Chapter II
ends with the following explanation of the difference between electric and magnetic bodies, viz. all magnetic bodies come together by their joint forces (mutual strength); electric bodies attract the electric only, and the body attracted undergoes no modification through its own native force, but is drawn freely under impulsion in the ratio of its matter (composition). Bodies are attracted to electrics in a right line toward the centre of electricity: a loadstone approaches another loadstone on a line perpendicular to the circumference only at the poles, elsewhere obliquely and transversely, and adheres at the same angles. The electric motion is the motion of conservation of matter; the magnetic is that of arrangement and order. The matter of the earth’s globe is brought together and held together by itself electrically. The earth’s globe is directed and revolves magnetically; it both coheres, and, to the end it may be solid, it is in its interior fast joined.
Of the other interesting chapters in this Book II, attention is called more particularly to:
Chap. IV. “Of the strength of a loadstone and its form: the cause of coition.” The magnetic nature is proper to the earth and is implanted in all its real parts ... there is in the earth a magnetic strength or energy (_vigour_) of its own ... thus we have to treat of the earth, which is a magnetic body, a loadstone. An iron rod held in the hand is magnetized in the end where it is grasped and the magnetic force travels to the other extremity, not along the surface only but through the inside, through the middle.... Iron instantly receives from the loadstone verticity and natural conformity to it, being absolutely metamorphosed into a perfect magnet. As soon as it comes within the loadstone’s sphere of influence it changes instantly and has its form renewed, which before was dormant and inert, but now is quick and active.
Chaps. VI and XXVII illustrate the _Orbis Virtutis_ (Orb of Virtue, or the magnetic atmosphere surrounding both earth and loadstone alike), showing how the earth and loadstone conform magnetic movements, the centre of the magnetic forces of the earth being the earth’s centre and in the terrella the terrella’s centre. All loadstones alike, whether spherical or oblong, have the selfsame mode of turning to the poles of the world ... whatever the shape, verticity is present and there are poles.
Chap. VII. “Of the potency of the magnetic force, and of its spherical extension.” The magnetic energy is not hindered by any dense or opaque body, but goes out freely and diffuses its force every whither: in the case of the terrella, and in a spherical loadstone, it extends outside the body in a circle, but, in the case of an oblong loadstone, it extends into an area of form determined by the shape of, and is everywhere equidistant from, the stone itself.
Chap. XIII. “Of the magnetic axis and poles.”
Chap. XV. “The magnetic force imparted to iron is more apparent in an iron rod than in an iron sphere or cube, or iron in any other shape.”
Chap. XVI. “Motion is produced by the magnetic force through solid bodies interposed: of the interposition of a plate of iron.”
Chaps. XVII-XXII. Herein are detailed as many as twelve different experiments to prove the increased efficiency of armed loadstones.
Chap. XXV. “Intensifying the loadstone’s forces.” Magnetic bodies can restore soundness (when not totally lost) to magnetic bodies, and can give to some of them powers greater than they originally had; but to those that are by their nature in the highest degree perfect, it is not possible to give further strength.
Chap. XXVIII. “A loadstone does not attract to a fixed point or pole only, but to every part of a terrella, except the equinoctial line.”
Chap. XXIX. “Of differences of forces dependent on quantity or mass.” Four experiments.
Chaps. XXXVIII and XXXIX are the last, and they treat of the attractions of other bodies and of mutually repellant bodies. All electrics attract objects of every kind: they never repel or propel.
In the preceding