ap. 39. On Bodies which mutually repel one another.

_Book 3._

Chap. 1. On Direction.

Chap. 2. The Directive or Versorial Virtue (which we call verticity): what
it is, how it exists in the loadstone; and in what way it is acquired when
innate.

Chap. 3. How Iron acquires Verticity through a loadstone, and how that
verticity is lost and changed.

Chap. 4. Why Iron touched by a Loadstone acquires an opposite verticity,
and why iron touched by the true Northern side of a stone turns to the
North of the earth, by the true Southern side to the South; and does not
turn to the South when rubbed by the Northern point of the stone, and when
by the Southern to the North, as all who have written on the Loadstone have
falsely supposed.

Chap. 5. On the Touching of pieces of Iron of divers shapes.

Chap. 6. What seems an Opposing Motion in Magneticks is a proper motion
toward unity.

Chap. 7. A determined Verticity and a disponent Faculty are what arrange
magneticks, not a force, attracting them or pulling them together, nor
merely a strongish coition or unition.

Chap. 8. Of Discords between pieces of Iron upon the same pole of a
Loadstone, and how they can agree and stand joined together.

Chap. 9. Figures illustrating direction and showing varieties of rotations.

Chap. 10. On Mutation of Verticity and of Magnetick Properties, or on
alteration in the power excited by a loadstone.

Chap. 11. On the Rubbing of a piece of Iron on a Loadstone in places midway
between the poles, and upon the aequinoctial of a terrella.

Chap. 12. In what way Verticity exists in any Iron that has been smelted
though not excited by a loadstone.

Chap. 13. Why no other Body, excepting a magnetick, is imbued with
verticity by being rubbed on a loadstone, and why no body is able to instil
and excite that virtue, unless it be a magnetick.

Chap. 14. The Placing of a Loadstone above or below a magnetick body
suspended in aequilibrio changes neither the power nor the verticity of the
magnetick body.

Chap. 15. The Poles, Aequator, Centre in an entire Loadstone remain and
continue steady; by diminution and separation of some part they vary and
acquire other positions.

Chap. 16. If the Southern Portion of a Stone be lessened, something is also
taken away from the power of the Northern Portion.

Chap. 17. On the Use and Excellence of Versoria: and how iron versoria used
as pointers in sun-dials, and the fine needles of the mariners' comp