The First Principles of Natural Things (1845) - Page 26

...interiorly, by friction against a magnet, into either a straight line or any other regular pattern.

We show, moreover, that the declination of the magnet Magnetic declination is the angle between magnetic north and true north, which varies by location. arises from the arrangement original: "situation" of these same particles of the first and second element, or of the same element from which the vortices In Swedenborg's physics, a "vortex" is a swirling motion of subtle particles that creates a field of force, such as gravity or magnetism. around the sun and the earth are formed. We show that the magnet, along with its magnetic sphere, is directed into that same orientation in which the particles of the aforementioned element are positioned. Since these elementary particles also create a vortex around the earth, they must necessarily follow a spiral path extending from one pole of the ecliptic The ecliptic is the circular path of the Sun's apparent motion across the sky; Swedenborg suggests magnetic forces follow this celestial geometry. to the other; from this, the anomalies of magnetism arise.

See the Second Part of the Principia regarding the causes of magnetic forces:

On the attractive forces of two or more magnets, and the ratio of these forces to their distances.
On the attractive forces of two magnets when their poles are swapped original: "alternated".
On the attractive forces of two magnets when their axes are parallel, or when the equator original: "equinoctial" of one lies upon the equator of the other.
On the separating original: "disjunctive" and repulsive forces of two or more magnets, when similar or opposing original: "cognominal or inimical" poles are brought together.
On the attractive forces between the magnet and iron.
On the influence of the magnet on heated original: "ignited" iron.
On the quantity of emissions original: "exhalations" from the magnet, and how they penetrate through solid bodies, etc.
On the various ways of destroying the power of the magnet, and on the chemical experiments performed with it.
On the friction of a magnet against iron, and the force transferred from the magnet to the iron.
On the binding original: "conjunctive" force of the magnet as it acts upon several pieces of iron.
On the influence of iron and the magnet on the compass needle.
On the various ways of making iron magnetic.
On the calculations used to determine magnetic declinations.
Tables of observations regarding magnetic declination in different locations and at different times.