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_.

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