Knight's Mechanical Encyclopedia, T., The-od′o-lite-mag′net-om′e-ter.

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19th-Century American

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The-od′o-lite-mag′net-om′e-ter.

An instrument employed as a declinometer to measure variations in declination, and as a magnetometer in determinations of force.

It consists of a graduated horizontal circle, mounted as in the ordinary surveyor's theodolite, upon which is fixed a small wooden box. In the top of this box a vertical glass tube is fastened. The magnet is suspended in the box by means of one or two filaments of unspun silk, which pass up through the tube and are fastened at its top. The magnet consists of a perfectly turned steel tube, in one end of which there is a glass head. On this head a scale is engraved, which is so delicate that it is scarcely visible to the naked eye. The other end is closed with a lens which brings the rays of light in parallel directions to the scale. Connected with the horizontal circle of the instrument is a small telescope, mounted so that its axis shall lie in the produced axis of the box. In each end of the box is a small glass window, so that when the apparatus is properly adjusted, the light will come through the magnet to the eye of an observer, and the scale on the magnet-head will be visible.

To determine the magnet declination we have only to make the vertical wire of the telescope coincide with the axis of the magnet, and note on the horizontal circle the angle which this line makes with the direction of the true meridian, which is before determined. The variations in declination may then be determined from time to time by noting the reading of the magnet-scale.

In observations for magnetic force, Gauss's method is generally employed. The suspended magnet is made to swing horizontally in the box through a very small arc, and the time of a single oscillation is noted. The same magnet is then made to deflect another suspended magnet, from a certain fixed position and at a known distance, and the angle through which the second magnet is deflected is observed. Each of these experiments determines a value which is due to the combined effects of the magnetism of the earth and of the magnet. But these effects are, in the two cases, combined in different ways, so that, by a proper combination of the two values, we may eliminate the effect due to the magnetism of the magnet, and obtain that due to the horizontal magnetic intensity of the earth alone.

1877.

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Knight's Mechanical Encyclopedia
Knight, Ed.

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The-od′o-lite-mag′net-om′e-ter.

Knight's Mechanical Encyclopedia Knight, Ed.

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The-od′o-lite-mag′net-om′e-ter.

Knight's Mechanical Encyclopedia
Knight, Ed.