 5 to 20 seconds. The damping is also adjustable, being increased by closing together the damping plates C.

Pairs of coils (E) of three resistances are supplied, viz., about 10, 100, and 1000 ohms when connected in series. Other resistances are obtained by connecting in parallel.

The instrument is very sensitive, the following being the sensitivities of some recently constructed Broca galvanometers :—

Resistance of coils in series in ohms. Period in seconds. Deflection in mm. at 1 metre Factor of | Merit.

per micro-amp. I per microvolt. per micro-coulomb.

8-8 10 350 40 220 147

8-8 17-3 1070 121 380 150

110 10 1000 9-1 630 153

110 17-3 3000 27:3 1100 159

860 10 2200 2-6 1400 148

860 17’3 6500 7’5 2400 146

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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 99,14 %.

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

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