Abstract
HAVING already described my absolute sine electrometer before the Physical Society and at this year's meeting of the British Association, there is no necessity for describing here more than the prominent features of the instrument. Two plates of brass, each about one foot square, their surfaces being rendered true planes, are connected together, as a rigid body, by four ivory axes passing through both plates near their corners. On these axes are placed (between the plates) washers of mica, which serve to keep the plates asunder and parallel at a very small distance from each other. One of the plates is continuous; the other (the guard plate) has in its centre a square aperture whose side is 3 centimetres long, and in this aperture hangs a very light disk of aluminium suspended from the top of the guard plate by two Wollaston platinum wires each about 7.5 inches long. The disk is flush with the guard plate when it rests against four fine screws attached to the latter. The system of plates is movable, as a rigid body, round a horizontal axis, and its motion is produced by a micrometer screw (1-l6th of an inch pitch) working against an insulated portion of the lower edge of the continuous plate; thus the screw tilts the system out of the vertical to a measurable amount. The horizontal axis of the plates is carefully levelled with a cathetometer, and the exact distance between the plates is determined by three readings of a spherometer taken at the aperture of the guard plate (previous to the insertion of the disk) before the mica washers are inserted between the plates (the plates being in complete contact), and three readings at the same points after the insertion of the washers. The vertical distance between the centre of the axis of plates and the point of the micrometer screw is 15 inches; the weight of the disk.2568 grammes; and the head of the micrometer screw is a circle 3 inches in diameter, divided into 1000 equal parts.
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MINCHIN, G. The Determination of Electeromotive Force in Absolute Electrostatic Measure . Nature 25, 278–280 (1882). https://doi.org/10.1038/025278b0
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DOI: https://doi.org/10.1038/025278b0