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 aequator, 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_.

Quite similar in potency are those stones which are of the same mine, and
not corrupted by adjacent ores or veins. Nevertheless that which excels in
size shows greater powers, since it seizes greater weights and has a wider
orbe of virtue. For a loadstone weighing one ounce does not lift a large
nail as does one weighing a pound, nor does it rule so widely, nor extend
its forces; and if from a loadstone of a pound weight a portion is taken
away, something of its power will be seen to go also; for when a portion is
abstracted the virtue is lessened. But if that part is properly applied and
united to it, though it is not fastened * to nor grown into it, yet by the
application it obtains its pristine power and its vigour returns.
Sometimes, however, when a part is taken away, the virtue turns out to be
stronger on account of the * bad shape of the stone, namely, when the
vigour is scattered through inconvenient angles. In various species the
ratio is various, for one stone of a drachm weight draws more than another
of twenty pounds. Since in very many the influence is so effete that it can
hardly be perceived, those weak stones are surpassed by prepared pieces of
clay. But, it may be asked[179], if a stone of the same species and
goodness weighing a drachm would seize upon a drachm of iron, would a stone
of an ounce weight seize on an ounce, a pound on a pound, and so on? And
this is indeed true; for it both strains and remits its strength
proportionately, so that if a loadstone, one drachm of which would attract
one drachm of iron, were in equal proportion applied either to a suitably
large obelisk or to an immense pyramid of iron, it would lift it directly
in such {98} proportion and would draw it towards itself with no greater