Magnetical Instructions - For the Use of Portable Instruments Adapted for Magnetic Surveys and Portable Observatories, and for the Use of a Set of Small Instruments Adapted for a Fixed Magnetical Observatory; With Forms for the Registr... #263165

The elements on which the determination of the Earth's Magnetic force is usually based, are the declination, the inclination or dip, and the intensity the declination is the angle which the magnetic axis of a freely suspended magnet, or the line of the magnetic meridian, makes with the true or astronomical meridian the inclination is the angle by which one of the extremities of a dipping needle, or magnet freely suspended by its centre of gravity, dips below the horizon; the intensity is the force exerted on a dipping needle (or magnet so suspended) to retain it in its position of equilibrium, or the power with which, when withdrawn from this position, it tends to revert to it.