Rays of magnetick virtue spread out in every direction in an orbe; the centre of this orbe is not at the pole (as Baptista Porta reckons, Chap. 22), but in the centre of the stone and of the terrella. So also the centre of the earth is the centre of the magnetick motions of the earth; though magneticks are not borne directly toward the centre by magnetical motion, except when they are attracted by the true pole. For since the formal {96} power of the stone and of the earth does not promote anything but the unity and conformity of disjoined bodies, it comes about that everywhere at an equal distance from the centre or from the circumference, just as it seems to attract perpendicularly at one place, so at another it is able even to dispose and to turn, provided the stone is not uneven in virtue. For if at the distance C from the pole D the stone is able to allure a versorium, * at an equally long interval above the æquator at A that stone can also direct and turn the versorium. So the very centre and middle of the terrella is the centre of its virtue, and from this to the circumference of the orbe (at equal intervals on every side) its magnetick virtues are emitted. [Illustration] * * * * * CHAP. XXVIII. A Loadstone attracts magneticks not only to a fixed point or pole, but to every part of a _terrella save the æquinoctial zone_. Coitions are always more powerful when poles are near poles, since in them by the concordancy of the whole there exists a stronger force; wherefore the one embraces the other more strongly. Places declining from the poles have attractive forces, but a little weaker and languid in the ratio of their distance; so that at length on the æquinoctial circle they are utterly enervated and evanescent. Neither do even the poles attract as mathematical points; nor do magneticks come into conjunction by their own poles, only on the poles of a loadstone. But coition {97} is made on every part of the periphery, both Northern and Southern, by virtue emanating from the whole body; magneticks nevertheless incline languidly towards magneticks in the parts bordering on the æquator, but quickly in places nearer the pole. Wherefore not the poles, not the parts alone nearest to the pole allure and invite magneticks, but magneticks are disposed and turned round and combine with magneticks in proportion as the parts facing and adjoined unite their forces together, which are always of the same potency in the same parallel, unless they are distributed otherwise from causes of variation. * * * * * CHAP. XXIX. On Variety of Strength due to Quantity _or Mass_.