On the Magnet

OF CHAPTERS.

Cap. 3. The variation of every place is constant.
Cap. 4. The arc of variation is not changed equally according to the distances of places.
Cap. 5. An island in the ocean does not change the variation, nor do metals of magnets.
Cap. 6. That variation and direction are from the disposing force of the earth and the convertible magnetic nature, not from attraction or coition, or another hidden cause.
Cap. 7. Why the variation is not greater from that lateral cause than has been observed hitherto, which rarely was seen to touch two points of the nautical compass, except near the pole.
Cap. 8. Of the composition of the common nautical compass, and of the diversity of compasses of different peoples.
Cap. 9. Whether terrestrial longitude can be found through variation.
Cap. 10. Why in various places near the pole, variations are much greater than in lesser latitude.
Cap. 11. The error of Cardanus, who sought the distance of the center of the earth from the center of the world through the motion of the Herculean stone the magnet in Book 5 of his De Proportionibus.
Cap. 12. Of finding the quantity of variation: how great the arc of the Horizon is from the arctic or antarctic intersection of the meridian to the respect of the magnetic iron.
Cap. 13. Observations of variation by sailors are for the most part various and uncertain: partly from error and ignorance, and imperfections of instruments; partly because the sea is rarely so calm that shadows or lights can be held justly in the instruments.
Cap. 14. Of variation under the equinoctial line, and near it.
Cap. 15. The variation of magnetic iron in the great Ethiopian and American seas, beyond the equator.
Cap. 16. Of variation in Nova Zembla.
Cap. 17. Variation in the sea of Zur the Pacific Ocean.
Cap. 18. Of variation in the Mediterranean sea.
Cap. 19. Variation in the great Mediterranean continents.
Cap. 20. Variation in the Eastern Ocean.
Cap. 21. How the deviation of the pointer is intended and remitted due to the distances of places.

Book 5.

Cap. 1. Of declination.
Cap. 2. A diagram of the declinations of excited magnetic iron; in various positions of the sphere, and horizons of the earth, in which there is no variation of declination.
Cap. 3. An ostensive instrument, indicating by the virtue of the stone the degrees of declination, from the horizon of every latitude.
Cap. 4. Of the convenient length of the pointer upon the terrella, for declination.
Cap. 5. That declination is not from the attraction of the magnet, but from the disposing and converting virtue.
Cap. 6. Of the proportion of declination according to the ratio of latitude and of its cause.