tion and would draw it towards itself with no greater effort of its nature or trouble than a loadstone of a drachm weight embraces a drachm. But in all such experiments as this let the vigour of the magnets be equal; let there be also a just proportion in all of the shapes of the stones, and let the shape of the iron to be attracted be the same, and the goodness of the metal, and let the position of the poles of the loadstones be most exact. This is also no less true in the case of an armed loadstone than of an unarmed one. For the sake of experiment, let there be given a loadstone of eight ounces weight, which when armed lifts twelve ounces of iron; if you cut off from that loadstone a certain portion, which when it has been * reduced to the shape of the former whole one is then only of two ounces, such a loadstone armed lifts a piece of iron applied to it of three ounces, in proportion to the mass. In this experiment also the piece of iron of three ounces ought to have the same shape as the former one of twelve ounces; if that rose up into a cone, it is necessary that this also in the ratio of its mass should be given a pyramidal shape proportioned to the former.
CHAP. XXX.
The Shape and Mass of the Iron are of most
importance in coition.
bservation 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.
CHAP.
