How magnetick pieces of Iron and smaller loadstones conform themselves to a terrella & to the earth itself, and by them are disposed

Coition of those bodies which are divided, and do not naturally cohære, if they are free, occurs through another kind of motion.

A terrella sends out in an orbe its powers in proportion to its vigour and quality. But when iron or any other magnetick of convenient magnitude comes within its orbe of virtue, it is allured; but the nearer it comes to the body, the more quickly it runs up to it.

They move towards the magnet, not as *to a centre, nor towards its centre. For they only do this in the case of the poles themselves, when namely that which is being allured, and the pole of the loadstone, and its centre, are in the same straight line.

But in the intervening spaces they tend obliquely, just as is evident in the following figure, in which it is shown how the influence is extended to the adjoining magneticks within the orbe; in the case of the poles straight out.

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Oblique Magneticks.

The nearer the parts are to the æquinoctial, the more obliquely are magneticals allured; but the parts nearer the poles appeal more directly, at the poles quite straight. The principle of the turning of all loadstones, of those which are round and those which are long, is the same, but in the case of the long ones the experiment is easier.

For in whatever form they are the verticity exists, and there are poles; but on account of bad and unequal form, they are often hindered by certain evils. If the stone were long, the vertex is at the ends, not on the sides; it allures more strongly at the vertex. For the parts bring together stronger forces to the pole in right lines than oblique.

So the stone and the earth conform their magnetick motions by their nature.

Chapter 7: The Potency of the Magnetick Virtue, and on its nature capable of spreading out into an orb

From about a magnetical body the virtue magnetical is poured out on every side around in an orbe; around a terrella; in the case of other shapes of stones, more confusedly and unevenly. But yet there exists in nature no orbe or permanent or essential virtue spread through the air, but a magnet {77}only excites magneticks at a convenient distance from it. And as light comes in an instant (as the opticians teach), so much more[165] quickly is the magnetick vigour present within the limits of its strength; and because its activity is much more subtile than light, and does not consent with a non-magnetick substance, it has no intercourse with air, water, or any non-magnetick; nor does it move a magnetick with any motion by forces rushing upon it, but being present in an instant, it invites friendly bodies. And as light strikes an object, so a loadstone strikes a magnetick body and excites it. And just as light does not remain in the air above vapours and effluvia, and is not reflected from those spaces, so neither is the magnetick ray held in air or water. The appearances of things are apprehended in an instant in mirrors and in the eye by means of light; so the magnetick virtue seizes upon magneticks. Without the more intangible and shining bodies, the appearances of things are not seized or reflected; so without magnetical objects the magnetick power is not perceived, nor are the forces thus conceived sent back again to the magnetick substance. In this, however, the magnetick power excels light, in that it is not hindered by any opaque or solid substance, but proceeds freely, and extends its forces on every side. In a terrella and globe-shaped loadstone the magnetick power is extended outside the body in an orbe; in a longer one, however, not in an orbe, but it is extended in an ambit conformably to the shape of the stone. As in the somewhat long stone A, the vigour is extended to the ambient limit F C D, equidistant on every side from the stone A.

Vigour of a long stone.

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