The Shape and Mass of the Iron are of most _importance in coition_. Observation has shown above that the shape and mass of the loadstone have great influence in magnetick coitions; likewise also the shape and mass of the iron bodies give back more powerful and steady forces. Oblong iron rods are both drawn more quickly to a loadstone and cleave to it with greater obstinacy than round or square pieces, for the same reasons which we have proven in the case of the loadstone. But, moreover, this is also worthy of observation, that a smaller piece of iron, to which is hung a weight of another material, so that it is altogether in weight equal to another large whole piece of iron of a right weight * (as regards the strength of the loadstone), is not lifted by the loadstone as the larger piece of iron would be. For a smaller piece of iron does not join with a loadstone so firmly, because it sends back less strength, and only that which is magnetick conceives strength; the foreign material hung on cannot acquire magnetick forces. * * * * * {99} CHAP. XXXI. On Long and Round Stones. Pieces of iron join more firmly with a long stone than with a round one, provided that the pole of the stone is at the extremity and end of its length; because, forsooth, in the case of a long stone, a magnetick is directed at the end straight towards the body in which the virtue proceeds in straighter lines and through the longer diameter. But a somewhat long stone has but little power on the side, much less indeed than a round one. It is demonstrable[180], indeed, that at A and B the coition is * stronger in a round stone than at C and D, at like distances from the pole. [Illustration] * * * * * CHAP. XXXII. Certain Problems and Magnetick Experiments about the Coition, and Separation, and regular Motion _of bodies magnetical_. Equal loadstones come together with equal incitation. * Also magnetick bodies of iron, if alike in all respects, * come together when excited with similar incitation. Furthermore, bodies of iron not excited by a * loadstone, if they are alike and not weighed down by their bulk, move towards one another with equal motion. Two loadstones, disposed on the surface of some water in {100} suitable skiffs, if they are drawn up suitably within their orbes of virtue, incite one another mutually to an embrace. So a proportionate * piece of iron in one skiff hurries with the same speed towards the loadstone as the loadstone itself in its boat strives towards the iron. From their own positions, indeed, they are so borne together, that they are joined and come to rest at length in the middle of the space. Two iron wires magnetically excited, floating in water by means of * suitable pieces of cork, strive to touch and mutually strike one another with their corresponding ends, and are conjoined.