[CHAP. XVI].
If the Southern Portion of a Stone be lessened,
something is also taken away from the power
of the Northern Portion.
[CHAP. XVII].
On the Use and Excellence of Versoria: and how iron
versoria used as pointers in sun-dials, and the fine needles
of the mariners' compass, are to be rubbed, that
they may acquire stronger verticity.
