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 æquinoctial 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 æquilibrio changes neither the power nor the verticity of the magnetick body. Chap. 15. The Poles, Æquator, 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' compass, are to be rubbed, that they may acquire stronger verticity. {viij} _Book 4._ Chap. 1. On Variation. Chap. 2. That the variation is caused by the inæquality of the projecting parts of the earth. Chap. 3. The variation in any one place is constant. Chap. 4. The arc of variation is not changed equally in proportion to the distance of places. Chap. 5. An island in Ocean does not change the variation, as neither do mines of loadstone. Chap. 6. The variation and direction arise from the disponent power of the earth, and from the natural magnetick tendency to rotation, not from attraction, or from coition, or from other occult cause. Chap. 7. Why the variation from that lateral cause is not greater than has hitherto been observed, having been rarely seen to reach two points of the mariners' compass, except near the pole.